Pathology

Foundations

Two numbers organize the entire lecture

Background on the cell itself: RBCs are biconcave to maximize surface area for rapid gas exchange, live 120 days, are anucleate, and run on glucose. Anemia is decreased RBC mass, most commonly assessed by hemoglobin (RBC count and hematocrit also measure mass), and it arises from either diminished production or increased destruction. Fewer RBCs → less hemoglobin → less oxygen, giving fatigue, dyspnea, lightheadedness and angina from hypoxia, plus pale skin and mucous membranes from the low hemoglobin itself.

Reticulocyte index — is the marrow trying?

• RI >3 = appropriate marrow response — the marrow is working, so suspect destruction or loss.
• RI <2 = inadequate response — a production problem, which is this entire lecture.

The reticulocyte production index (RPI) is more accurate when the patient is severely anemic or the reticulocyte percentage is very high, because it corrects for the extra maturation time of reticulocytes released prematurely into blood.

MCV — average RBC size, in fL

Microcytic · framework

Microcytic anemias are hemoglobin-synthesis failures

MCV <80 fL, characterized by decreased Hb production and therefore hypochromasia — the cells are pale as well as small.

A shortfall in any of those components gives a microcytic anemia, which is exactly why the list looks the way it does:

• Iron deficiency anemia — not enough iron (the classic)
• Anemia of chronic disease, late — iron is present but unavailable
• Sideroblastic anemias — protoporphyrin synthesis fails
• Thalassemias — globin chains fail

Microcytic · IDA

Iron deficiency anemia

The most common anemia, and iron is the most common nutritional deficiency. Beyond the typical signs of anemia, look for koilonychia (spoon nails) and pica. Plummer-Vinson syndrome is the named triad: iron deficiency anemia + esophageal webs (dysphagia) + atrophic glossitis (beefy red tongue).

Iron in vivo

Consumed as heme (meat) and non-heme (vegetable) forms; enterocytes absorb the heme form more readily. Absorbed in the duodenum and transferred into blood via ferroportin. Transferrin carries it through the blood to liver and marrow for storage, and stored intracellular iron is bound to ferritin, which also prevents free radical formation.

Causes

Chronic bleeding, malnutrition, absorption disorders, and increased demand (pregnancy, which raises TIBC).

• Breast-fed infants and toddlers — human milk is low in iron
• Menorrhagia or gastric ulcers; colon cancer or polyps
• Gastrectomy or duodenectomy — stomach acid normally keeps iron in the reduced ferrous Fe²⁺ state, which is better absorbed than oxidized ferric Fe³⁺; lose the acid or the duodenum and you lose absorption
• Hookworm infection

Stages, in order

TIBC is a measure of transferrin molecules in the blood; % saturation is the percentage of transferrin molecules carrying iron.

Labs

Microcytic hypochromic anemia · ↑ RDW · ↓ ferritin · ↑ TIBC · ↓ serum iron · ↓ % saturation · ↑ free erythrocyte protoporphyrin.

Treatment: replete iron, typically oral ferrous sulfate.

Microcytic · ACD

Anemia of chronic disease

Anemia arising in chronic inflammatory states — chronic infections, cancer, autoimmune disorders. It is the most common anemia in hospitalized patients.

Because ferroportin is the only exit door for iron, blocking it traps iron inside enterocytes and macrophages. Absorption and recycling continue, but nothing reaches the blood — so serum iron falls while stored iron piles up. Anemia starts normocytic, normochromic and becomes microcytic with time.

Labs

↑ ferritin · ↓ TIBC · ↓ serum iron · ↓/– % saturation · ↑ free erythrocyte protoporphyrin.

Treatment: treat the underlying condition; can consider exogenous EPO.

Microcytic · sideroblastic

Sideroblastic anemias

Here the defect is in the protoporphyrin half of heme, so iron arrives normally and then has nowhere to go — which makes this the microcytic anemia with an iron overload profile.

Causes

• Congenital: X-linked, mutation in ALA synthase (ALAS, the rate-limiting step)
• Alcoholism — toxic effect on mitochondria
• Lead poisoning — inhibits ALA dehydratase and ferrochelatase
• Vitamin B6 (pyridoxine) deficiency — B6 is the cofactor for ALAS. A side effect of isoniazid, and treatable with B6
• Myelodysplastic neoplasms/syndromes

Morphology

• Ringed sideroblasts — iron-laden mitochondria visible in immature erythroid precursors, in the marrow
• Basophilic stippling — in circulating red cells, from aggregates of damaged ribosomal RNA

Labs

Typically microcytic, though the alcoholism and MDS-related forms can be normocytic or macrocytic. ↑ ferritin · ↓ TIBC · ↑ serum iron · ↑ % saturation — all four together mark an iron overload state.

Macrocytic

Macrocytic anemias

MCV >100 fL. The most common cause is megaloblastic anemia from folate or B12 deficiency, both of which cause impaired DNA synthesis. Other causes: alcoholism, liver disease, some medications, myelodysplastic neoplasms, and congenital causes such as Diamond-Blackfan anemia.

Why "megaloblastic" produces the cells it does

Impaired DNA synthesis delays nuclear maturation relative to the cytoplasm. The cytoplasm keeps growing while the nucleus lags, so the cells come out too big and immature-looking:

• In erythroid precursors → megaloblastic anemia
• In granulocytic precursors → hypersegmented neutrophils

Folate deficiency

Causes: decreased dietary intake (green vegetables, some fruit) — and critically, body stores are minimal, so deficiency develops quickly, in weeks to months. Alcohol use disorder contributes through decreased dietary variety. Also increased demand (pregnancy, or high cell turnover as in cancer or hemolytic anemias), and folate-antagonist medications.

Labs: hypersegmented neutrophils · glossitis · ↓ serum folate · ↑ homocysteine, raising thrombosis risk · normal methylmalonic acid.

B12 deficiency

Dietary deficiency is less common than folate deficiency because hepatic stores are large — so it takes years, and vegans are the dietary exception. The most common cause is pernicious anemia: intrinsic factor, made by gastric parietal cells, is required for B12 absorption in the small bowel, and PA is autoimmune destruction of parietal cells → intrinsic factor deficiency. Other causes: pancreatic insufficiency, terminal ileum damage or loss (Crohn disease), and Diphyllobothrium latum, the fish tapeworm.

Findings: hypersegmented neutrophils · glossitis · ↑ homocysteine · ↑ methylmalonic acid · neurologic symptoms, because B12 is required for fatty acid and myelin metabolism — dorsal column and lateral corticospinal tract degeneration, giving decreased proprioception and vibration sense and spastic paresis respectively.

Normocytic

Normocytic anemias of diminished production

Normocytic anemias are classically split into hemolytic and non-hemolytic. Acute blood loss is a common normocytic cause, and early IDA and early ACD live here too before they turn microcytic. The production failures:

• Renal failure → decreased EPO production
• Aplastic anemia — see below
• Parvovirus B19 — infects erythroid precursors and inhibits erythropoiesis. Especially important in patients with underlying marrow stress, such as sickle cell anemia or post-HSCT patients, where losing production for even a short time causes an abrupt crash
• Myelophthisic processes — replacement of the marrow space by something else, usually metastatic cancer. Often pancytopenia, and the peripheral smear can show marrow elements not normally in blood: nucleated red blood cells and neutrophil precursors

Aplastic anemia

Damage to stem cells by medications, infections, or autoimmune/abnormal T-cell activity; some cases idiopathic. The marrow space is void of hematopoietic elements — replaced by fat — producing pancytopenia. Treatment: discontinue causative medications, supportive care, and HSCT in some cases.

Key points

The three tables to have memorized

Iron studies

Read it as two questions. Ferritin splits IDA (low stores) from everything else (adequate or high stores). Then serum iron and % saturation split ACD (iron trapped, so low) from sideroblastic (iron unusable, so it accumulates — high).

Folate versus B12

The MCV map

Grey entries are listed for completeness but belong to another lecture.

Highest yield

Six things to carry out of this lecture

1. RI <2 means the marrow is the problem; RI >3 means destruction or loss. That single number decides which half of anemia you are in.
2. Ferritin separates IDA from ACD. Both have low serum iron; only IDA has low ferritin and high TIBC.
3. Sideroblastic anemia is the microcytic anemia with iron overload — high ferritin, high serum iron, high % saturation — because the block is in protoporphyrin, not iron.
4. Lead inhibits ALA dehydratase and ferrochelatase; B6 is the cofactor for ALA synthase (so isoniazid can cause it, and B6 treats it). Look for basophilic stippling on smear and ringed sideroblasts in marrow.
5. MMA and neurologic findings are the only things separating B12 from folate. Both raise homocysteine; only B12 raises MMA and hits the dorsal columns and lateral corticospinal tracts.
6. Pancytopenia: empty marrow is aplastic, crowded marrow is myelophthisic — and nucleated RBCs with granulocyte precursors on the smear point to the latter.

Form follows function

What the normal red cell has to do

The core job is to enclose and transport hemoglobin — delivering O₂ to tissues and carrying CO₂ to the lungs. Enclosure matters on its own, because free hemoglobin is relatively toxic, particularly to the kidneys. Secondary roles: maintaining extracellular pH and electrolyte balance, delivering toxic compounds to liver and kidney, transporting hormones, and participating in immune responses.

The cell is deliberately simple — no nucleus, no mitochondria, no lysosomes, little enzyme activity. Energy comes from breaking glucose down to lactate or pyruvate through the glycolytic (Embden-Meyerhof) pathway, and that ATP is what maintains membrane integrity. ATP-depleted red cells are more susceptible to hemolysis.

Four design requirements

• Volume — enclose the maximum amount of oxygen-binding hemoglobin
• Shape — the biconcave disc is a compromise between storage volume and surface area for gas exchange
• Deformability — to traverse small tortuous routes and heart valves, then recover shape
• Durability — to survive 120 days

Where red cells come from, and the transfusion aside

Erythropoiesis is driven by EPO, moving through yolk sac (aorta-gonad-mesonephros) → liver and spleen → bone marrow. Under stress, extramedullary hematopoiesis can restart in spleen, liver, and lymph nodes. Transfused units are stored in glucose solutions, refrigerated, for up to 42 days — and undergo some hemolysis with storage as ATP is depleted, which is the same ATP-membrane link again.

Hemoglobin, briefly

2 pairs of globins (2 alpha, 2 beta in adults) plus 4 heme groups, each one atom of ferrous (2+) iron held by a porphyrin ring. Oxyhemoglobin is one ferrous iron plus one O₂. Two terms to keep separate: a hemoglobinopathy is a mutation producing an abnormal globin (sickle cell), while a thalassemia is a mutation producing decreased synthesis of a normal globin.

Classifying hemolysis

Hemolysis and its three axes

Definition: destruction of red cells resulting in release of hemoglobin. Note what is not in that definition — anemia. Hemolysis may or may not cause anemia: if increased marrow production keeps up with the loss, it is compensated.

• Rapid (acute) versus slow (chronic) — chronic hemolysis is easier to tolerate, because the marrow has time to compensate
• Hereditary (intrinsic defects) versus acquired (antibodies)
• Intravascular versus extravascular

Intravascular versus extravascular

Immune versus non-immune

The mnemonic split worth holding: allo = an antibody against a foreign antigen; auto = an antibody against your own antigens.

Laboratory detection

Proving hemolysis, then localizing it

Present in any hemolysis

• Decreased hemoglobin / hematocrit
• Increased reticulocyte count, with polychromasia on the smear — the marrow responding appropriately
• Unconjugated (indirect) hyperbilirubinemia — heme is being catabolized faster than the liver conjugates it to glucuronide
• Increased LDH

Added when hemolysis is intravascular

• Decreased plasma haptoglobin — it binds free hemoglobin released from RBCs, and is consumed doing so
• Increased free hemoglobin — hemoglobinemia and hemoglobinuria

The marrow side of the picture: erythroid hyperplasia, with increased erythroid precursors stimulated by EPO. Normoblasts are nucleated RBCs.

Infections that hemolyze red cells directly

• Babesia species (e.g. B. microti) — dangerous in asplenic patients
• Plasmodium species — especially falciparum malaria
• Clostridium welchii — produces a hemolysin

Membrane defects

Hereditary spherocytosis

Red cells are fragile and less deformable, get trapped in the spleen, and survive only 10–20 days instead of 120. It is the common inherited anemia in northern Europeans (1 in 5,000), usually autosomal dominant (75%), with heterogeneous molecular defects.

Molecular defects

• Many defects are private — confined to a single family
• Reading frame shifts and introduction of stop codons are the most common mutation types
• Defects in ankyrin, spectrin, and band 4.2; ankyrin is most common
• Protein electrophoresis shows reduced spectrin and reduced ankyrin

The CBC, and why the indices look the way they do

From her worked example: MCV 82.6 (normal), MCHC 36.5 high, RDW 16.5 high.

• MCV: low to normal range — not frankly microcytic
• MCHC increased from relative cell dehydration — the cell loses K⁺ and water, so the same amount of hemoglobin sits in a smaller volume

Diagnosis and treatment

• Spherocytes on smear — they lack central pallor, and are seen in HS and WAHA, so the finding alone does not establish a hereditary cause
• Osmotic fragility test: incubate RBCs in NaCl solutions of decreasing concentration. Spherocytes are more sensitive to osmotic lysis and lyse sooner than normal RBCs — because a sphere has no spare membrane to expand into as water enters
• Splenectomy is often helpful, increasing the lifespan of the abnormal RBCs. Afterward, expect Howell-Jolly bodies (remnants of DNA) on the smear, since no spleen remains to pit them out

Membrane defects, continued

Hereditary elliptocytosis and pyropoikilocytosis

• Hereditary elliptocytosis — most commonly mutations in α-spectrin genes (SPTA1, SPTB), autosomal dominant, common in equatorial Africa because it confers resistance to malaria. Critically, the majority of patients are NOT anemic — elliptocytes are an incidental smear finding, and treatment is not necessary, since HE is uncommonly associated with hemolysis.
• Hereditary pyropoikilocytosis — the severe form of HE, autosomal recessive, and it does cause hemolysis and anemia.

Enzyme defects

G6PD deficiency

An enzyme deficiency that renders the red cell vulnerable to oxidative injury. X-linked recessive, so clinically it appears in males. The abnormal G6PD protein misfolds and is degraded, which is why the deficiency worsens as cells age. Clinically relevant variants: G6PD A− in the African American population and G6PD Mediterranean in the Middle East. Like elliptocytosis, it may protect against Plasmodium falciparum.

Removal of H₂O₂ requires reduced glutathione and glutathione peroxidase, and the hexose monophosphate shunt is the red cell's only source of NADPH to regenerate that glutathione — hence a single enzyme gap collapses the whole antioxidant defense.

Triggers — hemolysis is intermittent and acute, not chronic

• Drugs: antimalarials (primaquine, chloroquine), sulfonamides, nitrofurantoins
• Foods: fava beans — “favism”
• Viral and bacterial infections — free radicals generated by WBCs

Smear after oxidant exposure

• Heinz bodies — precipitates of denatured globin, requiring supravital staining to see
• Bite cells — splenic macrophages pick out these inclusions, taking a bite of membrane with them

Treatment is preventive: prevent exposure to oxidants. There is nothing to replace.

Hemoglobinopathy

Sickle cell disease

A hereditary hemoglobinopathy from production of an abnormal hemoglobin, and it is common — 8% of African Americans carry the sickle cell mutation.

• Sickle cell DISEASE = homozygous; sickle cell TRAIT = heterozygous
• Other β-globin chain disorders include HbC and HbE
• HbS = α₂β^S₂ = α₂β₂^Glu→Val. The change in protein charge alters electrophoretic mobility, which is what makes hemoglobin electrophoresis diagnostic — SS = disease, AS = trait, AA = normal

Pathophysiology — a self-amplifying cycle

Diagnosis

• Clinical presentation and family history
• Blood smear: DISEASE shows sickle cells; TRAIT shows normal-appearing red cells. Also polychromatic RBCs, target cells, anisocytosis (variation in size), poikilocytosis (variation in shape), and Howell-Jolly bodies with irreversibly sickled cells
• Sickling test — mix blood with an O₂-consuming reagent to promote sickling
• Hemoglobin electrophoresis or HPLC; DNA testing for prenatal diagnosis; newborn screening in all states

The spleen, in two stages

• Splenic sequestration crisis — a potentially life-threatening complication: sudden enlargement of the spleen from trapping of RBCs, with a rapid drop in Hb/Hct, hypovolemia and circulatory collapse. The spleen is congested and sinuses dilated with RBCs
• Autoinfarction / autosplenectomy — the spleen becomes small, shrunken, fibrotic, non-functional, leaving the patient susceptible to encapsulated organisms: pneumococci and Haemophilus influenzae

Cerebral infarction is monitored by transcranial Doppler measurement of cerebral blood flow, with a treatment goal of reducing HbS below 30% by transfusion.

Treatment — every goal reduces sickling

HbF works because it contains no β chains at all, so it cannot participate in HbS polymer — it dilutes the polymerizing species rather than blocking it.

Shared complications

What chronic hemolysis costs, regardless of cause

These apply across hemolytic diseases, HS and SCD included:

• Marrow expansion — to keep up with RBC demand
• Iron overload — especially in chronically transfused patients; oral iron chelators are used in sickle cell disease and severe thalassemia
• Gallstones — bilirubin (pigment) stones, from the chronic unconjugated bilirubin load
• Aplastic crisis — from viral infection, specifically Parvovirus B19 (fifth disease), causing a rapid and life-threatening drop in Hb/Hct. Marrow shows giant pronormoblasts and pure red cell aplasia

Thalassemia · framework

Thalassemia syndromes

Heterogeneous genetic disorders resulting in decreased synthesis of adult hemoglobin (HbA, α₂β₂) — either the α chains (α-thal) or the β chains (β-thal). Two consequences follow, and both matter:

• Hypochromia from reduced HbA — there simply isn't enough hemoglobin
• Relative excess of unpaired globin chains can harm RBCs — and this is the arm that actually drives the disease severity

Gene dosage explains why the two behave differently: a pair of α-globin genes on chromosome 16 gives 4 genes total, while a single β-globin gene on chromosome 11 gives 2 genes total.

Laboratory testing — alpha and beta alike

• RBC count increased — “lots of small cells”
• MCV decreased — think thalassemia if MCV <67 fL
• MCH and MCHC decreased
• Normal RDW
• Smear: hypochromic microcytic RBCs and target cells
• Electrophoresis: increased HbA2 in β-thal trait and β-thal intermedia, but NOT in α-thal

Thalassemia · beta

β-thalassemias

Molecular basis: mutations — usually point mutations, in contrast to the deletions of α-thal — that decrease β-globin synthesis.

Clinical severity is heterogeneous, and it tracks the amount of β chain made: cells are hypochromic and microcytic with reduced O₂ carrying capacity, and free α chains precipitate, causing RBC membrane damage and extravascular hemolysis.

Pathogenesis of β-thalassemia major (Cooley's anemia)

Both arms converge on anemia, which then branches again:

• Anemia → tissue hypoxia → ↑ erythropoietin → marrow expansion → skeletal deformities — classically a skull radiograph with new bone formation on the outer table producing perpendicular radiations, the “crewcut” appearance
• Ineffective erythropoiesis → increased dietary iron absorption → iron deposits in heart, liver, pancreas → systemic iron overload (secondary hemochromatosis), demonstrated on a liver Prussian blue iron stain. Iron chelation therapy minimizes it
• Blood transfusions reduce the anemia and therefore the marrow drive — but add their own iron burden

Clinical spectrum

Thalassemia · alpha

α-thalassemias

Reduced or absent α-globin chains, most commonly due to gene deletions — the key contrast with β-thal's point mutations. Because there are four α genes, severity is graded by how many are affected.

Hemoglobin electrophoresis summary

Note the one apparent oddity: HbA2 is trace in β-thal major but elevated in minor. HbA2 needs α chains too, and in major the massive HbF production dominates the percentages.

Acquired · clonal

Paroxysmal nocturnal hemoglobinuria

A rare acquired hematopoietic stem cell disease — a clonal disorder from somatic mutations affecting the RBC membrane. The specific defect is in the phosphatidylinositol glycan class A (PIG-A) gene, which is required to form the red cell anchor. The result: cells are more sensitive to complement-mediated lysis.

The two that matter functionally: CD55 (decay accelerating factor) and CD59 (membrane inhibitor of reactive lysis, which inhibits C3 convertase). Both are complement brakes, so losing them leaves the cell defenseless against ongoing low-level complement activation.

Clinical triad

• Chronic hemolytic anemia
• Thrombosis — the most common cause of mortality
• Pancytopenia — bone marrow failure

Diagnosis

• Flow cytometry is the modern test: both RBCs and granulocytes normally express GPI-anchored proteins, and PNH cells show abnormal or absent CD55 and CD59. Alternatively, FLAER (fluorescent aerolysin), which binds the glycan portion of the GPI anchor itself rather than using antibodies
• Historical tests — both work by making complement attack easier, and both are less specific than flow: the acidified serum (Ham) test, 1939, where acidified serum activates the alternative complement pathway (can be positive in congenital dyserythropoietic anemia), and the sucrose hemolysis test, 1970, where 10% sucrose provides low ionic strength promoting complement binding (can be positive in megaloblastic anemia and AIHA)

Marrow shows erythroid hyperplasia with numerous erythroid precursors. Treatment: marrow transplant, or anti-complement (C5) antibody — eculizumab — to reduce hemolysis. Median survival 10 years.

Acquired · immune

Immune hemolytic anemias

The unifying mechanism: red cells coated with antibody and/or complement are removed from the circulation, in the spleen.

The Direct Antiglobulin Test (DAT / Coombs)

Principle: detect antibody (IgG) and/or complement (C3) on the RBC surface by adding anti-human antibody and looking for agglutination. Its job is to distinguish immune from non-immune anemias — anemia plus a positive DAT points to an immune hemolytic anemia.

Warm autoimmune hemolytic anemia (WAHA)

Defined as hemolytic anemia plus an RBC autoantibody, usually idiopathic.

• Positive Coombs test
• Spherocytes in peripheral blood — her slide calls them “microspherocytes”
• The autoantibodies react with a wide range of self-antigens, so they destroy both the patient's own cells and any cells that are transfused — which is what makes transfusion support difficult
• Treatment: corticosteroids (prednisone), rituximab (anti-CD20 B cell antibody), splenectomy

Spherocytes form here for the same mechanical reason as in HS: splenic macrophages remove part of the antibody-coated membrane, and the cell rounds up. Same shape, different cause — and the DAT is what separates them.

Cold agglutinin syndrome (CAS)

• May cause a chronic autoimmune hemolytic anemia
• Thermal amplitude of the antibody determines severity — symptoms appear in fingers, toes, and cold-exposed areas, where blood is coolest
• Usually IgM, often directed against I or i antigens. The DAT detects complement on the RBCs — not IgG, because IgM elutes as blood rewarms while the complement it deposited stays behind
• Infection-associated: Mycoplasma pneumoniae, infectious mononucleosis (EBV), CMV, influenza, HIV — this form is usually self-limited
• Older adults with monoclonal gammopathies — plasma cell myeloma, lymphomas

Paroxysmal cold hemoglobinuria (PCH)

• Rare autoimmune syndrome causing massive intravascular hemolysis on cold exposure
• IgG autoantibody against the P antigen — historically associated with syphilis, and now typically following viral infection in children
• Biphasic hemolysin — the Donath-Landsteiner antibody: antibody and early complement components bind at low temperature, then terminal complement components form on warming and the cells lyse intravascularly
• Donath-Landsteiner test: patient serum plus normal (P-positive) RBCs and fresh serum as a complement source; antibody binds cold, complement lyses on warming — giving red serum in the tube (hemolysis) and cola-colored urine (hemoglobinuria)
• Treatment: self-limited; avoid cold; corticosteroids are not helpful — a deliberate contrast with WAHA

Drug-related hemolytic anemia — three mechanisms

Treatment includes identifying and stopping the offending drug — and note her emphasis that drugs can cause severe intravascular hemolysis. The distinction that matters: in the hapten and ternary-complex mechanisms the antibody needs the drug present, so hemolysis stops when the drug is withdrawn; in the autoantibody mechanism a true self-directed antibody has been created, which can persist.

Acquired · mechanical

Microangiopathic and mechanical hemolysis

Microangiopathic hemolytic anemia (MAHA)

Red cells are damaged on contact with dense fibrin strands, producing schistocytes — red cell fragments. Causes:

• Disseminated intravascular coagulation (DIC)
• Thrombotic thrombocytopenic purpura (TTP)
• Hemolytic uremic syndrome (HUS)

Mechanical hemolysis (RBC trauma)

• Artificial heart valves — tilting valve, ball-and-cage valve
• March hematuria — hematuria after repetitive impact on the body, classically the feet

Highest yield

Eight things to carry out of the hemolysis lectures

1. Hemolysis is proven by ↑retic, ↑indirect bilirubin and ↑LDH; it is localized by haptoglobin. Low haptoglobin plus hemoglobinuria means intravascular.
2. HS: ↑MCHC from cell dehydration, ↑RDW, MCV low-to-normal. Spherocytes lack central pallor and appear in both HS and WAHA — the DAT separates them.
3. G6PD is episodic and X-linked. ↓NADPH → ↓reduced glutathione → Heinz bodies → bite cells. Triggers: primaquine, sulfonamides, fava beans, infection. Treatment is avoidance.
4. Sickle cell is a point mutation at the 6th codon of β-globin, glutamate → valine. Deoxygenation polymerizes HbS; dehydration raises MCHC and makes it worse. Goals: ↑HbF (hydroxyurea), ↓HbS to <30%, avoid dehydration and acidosis.
5. Thalassemia versus IDA: normal RDW and an increased RBC count mean thalassemia, along with MCV <67. HbA2 is raised in β-thal trait but not in α-thal.
6. Chain terminator → β⁰; splicing → β⁺. Free α chains drive ineffective erythropoiesis, which drives both the marrow expansion (crewcut skull) and the increased iron absorption behind secondary hemochromatosis.
7. α-thal is graded by gene count: 3 genes deleted = HbH (β₄), 4 genes = Hb Bart (γ₄, high O₂ affinity) and hydrops fetalis.
8. PNH: PIGA mutation → no GPI anchor → no CD55/CD59 → complement lysis. Triad of hemolysis, thrombosis (leading cause of death), and pancytopenia. Diagnose by flow cytometry; treat with eculizumab.

Objective 1 · vessel wall

Vessel wall abnormalities associated with bleeding

These are the “non-thrombocytopenic purpuras” — the vessel itself is leaky or fragile, so the patient bleeds while every screening test comes back normal.

Bleeding is variable and usually mild. Causes fall into recognizable buckets:

• Infections — meningococcemia, Rickettsia
• Drug reactions — vasculitis
• Collagen disorders — scurvy, Ehlers-Danlos
• Henoch-Schönlein purpura — immune complexes
• Hereditary hemorrhagic telangiectasia
• Amyloid infiltration of blood vessels

Objective 2 · platelet basics

What platelets are, and what happens as the count falls

Platelets are small cell fragments derived from megakaryocytes, which expand and differentiate over several days in response to thrombopoietin (TPO). Their two jobs:

• Provide the surface on which coagulation factors assemble — this is why platelets and the cascade are not really separable systems
• Prevent bleeding

Platelet count and clinical consequence

Normal count is 150–450 K/µL.

Objective 2 · non-immune causes

Splenic sequestration and dilutional thrombocytopenia

Splenic sequestration (splenomegaly)

Very common. The spleen enlarges from increased cells/tissue or vascular engorgement, and pools platelets out of the circulation. Associated with:

• Infiltration by leukemia or lymphoma
• Chronic liver disease
• Congestive heart failure

Dilutional thrombocytopenia

Trauma and complicated surgery. Platelets are simply diluted by the saline, red cells, and plasma being infused. Treatment is to transfuse platelets if the count is low enough to affect hemostasis.

Objective 3 · ITP

Immune thrombocytopenic purpura — adult chronic

An autoimmune disorder manifesting as immune-mediated thrombocytopenia. Autoantibodies (IgG) recognize one or more platelet surface glycoproteins — GPIIb-IIIa, GPIb-IX, others — and are detectable in 50–80% of patients.

She points at the analogy directly: this is the same situation as warm autoimmune hemolytic anemia (WAHA), just with platelets as the target instead of red cells.

Clinical features

• Most common cause of isolated thrombocytopenia in an otherwise healthy patient
• Any age or sex, but typically young women under 40
• Splenomegaly and intracerebral bleeds are NOT common
• Signs track the count — petechiae (pinpoint hemorrhages) and ecchymoses (bruises)

Laboratory features

ITP is a diagnosis of exclusion.

• CBC and smear: isolated thrombocytopenia with large platelets
• PT and aPTT are normal — clotting factor activity is intact
• No sensitive and specific test exists. Antiplatelet-antibody assays exist but do not make the diagnosis
• Check for HIV and hepatitis C — both cause thrombocytopenia
• Marrow, when examined, shows increased megakaryocytes, and mainly serves to exclude infiltration, leukemia, lymphoma, and MDS

Objective 3 · treatment

Treating chronic ITP in adults

Options scale with severity, and they sort cleanly by mechanism:

Acute immune thrombocytopenia in children

Clinically a different disease from the adult chronic form:

• Abrupt onset, usually following a viral illness
• Usually does NOT require steroids — observation
• Spontaneous and permanent remission, in contrast with adults, who often have chronic disease with relapses

Objective 4 · HIT

Heparin-induced thrombocytopenia

A life-threatening complication of heparin exposure, and common — 1% to 5% of exposed patients. Caused by an antibody against a complex of heparin and platelet factor 4 (PF4).

Pathophysiology — her four-step sequence

Type I versus Type II HIT

The “4 Ts” score

A clinical pretest probability score. Each of four features earns 2, 1, or 0 points:

Laboratory testing — two categories

• Immunoassays detect the antibody — they use antibodies to find the anti-heparin-PF4 antibodies in the patient's blood
• Functional tests detect platelet activation — the serotonin release assay is the classic

Treatment

Objective 4 · other drugs

Other drug-induced thrombocytopenias

• Immune mechanism — antibodies react with platelet membrane glycoproteins only when the drug is present, leading to platelet removal. Quinine, quinidine, sulfonamide antibiotics.
• Non-immune mechanism — marrow failure from a direct toxic effect on the bone marrow. Many drugs; the most common are chemotherapeutic agents.

Objective 5 · HIV and pregnancy

HIV-associated and pregnancy-associated thrombocytopenia

HIV

Common in HIV disease, and multifactorial:

• Decreased production — HIV infects megakaryocytes directly
• HIV-associated ITP — increased destruction through immune-mediated thrombocytopenia, with GPIIb-IIIa autoantibodies
• Responds to antiretroviral therapy — treat the virus and the count often recovers

Pregnancy

• Gestational thrombocytopenia — incidental, mild, no specific cause, resolves after delivery
• Other causes: severe preeclampsia / HELLP, DIC, thrombotic microangiopathies
• ITP in pregnancy — roughly a 10-fold greater risk than the general population. Occurs in any trimester, severity varies, and counts change over the pregnancy. Transplacental passage of maternal autoantibody can cause fetal/neonatal thrombocytopenia in ~25%. Most pregnancies are uneventful.

Objective 5 · NAIT

Neonatal alloimmune thrombocytopenia (NAT)

Caused by platelet alloantibodies the mother develops against foreign fetal platelet antigens — the HPA-1a antibody is the classic.

• Detected in the lab by ELISA
• The mother has a normal platelet count — the antibody is against an antigen she does not have
• The FIRST child is often affected — contrast Rh disease of the newborn, where it is the second pregnancy
• May present as newborn bleeding or intracranial bleed
• Treatment: IVIG ± corticosteroids, and platelet transfusion
• Subsequent pregnancies are high-risk

Objective 6 · TTP

Thrombotic thrombocytopenic purpura

A thrombotic microangiopathy — excessive platelet activation forming thrombi in small blood vessels. TTP is a medical EMERGENCY, and the defining paradox is that patients CLOT despite being thrombocytopenic.

Pathogenesis

• ADAMTS13 is the metalloprotease that cleaves vWF. Without its activity, sticky ultra-large vWF multimers persist
• Acquired TTP — an IgG autoantibody against ADAMTS13. This is the usual form
• Rare inherited patients exist with a mutation that inactivates ADAMTS13

Laboratory findings

• Thrombocytopenia — counts are variable
• MAHA — anemia with schistocytes, reticulocytosis ± nucleated RBCs, increased LDH, unconjugated hyperbilirubinemia
• Renal dysfunction — usually only a mild creatinine rise
• PT and aPTT are usually NORMAL unless DIC develops
• ADAMTS13 activity assay

Schistocytes are RBC fragments formed when red cells come into contact with dense fibrin meshworks.

Treatment

• Corticosteroids and rituximab (anti-CD20) — decrease autoantibody production
• Caplacizumab — an anti-vWF immunoglobulin
• Splenectomy — increases platelet survival
• Platelet transfusion may be contraindicated

Drug-induced thrombotic microangiopathy is immune-mediated like TTP — quinine, ticlopidine, clopidogrel.

Objective 6 · HUS

Hemolytic uremic syndrome

“Typical” HUS

• MAHA and thrombocytopenia — same microangiopathic picture as TTP
• Prominent acute renal failure — this is the discriminator
• Neurologic symptoms less common than in TTP
• More frequent in children, who often recover
• NORMAL levels of ADAMTS13
• Most often from food contaminated with enterohemorrhagic E. coli producing Shiga-like toxins that disrupt endothelium → platelet activation
• NOT treated by plasma exchange — no specific therapy

“Atypical” HUS (aHUS)

• Non-infective cause of HUS
• Inherited (mutations in complement component genes) or sporadic
• Chronic and recurring, with >50% developing end-stage renal failure; early mortality 10–25%
• Caused by excessive complement activation
• Responds to complement inhibitors — eculizumab

Highest yield

Six things to carry out of this lecture

1. Thrombocytopenia is either decreased production or decreased survival, and decreased survival happens by immune and non-immune mechanisms. Every disease in this lecture slots into that grid.
2. Normal platelet count + normal PT/aPTT + purpura = vessel wall disease. Nothing in the routine panel tests the vessel.
3. ITP is a diagnosis of exclusion — isolated thrombocytopenia, large platelets, increased marrow megakaryocytes, and no prophylactic platelet transfusion even at zero platelets.
4. HIT clots. Antibody against heparin-PF4, onset days 5–10, platelets are activated before they are destroyed. Stopping heparin is not enough — add a direct thrombin inhibitor, and avoid platelet transfusion.
5. NAIT: first pregnancy, normal maternal platelet count. Rh disease is the second pregnancy. That contrast is the exam question.
6. TTP has normal PT and aPTT; DIC does not. TTP is ADAMTS13 deficiency treated by plasma exchange; typical HUS has normal ADAMTS13, prominent renal failure, and is not treated by exchange.

Approach

The hemostatic history, then the lab

She opens with the point that history is an important part of hemostatic evaluation, and the questions are targeted:

• Personal or family history of bleeding?
• Spontaneous bleeding, or bleeding only under hemostatic challenge — surgery, dental work, childbirth?
• Medications, vitamins, health foods?
• Type of bleed?

Laboratory tests of hemostasis

• Routine screening — platelet count, PT, aPTT, plus fibrinogen, D-dimer, thrombin time
• Specialized — bleeding time, platelet function tests, vWF testing, factor assays (F8, F9, F11)

Objective 1 · acquired

Acquired platelet function defects — the platelets don't work

Drugs and vitamins — very common:

• Cyclooxygenase inhibitors (aspirin and other NSAIDs) — inhibit thromboxane A2 production, and TxA2 stimulates platelets
• P2Y12 receptor inhibitors (clopidogrel, ticlopidine) — the P2Y12 receptor binds ADP, which is crucial for platelet activation and aggregation

Other conditions affecting platelet function:

• Uremia — multiple effects on platelet function
• Cardiac surgery — platelet activation and destruction in the bypass circuit

Tests of platelet function

• Bleeding time — standard incision, blot until bleeding stops. Difficult to perform, not reproducible, and NOT DONE ANYMORE
• Automated platelet function analyzer — platelets exposed to agonists (collagen, epinephrine, ADP). Good at detecting antiplatelet medications, vWD, and inherited function disorders

Platelet agonists are substances that activate platelets: thrombin, TxA2, ADP, collagen, epinephrine, arachidonic acid, ristocetin. Historically tested by optical platelet aggregometry; today rapid assays can determine whether a patient is on an antiplatelet drug and whether it is working.

Objective 1 · hereditary

Hereditary platelet function defects

Two receptors, two diseases, and the receptor's job tells you which step fails:

Deficiency of GPIIb-IIIa gives Glanzmann thrombasthenia; deficiency of GP1b gives Bernard-Soulier syndrome; deficiency of vWF itself gives von Willebrand disease — three defects along one pathway.

Platelet granule disorders — “storage pool disease”

Rare disorders of platelet secretion, with variable reduction in the number and contents of:

• Alpha granules (α-SPD) — store fibrinogen and vWF
• Dense granules (δ-SPD) — store Ca²⁺, serotonin, ATP/ADP
• Rarely both (αδ-SPD)

The granule contents needed for clot formation (fibrinogen, vWF) and for further platelet activation (ADP) are simply not available. Hermansky-Pudlak syndrome = albinism + δ-SPD, with impaired release of granule-bound ADP. Molecular mechanisms are not well understood, bleeding is variable, and electron microscopy can detect the decreased granules.

Objective 2 · cascade recap

The classic cascade, as she frames it for the lab

Her caveat on the slide: this is only partly true in vivo. The two-pathway model is a description of the test tube, not of physiology — in a real vessel, tissue factor initiates and thrombin feeds back to amplify through F8 and F5.

Objective 2 · acquired

Vitamin K deficiency and liver disease

Vitamin K deficiency

• Usually hospitalized patients
• Cofactor for gamma-carboxylation of the vitamin K-dependent clotting proteins — 2, 7, 9, 10
• Malnutrition and decreased gut flora are usually responsible
• PT increases FIRST, because of the short half-life of factor 7
• Treatment: vitamin K replacement, with response in 24–48 hours

Urgent Coumadin reversal in a bleeding patient:

• Fresh frozen plasma (FFP) — contains ALL clotting factors
• Prothrombin complex concentrates — contain the 4 vitamin K-dependent factors

Liver disease

• Decreased synthesis of vitamin K-dependent factors
• Increased fibrinolysis, secondary to decreased antiplasmin
• Synthesis of abnormal fibrinogen
• Labs: increased PT and aPTT; decreased platelets with hypersplenism
• Treatment: FFP replacement when bleeding

Objective 2 · vWD

von Willebrand disease

The most common autosomally inherited bleeding disorder — estimated frequency around 1%, with no geographical or ethnic predilection. The VWF gene is on chromosome 12, cloned in 1985, and the protein undergoes extensive post-translational modification. Usually autosomal dominant transmission (types 1 and 2).

Bleeding is variable: epistaxis, spontaneous mucous membrane bleeding, excessive bleeding from wounds. Menorrhagia should prompt testing for vWD.

The factor VIII–vWF complex

• F8 is produced by endothelial cells in the liver and elsewhere — NOT by hepatocytes
• F8 binds vWF with high affinity, so if vWF levels are normal, all F8 circulates bound to vWF
• Since vWF stabilizes F8, vWF deficiency causes a secondary decrease in F8

Quantitative variants

• Type 1 — most common (65–85%). Autosomal dominant with variable expressivity, heterogeneous mechanisms. Decreased levels of normally functioning vWF (5–40%). Usually mild but heterogeneous in bleeding
• Type 3 — very rare but severe, with extremely low vWF. Can have hemarthrosis like severe hemophilia. Deletions or frameshift mutations produce either a null phenotype or a vWF that is not secreted

Qualitative variant

• Type 2 — 20–35%. Mostly missense substitutions causing defective multimer assembly. Produces structurally abnormal vWF that cannot interact normally with platelet GP1bα and F8. Mild to moderate bleeding. Many variants; Type 2A is most common

Laboratory evaluation

• aPTT — not elevated unless F8 is significantly decreased
• Platelet count normal, except low in type 2B
• vWF activity (ristocetin cofactor activity) — low in all types
• vWF antigen — corresponds to activity in types 1 and 3, but type 2 can have antigen higher than activity
• F8 activity — decreased
• vWF multimer studies — a gel study that can be helpful
• Genetics — useful in Type 3 for counselling; molecular tests exist for Type 2

Therapeutic management

• Replace vWF — VWF:F8 concentrate or recombinant vWF. Useful in all types, especially Types 3 and 2
• Stimulate release of vWF — DDAVP (desmopressin) releases vWF from endothelial Weibel-Palade bodies by agonist effect on vasopressin V2 receptors. Useful in Type 1, but check that it works in the individual patient
• Antifibrinolytics — Amicar, tranexamic acid. Inhibit conversion of plasminogen to plasmin, inhibiting fibrinolysis and thus stabilizing clots

Objective 2 · hemophilia

Hemophilia A and B

• Sex-linked (X-linked) recessive
• Hemophilia A (factor 8) — 1 in 5,000 males
• Hemophilia B (factor 9, “Christmas disease”) — 1 in 30,000 males
• Clinically indistinguishable from each other
• aPTT elevated, and a mixing study CORRECTS it — mixing normal plasma with patient plasma normalizes the aPTT
• Confirm with specific factor assays for F8 or F9
• Multiple genetic defects — >700 described for F8, >800 for F9

Severity tracks factor activity level

Factor products

Prepared from pooled human plasma or by recombinant techniques — F8 concentrates for hemophilia A, F9 concentrates for hemophilia B, and plasma-derived or recombinant VWF-F8 concentrates for vWD. Dosing depends on the situation, and the products are very expensive.

Factor 8 inhibitors

• Hemophilia A patients who have received F8 concentrates can develop an alloantibody that destroys F8
• Older patients can develop an autoantibody against F8 without having hemophilia
• Both bleed severely
• The mixing study does NOT correct — the inhibiting antibody rapidly binds and inactivates the F8 in the normal plasma you just added
• Inhibitor strength is estimated by the Bethesda titer

Treatment of an inhibitor:

• Large doses of F8 to overwhelm the inhibitor
• Recombinant 7a (NovoSeven) for high-titer inhibitors — activates X to Xa on the platelet surface, producing a “thrombin burst”
• Activated prothrombin complex concentrates — non-activated factors II, IX, X plus activated factor VII

Objective 3 · DIC

Disseminated intravascular coagulation

A “consumption coagulopathy” — consumption of platelets and clotting factors, with fibrin formation and subsequent lysis.

It can develop rapidly or slowly, and is classified as acute (uncompensated, with decreased clotting factors) versus chronic (compensated, with normal clotting factors).

Major associated disorders

• Obstetric complications — placental abruption, retained dead fetus, septic abortion, amniotic fluid embolism
• Infections — gram-negative sepsis, meningococcemia, Rocky Mountain spotted fever
• Neoplasms — widespread cancer, acute promyelocytic leukemia
• Massive tissue injury — trauma, burns
• Other — acute intravascular hemolysis, snakebites

Clinical manifestations

Signs are often masked by the underlying disorder.

• Bleeding is most common — ecchymoses, petechiae, purpura, trauma-related oozing, post-surgical hemorrhage (obstetric, trauma)
• Vascular thrombosis is less common, due to fibrin formation — renal insufficiency, necrotic skin lesions. More often seen when cancer is the underlying cause

Pathologic microvascular fibrin deposition — platelet-fibrin thrombi — causes the end-organ damage in DIC and in the other microangiopathies.

Laboratory manifestations

Management

Treat the underlying disease.

• Supportive care — vital signs, watch for bleeding and thrombosis, correct hypovolemia
• Follow labs — platelet count, PT, aPTT, D-dimer — to monitor the patient
• If bleeding, consider transfusing red cells, plasma, platelets, cryoprecipitate

Synthesis

Reading the panel — both bleeding lectures at once

Read it in three questions. Is the platelet count low? That splits quantitative from qualitative and vascular. Which clotting time is prolonged? Isolated PT points to F7 / vitamin K / warfarin; isolated aPTT points to F8, F9, F11, heparin, or an inhibitor; both point to the common pathway or consumption. Is fibrinogen low and D-dimer high? That is what makes it DIC rather than TTP or liver disease.

Highest yield

Seven things to carry out of this lecture

1. Petechiae mean platelets; hemarthrosis means factors. The bleeding pattern narrows the differential before any lab returns.
2. Qualitative platelet defects have a completely normal screening panel. Aspirin, Glanzmann, Bernard-Soulier, storage pool disease — normal count, normal PT, normal aPTT.
3. Glanzmann = GPIIb-IIIa = aggregation, no response to ADP/collagen/epinephrine. Bernard-Soulier = GP1b = adhesion, no response to ristocetin, with giant platelets.
4. PT rises first in vitamin K deficiency because F7 has the shortest half-life of factors 2, 7, 9, 10.
5. F8 is made by endothelial cells, not hepatocytes, and vWF stabilizes it — which is why vWF deficiency secondarily lowers F8 and can prolong the aPTT.
6. vWD antigen versus activity: they fall together in Types 1 and 3 (quantity), but antigen exceeds activity in Type 2 (quality). DDAVP for Type 1; concentrate for Types 2 and 3.
7. Mixing study corrects = factor deficiency; does not correct = inhibitor. And DIC is the one that moves every number — low platelets, low fibrinogen, prolonged PT and aPTT, high D-dimer.

Approach

Component therapy, not whole blood

The governing principle is that a patient receives only the part of blood they actually need, in the correct amount, guided by evidence-based thresholds. Three reasons drive this:

• Every transfusion carries risk — the risk/benefit ratio must be weighed each time
• The blood supply is limited; one donation split into components serves several patients
• Alternatives should be used when possible

Blood comes from healthy, volunteer, non-paid donors screened by questionnaire for infectious-disease risk factors, and informed consent is required from the patient before transfusing.

FDA-required testing on every unit

• HIV-1 and HIV-2 — nucleic acid amplification (NAT) plus antibodies
• Hepatitis C — NAT plus antibodies · Hepatitis B — NAT, HBsAg, anti-HBc
• HTLV I and II, syphilis (Treponema pallidum), West Nile virus (NAT)
• Trypanosoma cruzi (Chagas disease), CMV (some units), Babesia (endemic areas)

Objective 1 · the products

The five components and what each one is for

Red cell transfusion thresholds

Symptomatic anemia is its own indication regardless of where the number falls — excessive fatigue, malaise, headache, tachycardia, hypotension, end-organ damage.

Platelet transfusion “triggers”

Objective 2 · ABO

ABO — the system that kills you fastest

The most important system for transfusion compatibility. ABO antigens are carbohydrate, determined by which saccharide is attached to a subterminal galactose. The A and B transferase genes encode enzymes that covalently attach that sugar:

The H antigen (fucose) is the backbone onto which A and B are built. Absence of H entirely is the Bombay phenotype, and those individuals make anti-H — which makes them incompatible with essentially all ordinary donors, including group O.

Selecting ABO group for red cell transfusion

Read the table as a rule rather than a list: a recipient can receive any group whose antigens they will not attack. Group O has no A or B antigen, so O is the universal red cell donor; group AB has no anti-A or anti-B, so AB is the universal recipient. Rh(D) positive = 85% of the population, Rh(D) negative = 15%.

Objective 2 · Rh

Rh — second in importance, different in kind

• Protein-based antigens, function unclear — in contrast to the carbohydrate ABO antigens
• Coded by 3 allelic antigen pairs: RHD codes the D antigen; RHCE codes C/c and E/e
• Antibodies against D, C, c, E, e are caused by exposure — transfusion, pregnancy, transplant
• RhoGAM (Rho(D) immune globulin) prevents formation of anti-D in Rh(D)-negative pregnant women

Where red cell antibodies come from

• Alloantibody — the individual was exposed to a foreign RBC antigen during transfusion or pregnancy and made an antibody against it
• Hemolytic disease of the newborn — mother produces antibody against a foreign fetal RBC antigen (Rh system, Kell); the IgG crosses the placenta, binds fetal RBCs, and destroys them

RBC antigens associated with disease

Objective 3

Tests performed in the blood bank before transfusion

Three steps, in order — type, screen, crossmatch.

Methods include classic tube typing, and automated solid-phase capture and gel systems.

What counts as a “clinically significant” antibody

• ABO — preformed anti-A, anti-B
• Rh system — D, C, c, E, e
• Others — Kell, Kidd, Duffy, S

Objective 4 · acute

Transfusion reactions — the immediate ones

Her definition: any unexpected or unfavorable sign or symptom occurring during or shortly after transfusing blood or one of its components. Two rules sit above everything else:

Acute hemolytic transfusion reaction (AHTR)

• Most are due to ABO incompatible transfusion; the most common single scenario is “A to O” — group A blood given to a group O patient
• Preformed antibody (anti-A in the recipient) binds antigen on the transfused cells → complement fixation → C5b-9 MAC → intravascular hemolysis
• Presentation: fever, chills, hypotension, back pain, tachycardia, diaphoresis, dyspnea
• Treatment: stop the transfusion; maintain urine output with fluids and diuretics; cardiovascular support in the ICU

Febrile nonhemolytic transfusion reaction (FNHTR)

• Patient receiving red cells, platelets, or FFP develops fever (>1°C rise) and shaking chills during or shortly after transfusion
• Common — up to 1 in 100 to 1 in 200 transfusions
• Mechanism: cytokines are transfused with the product and disrupt the thermoregulatory center in the brain
• Not life threatening
• Treatment: stop transfusing; acetaminophen for fever, meperidine (Demerol) for rigors

Allergic reactions

• Pruritus and/or urticaria WITHOUT fever, possibly with wheezing (bronchospasm)
• Mechanism: recipient IgE antibodies recognize an allergen contained in the transfused unit
• Anaphylaxis is rare but does occur — classically in patients with IgA deficiency
• Antihistamines for treatment and for prevention (pre-medication)

Objective 4 · the rest

TRALI, TACO, TA-GVHD, and septic reactions

Transfusion-related acute lung injury (TRALI)

• During transfusion the patient develops acute respiratory distress — tachypnea, dyspnea, fever, hypoxemia — requiring intubation
• Majority associated with granulocyte antibodies or HLA antibodies in the donor that react with patient white cells; neutrophil activation leads to lung injury
• Treatment is aggressive respiratory support in the ICU
• Used to be the most commonly reported cause of transfusion death; risk decreased by limiting plasma sources to males, never-pregnant females, and females tested for HLA antibodies

Transfusion-associated circulatory overload (TACO)

Her illustration is arithmetic rather than immunologic: 2 units of red cells at 325 mL, plus 3 units of FFP at 225 mL, plus maintenance IV fluids at 75 mL/hr, in an older patient with impaired cardiovascular status, sums to cardiac failure with pulmonary compromise — and diuretics are needed.

Transfusion-associated graft-versus-host disease (TA-GVHD)

• Rare but almost always fatal due to immunosuppression
• Occurs in immunosuppressed patients — cancer, NICU
• Onset 8–10 days post-transfusion: marked pancytopenia with marrow aplasia, fever, rash on face and trunk spreading to extremities, mucositis, nausea/vomiting/diarrhea, hepatitis
• Mechanism: recipient shares a haplotype with an HLA homozygous donor, allowing donor lymphocytes to proliferate and attack the recipient. Higher risk with donations from relatives.
• Prevention: irradiate cellular blood products (red cells, platelets, granulocytes). Irradiation inactivates T-lymphocytes by crosslinking DNA and is 100% effective.

Septic transfusion reactions

• Bacteria enter the product because they were in the donor or the unit was contaminated during collection or processing
• Can cause fatal septicemia with high fever and profound hypotension
• More common in platelets than red cells — because platelets are stored at room temperature
• Platelets are now tested for bacteria or treated to kill bacteria

Objective 5

Alternatives to blood component therapy

• Autologous transfusion
  • Preoperative autologous donation — the patient banks their own blood before elective surgery
  • Blood salvage — “cell savers” suction blood from the wound, wash it, and return the RBCs to the patient
• Hematopoietic growth factors
  • Erythropoietin (EPO) → red cells
  • G-CSF (granulocyte colony stimulating factor) → white cells
  • Thrombopoietin mimetics → platelets

Synthesis

Sorting a reaction at the bedside

Work it in three questions. Is there fever? No fever with hives is allergic; no fever with volume overload is TACO. How fast? Minutes with back pain and hypotension is hemolytic; eight to ten days with pancytopenia is TA-GVHD. Which product and is there hypoxia? Platelets with profound hypotension suggests sepsis; hypoxia requiring intubation without volume overload is TRALI.

Highest yield

Eight things to carry out of this lecture

1. Acute intravascular hemolytic transfusion reactions are caused by transfusing the wrong blood to the wrong patient. The failure is patient identification, not serology — which is why mislabeled tubes are never accepted.
2. ABO is carbohydrate, IgM, preformed, and intravascular. Rh is protein, IgG, requires exposure, and crosses the placenta. Nearly every difference between the two systems follows from those two lines.
3. First step in any suspected reaction is to STOP THE TRANSFUSION. Everything else comes second.
4. Ask why the platelet count is low before transfusing platelets. In DIC, ITP, TTP, and HIT platelet transfusion is not helpful, and in HIT it feeds the thrombosis.
5. Cryoprecipitate is a fibrinogen product — hypofibrinogenemia, dysfibrinogenemia, F13 deficiency. Despite containing F8 and vWF it should NOT be used for hemophilia A or vWD.
6. FFP contains all clotting factors: DIC and liver disease, TTP (supplies ADAMTS-13), and Coumadin reversal (supplies 2, 7, 9, 10).
7. TRALI is lung injury from donor antibodies; TACO is volume overload. Both cause respiratory distress; only TACO responds to diuretics.
8. TA-GVHD is prevented 100% by irradiating cellular products, and the risk is higher from relatives because HLA similarity lets donor lymphocytes survive.

Framework

One stem cell, every lineage

All blood and marrow elements arise by stepwise maturation from a hematopoietic stem cell (HSC). Two features define the HSC and both are testable:

• Pluripotent — it can become any blood lineage
• Capable of self-renewal — it replaces itself, so the pool is never exhausted

Under normal circumstances this happens predominantly in the bone marrow. Two exceptions you already know:

Reference ranges — absolute counts (×10³/µL, Robbins)

Reference ranges vary by laboratory and by patient age. Leukopenia is a decreased WBC count; leukocytosis is an increased WBC count. Either can involve multiple cell lines or just one.

Objective 2 · leukopenia

Neutropenia and agranulocytosis

Decreased circulating neutrophils. Every cause falls into one of two buckets — decreased production or increased use/consumption.

Objective 2 · leukopenia

Lymphopenia

• T cells represent 80–90% of circulating lymphocytes, so T-cell damage or loss contributes more to lymphopenia than B-cell loss does
• Immunodeficiencies — DiGeorge syndrome, HIV
• Increased cortisol — steroid use, Cushing syndrome
• Autoimmune disorders
• Whole body radiation

Objective 2 · HLH

Hemophagocytic lymphohistiocytosis (HLH)

A systemic inflammatory syndrome caused by increased cytokines and inflammatory mediators released from macrophages and cytotoxic T cells.

Clinical and laboratory criteria

• Fever and hepatosplenomegaly
• High ferritin — often strikingly so
• Elevated soluble IL-2 receptor
• Decreased NK cell activity
• Hemophagocytosis — macrophages ingesting blood cells, the finding the disease is named for

Triggers, course, and therapy

• Familial and sporadic forms both exist
• Most common trigger is infection, often EBV; also underlying malignancy
• Poor prognosis — hepatitis, disseminated intravascular coagulation (DIC), organ failure, death
• Therapy is immunosuppression and chemotherapy

Objective 3 · leukocytosis

Neutrophilia, lymphocytosis, and the other lineages

A wide variety of benign/reactive and some neoplastic conditions raise the white count. Sort by which line is up.

Objective 3 · leukocytosis

Infectious mononucleosis

• Most commonly acute Epstein-Barr virus; less often cytomegalovirus (CMV)
• Transmitted by saliva — the “kissing disease”
• EBV infects B cells, oropharyngeal epithelial cells (→ pharyngitis), and hepatocytes (→ hepatitis)

Diagnosis

• Monospot test — a screening assay detecting IgM heterophile antibodies that cross-react with horse or sheep red cells, causing agglutination
• Negative in CMV-associated IM
• May be negative in the first few days after infection — the window period
• EBV-specific serology for antibodies against the viral capsid antigen when the monospot is unhelpful

Prognosis and complications

• Most cases resolve without complications
• Splenomegaly → increased risk of splenic rupture
• Drug rash on exposure to ampicillin or penicillin
• After exposure the virus remains dormant in memory B cells — risk of reactivation and EBV-driven lymphomas if the patient later becomes immunocompromised

Objective 3 · the two “-oid” pictures

Leukemoid reaction vs leukoerythroblastosis

Both are leukocytosis with immature cells in the blood, and the entire point is telling them apart — from each other, and from real leukemia.

Objectives 4–5 · lymph node

Reactive lymph node patterns

Lymphadenopathy is enlarged lymph nodes. Benign enlargement is most commonly one of three histologic patterns, and each one maps to a different compartment of the node and a different stimulus.

Objective 5 · lymphadenitis

Acute vs chronic lymphadenitis

Highest yield

Eight things to carry out of this lecture

1. HSCs give rise to all other hematopoietic cells in an orderly manner, and their two defining features are pluripotency and capacity for self-renewal.
2. Drug toxicity is the most common cause of neutropenia/agranulocytosis — dose-dependent with chemotherapy, idiosyncratic with certain antibiotics and psychiatric medications. Infection risk climbs sharply below 0.5 ×10³/µL.
3. HLH is a systemic inflammatory syndrome that causes cytopenias — cytokines from macrophages and cytotoxic T cells suppress hematopoiesis. Look for fever, hepatosplenomegaly, very high ferritin, elevated soluble IL-2 receptor, decreased NK activity, and hemophagocytosis; the most common trigger is infection, often EBV.
4. Infections are the most common cause of leukocytosis — bacterial → neutrophilia, viral → lymphocytosis. The exception that gets tested is Bordetella pertussis, a bacterium causing lymphocytosis by blocking lymphocyte egress from the circulation.
5. IM is associated with a prominent CD8-positive cytotoxic T-cell reaction. EBV infects B cells, but the atypical lymphocytes are reactive T cells and the splenomegaly is PALS hypertrophy.
6. A negative monospot does not rule out IM — it is negative in CMV-associated disease and during the window period. Confirm with EBV viral capsid antigen serology.
7. Leukemoid reaction = leukocytosis with circulating immature granulocytes, commonly infectious, often with toxic changes, and lacking eosinophilia, basophilia, and nucleated red cells. Leukoerythroblastic reaction = the same left shift PLUS circulating red cell precursors, typically without toxic changes, and usually signals a marrow process.
8. Lymphadenopathy sorts by compartment and by pain. Follicular hyperplasia is B-cell driven, paracortical is T-cell/viral, sinus histiocytosis drains tumors and chronically inflamed sites. Acute lymphadenitis is painful and infectious; chronic lymphadenitis is painless and raises concern for chronic inflammation or neoplasia.

Framework

The 20% blast rule — what makes a leukemia “acute”

Acute leukemia is generally defined by ≥20% blasts in the blood or bone marrow. That single number is the dividing line, and almost everything else in this lecture hangs off it.

Blasts are the immature cells that arise from the hematopoietic stem cell. They can be undifferentiated, lymphoid, and/or myeloid. Chronic leukemias sit on the other side of the line: they are composed of more mature hematopoietic cells.

The two chronic counterparts to keep straight:

• Chronic lymphocytic leukemia — composed of mature B lymphocytes
• Chronic myeloid leukemia — composed of various maturing myeloid cells, with <20% blasts

Clinical

Presentation — the marrow is being crowded out

Patients present with features related to the lack of normal hematopoiesis, because the blasts replace the normal marrow cells. Each cytopenia maps to a symptom:

The white count itself is not reliable in either direction. Patients often present with leukocytosis from numerous circulating blasts, but some cases present with pancytopenia instead.

Workup

Four diagnostic modalities, and why one is never enough

Diagnosing and categorizing an acute leukemia requires numerous modalities used together:

ALL

Acute lymphoblastic leukemia — the overview

• Most common childhood cancer
• A minority of adult leukemias
• The majority are B-ALL (~85%), presenting with extensive blood and bone marrow involvement
• T-ALL typically presents in adolescent boys with a mediastinal/thymic mass — that is, it is more likely to have a lymphomatous presentation

B-ALL

B-lymphoblastic leukemia — clinical, diagnosis, prognosis

Also called B-ALL, BLL, or precursor B-cell leukemia.

Clinical

• Often presents with bone pain/tenderness
• More likely to involve the CNS than T-ALL

Diagnosis

• ≥20% blasts — though in practice usually upwards of 80–90%
• Blasts express CD10, CD19, TdT, and CD34 by flow cytometry or immunohistochemistry
• TdT = terminal deoxytransferase, a DNA polymerase expressed by both B- and T-lymphoblasts
• CD34 = stem cell antigen — positive in both ALL and AML
• B and T lymphoblasts are morphologically identical

Prognosis

Highly curable in children (85–90%) versus a minority of adults (30–40%).

T-ALL

T-lymphoblastic leukemia

• Blasts are positive by flow/IHC for a variety of T-cell markers (CD1a–CD8), plus TdT and CD34
• Slightly poorer prognosis than B-ALL — 70–80% cure

AML

Acute myeloid leukemia — clinical and diagnosis

• Predominantly affects adults
• An extremely heterogeneous disease, reflecting the complexities of myeloid differentiation

The WHO classifies AML into 2 general groups:

Diagnosis

• ≥20% blasts
• Most cases express the common myeloid antigens CD33, CD117, MPO, and CD34
• Some myeloid blasts have identifiable aggregates of MPO in their cytoplasm → Auer rods

AML group 1

AML with defining genetic abnormalities

Two categories of lesion define this group, and each carries its own prognosis:

APL

Acute promyelocytic leukemia — the one with an antidote

• Defined by the t(15;17); PML::RARA translocation
• Proliferation of abnormal promyelocytes
• Morphology: bilobed “apple-core” / “sliding plate” nucleus, heavy granulation, and faggot cells (bundled Auer rods). The bilobed nucleus is simply where promyelocytes normally get stuck in development
• Blasts are CD34 negative, and positive for MPO, CD33, and CD117
• Numerous cytoplasmic granules contain procoagulants → DIC
• RARA = retinoic acid receptor alpha, and therapy is all trans retinoic acid (ATRA)

Poor-prognosis AML

AML, myelodysplasia-related (AML-MR) and secondary AML

These two are grouped together because they share a profile: complex karyotype and very poor prognosis.

AML group 2

AML defined by differentiation

• Similar to the historic FAB classification (M0–M7)
• Eight subtypes with various morphologic and immunophenotypic criteria
• Functions as the “wastebasket” for all AMLs not otherwise defined by clinical history or cytogenetics

Two subtypes are singled out as high yield:

Highest yield

Ten things to carry out of this lecture

1. ≥20% blasts in blood or bone marrow defines acute leukemia. Chronic leukemias are composed of more mature cells — CLL = mature B lymphocytes, CML = maturing myeloid cells with <20% blasts.
2. Presentation reflects failure of normal hematopoiesis as blasts replace the marrow: anemia → fatigue, neutropenia → infection, thrombocytopenia → mucosal bleeding and petechiae. Leukocytosis is common, but some cases present with pancytopenia.
3. Diagnosis requires four modalities — morphology, flow cytometry, cytogenetics (karyotype and FISH), and molecular/NGS — because B and T lymphoblasts are morphologically identical.
4. ALL is the most common childhood cancer; ~85% is B-ALL with extensive blood and marrow involvement, while T-ALL presents in Teenagers with a Thymic mass.
5. B-ALL blasts are CD10, CD19, TdT, CD34 positive. TdT marks both B- and T-lymphoblasts, and CD34 is positive in both ALL and AML — neither is a lineage marker.
6. B-ALL good prognosis: hyperdiploidy (>50 chromosomes), t(12;21) ETV6::RUNX1, age >1 and <10. Poor: hypodiploidy, t(9;22) BCR::ABL1, white count >100K at presentation. Curable in 85–90% of children versus 30–40% of adults.
7. AML predominantly affects adults, requires ≥20% blasts, and usually expresses CD33, CD117, MPO, CD34. Auer rods are aggregates of MPO and are ONLY present in myeloid blasts.
8. Among AML with defining genetic abnormalities, t(8;21), inv(16), t(15;17), and mutated NPM1 are favorable; t(9;11) KMT2A(MLL) is poor.
9. APL is defined by t(15;17); PML::RARA, is CD34-negative but MPO/CD33/CD117 positive, causes DIC because its granules contain procoagulants, and is treated with ATRA.
10. AML-MR and secondary (therapy-related) AML both carry a complex karyotype and very poor prognosis. Among AML defined by differentiation, monocytic leukemia gives gingival involvement and megakaryoblastic leukemia associates with Down syndrome in early childhood — both MPO-negative.

Placement

Where MDS sits among the chronic myeloid neoplasms

Everything in this lecture lives on the chronic side of the 20% blast line. There are three categories of chronic myeloid neoplasm, and they are distinguished first by the peripheral blood count, then further defined by marrow morphology and genetic alterations.

Definition

What MDS actually is

• A clonal stem cell disorder
• Maturation defects → ineffective hematopoiesis
• Primary (de novo, idiopathic) versus secondary (therapy-related, or with germline predisposition)

Epidemiology

Who gets it, and how it is found

• Average age of onset is 70
• Usually an incidental CBC finding; can present with symptoms related to the cytopenias — fatigue, bruising/bleeding, infections

Pathogenesis is unknown in most cases, though some is attributable to prior cytotoxic chemotherapy. There is no single driver mutation or cytogenetic abnormality present across the board. The recurrent cytogenetic abnormalities are:

Morphology

Dysplasia in the three myeloid lineages

MDS is characterized by morphologic dysplasia, and it requires >10% dysplastic cells in a given lineage for that lineage to count as dysplastic.

Prognosis

Risk stratification and progression to AML

The WHO subclassifies MDS into those with defining genetic abnormalities and those that are morphologically defined. Prognostic score is assigned from three inputs:

• 10–40% of patients with MDS will progress to AML
• Complex cytogenetics and increased blasts portend a poorer prognosis
• MDS after cytotoxic therapy has the highest risk of progression to AML and the most rapid clinical course
• Increased blasts means ≥5% in the marrow and/or ≥2% in the peripheral blood; ≥20% is AML
• Survival ranges from 5+ years in low-risk subtypes to under 1 year in high-risk subtypes; most patients succumb to complications of their cytopenias

Therapy

Treatment follows fitness, not just risk

Highest yield

Carry-out points

1. MDS is characterized by ineffective hematopoiesis — manifesting clinically as cytopenias and morphologically as a hypercellular marrow with dysplasia.
2. Common cytogenetic abnormalities are −5/del(5q), −7/del(7q), and complex karyotype (≥3 aberrations).
3. Dysplasia requires >10% of cells in a lineage: megakaryocytic hypolobation and pawn-ball forms, erythroid nuclear budding and ring sideroblasts, granulocytic pseudo-Pelger-Huët and hypogranulation.
4. MDS is a disease of older adults (average onset 70) and all subtypes carry a risk of progression to AML, at 10–40%.
5. MDS after cytotoxic therapy has the most aggressive course and the highest rate of progression to AML.
6. Therapy is allogeneic transplant in younger patients, and supportive plus hypomethylating agents in those not amenable to transplant.

Framework

The shared profile of a myeloproliferative neoplasm

Primarily a disease of adults, 40–60 years of age. The molecular lesion in every case is a tyrosine kinase mutation producing constitutive activation, and the consequence is that one or more hematopoietic lineages are expanded.

Genetics

The mutation table

CML

Chronic myeloid leukemia — genetics and course

• 90–95% have t(9;22)(q34.1;q11.2) — the BCR gene on chromosome 22 joined to the ABL1 gene on chromosome 9. Others carry variant translocations and are detected by FISH and RT-PCR
• BCR breakpoints: Major (exons 12–16) → p210; μ-BCR (exons 17–20) → p230; Minor (exons 1–2) → p190
• 50% are asymptomatic at diagnosis, found on an abnormal WBC count; 50% have splenomegaly
• Phases: chronic phase and blast phase; fewer than 5% are in blast phase at diagnosis
• Untreated, progression to blast phase takes about 3–5 years; with TKI therapy (imatinib or a later generation agent), 80–95% five-year overall survival

CML

Chronic phase — blood and marrow

CML

Adverse risk features and blast phase

PV

Polycythemia vera

• Increased red cell production independent of normal regulation, with a decreased erythropoietin
• Most patients have JAK2 V617F, a gain-of-function mutation
• Phases: polycythemic phase and spent phase (post-polycythemic myelofibrosis)
• Must exclude secondary erythrocytosis, heritable polycythemia, and other MPNs
• Median age 60, slight male predominance; spleen and liver commonly affected
• Hyperviscosity — headache, dizziness, visual disturbance, hypertension
• Thrombosis in 20–25%, arterial or venous — mesenteric, portal, or splenic vein, and Budd-Chiari syndrome (hepatic vein thrombosis)
• Itching, attributed to mast cell activation
• Treatment is phlebotomy or hydroxyurea

PV

Blood, marrow, and the spent phase

Prognosis: with treatment, median survival exceeds 10 years. Most patients die of thrombosis, hemorrhage, or secondary malignancy. Patients treated with cytotoxic agents have an increased risk of MDS and AML — 10–20% versus 2–3%. Increased marrow fibrosis at diagnosis predicts more rapid progression.

ET

Essential thrombocythemia

• Sustained thrombocytosis >450 ×10&sup9;/L, predominantly involving the megakaryocyte lineage
• Leukocytosis and erythrocytosis are not typical
• Increased large mature megakaryocytes — large to giant with hyperlobated, “staghorn-like” nuclei
• Slight female predilection; most patients 50–60, with a second peak in the 30s, predominantly women
• About 50% asymptomatic at diagnosis; 50% have vascular occlusion or hemorrhage, including Budd-Chiari syndrome
• Mild splenomegaly may be present; less risk of hyperuricemia than other MPNs
• Indolent — 10–15 year median survival; some progress to post-ET myelofibrosis; fewer than 5% transform to blast phase or MDS, and that may be related to cytotoxic therapy

PMF

Primary myelofibrosis

• 30% of patients are asymptomatic; adults 60–70 years of age
• Often found as unexplained splenomegaly on examination, or on routine blood work showing isolated thrombocytosis, or anemia with leukocytosis and/or thrombocytosis
• Bone marrow biopsy is essential for diagnosis; organomegaly of spleen and liver
• Two phases: prefibrotic/early stage and overt fibrotic stage

Prognosis is variable: median survival 3–7 years when diagnosed in the fibrotic phase versus 10–15 years in the prefibrotic phase. Complications include marrow failure with infection and hemorrhage, thrombosis, cardiac failure, and hypertension. Progression to blast phase occurs in 5–30%, a subset related to prior cytotoxic therapy.

Workup

Diagnostic approach to a suspected MPN

Highest yield

Carry-out points

1. MPNs are adult diseases driven by a constitutively active tyrosine kinase, producing cytoses with a hypercellular marrow, normal maturation, and blasts not increased.
2. BCR::ABL1 is present in 100% of CML and must be excluded first; JAK2 V617F is present in >95% of PV; ET and PMF share JAK2/CALR/MPL and cannot be separated by mutation alone.
3. CML chronic phase shows a left-shifted neutrophilia with absolute basophilia and eosinophilia, blasts <5%, and dwarf megakaryocytes. Basophilia distinguishes it from a leukemoid reaction.
4. Blast phase of CML is ≥20% blasts; 10–19% blasts and ≥20% basophils are adverse features short of that.
5. PV is autonomous red cell production with a subnormal erythropoietin, thrombosis in 20–25% including Budd-Chiari, and pruritus; treatment is phlebotomy or hydroxyurea.
6. ET is sustained thrombocytosis >450 ×10&sup9;/L with large staghorn megakaryocytes and an indolent course of 10–15 years.
7. PMF requires a marrow biopsy, progresses from a prefibrotic to an overt fibrotic stage, and produces teardrop cells, a leukoerythroblastic smear, and extramedullary hematopoiesis.
8. All four can enter a spent, fibrotic, or blast phase; cytotoxic therapy raises the risk of transformation to MDS/AML.

Origin

B-cell development maps onto B-cell neoplasia

B-cell neoplasms often arise from cells arrested at a certain stage of development. That arrest produces a clonal proliferation of cells expressing CD markers that mirror the normal cell at that stage — which is why the immunophenotype identifies the disease.

Definitions

Leukemia, lymphoma, and clonality

• The WHO defines more than 40 types of mature B-cell neoplasm
• “Non-Hodgkin” lymphoma = every lymphoma except classic Hodgkin lymphoma and nodular lymphocyte-predominant Hodgkin lymphoma
• Leukemia = involving blood and bone marrow; Lymphoma = involving lymph nodes and/or extranodal soft tissue
• Many B-cell neoplasms classically present as one or the other, but nearly all can involve both
• Diagnosis and prognosis rest on immunophenotype / cell of origin and genetics, not the site of involvement

Clonality separates neoplasm from reaction:

B-cell clonality is assessed by sequencing the Ig genes, by surface light chain restriction on flow cytometry, or by genetic abnormalities.

Risk

Epidemiology and infectious associations

Predominantly affects adults and elderly patients, and most patients have no known risk factor. Recognized risks are primary immunodeficiency syndromes, autoimmune disorders (Hashimoto thyroiditis, Sjögren syndrome — associated with MALT lymphomas), and acquired immunodeficiency (HIV, iatrogenic immunosuppression in transplant patients).

Approach

Diagnosis by size, phenotype, and genetics

Phenotype is assessed by immunohistochemistry on formalin-fixed tissue and by flow cytometry on fluids and fresh tissue. Genetics uses cytogenetics (karyotype, FISH) and molecular testing for gene mutations.

CLL/SLL

Chronic lymphocytic leukemia / small lymphocytic lymphoma

• CLL and SLL are the SAME disease, named by where it is found — blood and marrow only = CLL (the majority); tissue only = SLL (the minority). Many patients are both
• Most common leukemia of adults, usually in older patients
• Discovered incidentally, on a routine CBC showing elevated WBC with lymphocytosis
• Cell of origin is a naïve B cell
• Smear: small lymphocytes with very clumpy chromatin and smudge / basket cells

Prognosis: indolent and incurable. Complications include autoimmune hemolytic anemia and hypogammaglobulinemia with reduced normal immunoglobulins leading to infections. Transformation occurs as prolymphocytic progression (10–30%) or Richter syndrome → DLBCL, which presents clinically as rapidly enlarging lymph nodes in a patient with known CLL/SLL.

Hairy cell

Hairy cell leukemia

• Rare — about 2% of lymphoid leukemias; middle-aged to elderly, M>>F
• Involves bone marrow, peripheral blood, and spleen — not associated with lymphadenopathy
• Patients present with splenomegaly and pancytopenia, notably including monocytopenia
• Blood: hairy cells. Marrow: diffuse infiltrate of small lymphocytes with “fried egg” morphology and reticulin fibrosis. Spleen: red pulp involvement with blood lakes
• Essentially 100% of cases carry a BRAF V600E mutation
• Very sensitive to interferon alpha and purine analogues such as cladribine; many obtain durable remission, though relapse occurs, and BRAF inhibitors and salvage chemotherapy are available

FL

Follicular lymphoma

• Second most common lymphoma after DLBCL, roughly 20%; middle-aged to older adults
• Asymptomatic with enlarged nodes; widespread at diagnosis with a waxing and waning clinical course
• Genetics: t(14;18) — BCL2 (chromosome 18) to IGH (chromosome 14), placing BCL2 under IGH promoter control and causing overexpression of BCL2, an anti-apoptotic molecule normally NOT expressed in germinal centers. Detected by FISH or karyotype
• Cell of origin is a germinal center B cell
• Prognosis: low grade (1–3A) is indolent and incurable, median survival 7–8 years; grade 3B is aggressive and potentially curable, treated like DLBCL; transformation to DLBCL in 25–35%, with gain of additional chromosomal abnormalities and short survival thereafter

MCL

Mantle cell lymphoma

• Older adults, M>>F; usually asymptomatic with enlarged lymph nodes
• High stage at diagnosis — involves lymph nodes, bone marrow, spleen, and extranodal sites, with peripheral blood in about 20%; may produce lymphomatoid polyposis of the bowel
• Genetics: t(11;14) — CCND1 (chromosome 11) to IGH (chromosome 14), causing overexpression of Cyclin D1, a cell-cycle/proliferative molecule. Detected by FISH or karyotype
• Cell of origin is a naïve, pre-germinal center B cell
• The EXCEPTION to the indolent nature of small B-cell lymphomas — incurable and aggressive, but still too slowly growing to respond to intensive chemotherapy; roughly 3–5 year survival
• No Richter transformation — more aggressive histologic variants exist but remain mantle cell lymphoma rather than transforming to DLBCL

MZL

Marginal zone lymphoma and MALT lymphoma

• About 10% of all lymphomas, with nodal, splenic, and extranodal varieties — the extranodal form being MALT lymphoma, of mucosa-associated lymphoid tissue
• Older adults; involves mucosal and epithelial sites — stomach, eye, skin, thyroid, salivary gland
• Gastric MALT lymphoma is the most common, with an H. pylori association; triple therapy is often curative UNLESS the lymphoma carries t(11;18)
• Arises from post-germinal center cells in the marginal zone that infiltrate the nearby follicles
• Translocations vary by site; t(11;18) (BIRC3::MALT1) is associated with gastric MALT

LPL

Lymphoplasmacytic lymphoma and Waldenström macroglobulinemia

• 1–2% of lymphomas, in older adults
• Arises from a late post-germinal center lymphocyte; the neoplastic population is a mixture of lymphocytes, plasmacytoid lymphocytes, and plasma cells
• No recurrent chromosomal abnormalities, but a MYD88 L265P mutation is present in >90%

Burkitt

Burkitt lymphoma — the intermediate-size lymphoma

• Aggressive, highly proliferative neoplasm that is very responsive to intensive chemotherapy
• Patients are at very high risk of tumor lysis syndrome; rapidly fatal if untreated
• Can present with leukemic involvement
• Morphology: “starry sky”; Cytogenetics: t(8;14) — IGH::MYC, MYC being an oncogene

DLBCL

Diffuse large B-cell lymphoma

• Most common lymphoma in the world
• A very heterogeneous group — the WHO recognizes more than ten large B-cell lymphomas, but DLBCL, not otherwise specified (NOS) is the most common
• De novo disease presents in older adults with rapidly enlarging localized lymphadenopathy or organomegaly
• Can also arise by transformation from a lower-grade process — CLL/SLL or follicular lymphoma
• Aggressive and fatal if untreated; requires intensive chemotherapy for cure, with roughly 70% remission and 40% cure. Prognosis improved with the addition of rituximab, an anti-CD20 antibody

Highest yield

Carry-out points

1. B-cell neoplasms arise from various stages along normal B-cell development and are clonal.
2. Leukemia = peripheral blood involvement; lymphoma = lymph node/tissue involvement — but most B-cell neoplasms can be both, so classification rests on phenotype and genetics rather than site.
3. B-cell lymphomas are categorized by cell size, and most small B-cell lymphomas are indolent — the exception is mantle cell lymphoma.
4. Indolent lymphomas are incurable; aggressive lymphomas are potentially curable, because chemotherapy kills dividing cells.
5. Burkitt lymphoma comes in three flavors — endemic, sporadic, and immunodeficiency-related — with starry sky morphology and MYC rearrangement.
6. DLBCL is heterogeneous, arises de novo or by transformation, and is responsive to intensive chemotherapy with possible cure.

Definition

What a plasma cell neoplasm is

A clonal proliferation of terminally differentiated B cells — plasma cells — that secrete monoclonal immunoglobulin, in the order IgG > IgA > light chain only.

• Immunoglobulin accumulates in serum and is detected on serum protein electrophoresis as the M-spike. M-spike = monoclonal Ig = paraprotein
• Immunoglobulin eliminated in the urine is the Bence-Jones protein
• An IgM-secreting lymphoproliferative disorder is Waldenström macroglobulinemia = lymphoplasmacytic lymphoma, not myeloma

The family of plasma cell neoplasms comprises MGUS, immunoglobulin-related (AL) amyloidosis, heavy chain disease, plasma cell myeloma / multiple myeloma, and plasmacytoma.

Myeloma

Multiple myeloma — epidemiology and pathogenesis

• Characterized by multifocal osteolytic lesions
• Accounts for about 1% of malignant tumors and 10–15% of all hematopoietic neoplasms
• Male > female (1.5:1), and twice as frequent in African Americans as in whites
• Rare under 50; peak incidence 65–70 years

Etiology and pathogenesis: exposure to toxins and radiation, chronic antigenic stimulation, and IGH gene rearrangement. IL-6 promotes expansion and survival of myeloma cells. Factors produced by the myeloma cells — MIP1α, TNF, IL-1β — activate osteoclasts via RANK.

CRAB

Clinical features and laboratory findings

Patients also suffer infections due to immune deficiency. Serum and urine assessment for M-protein is essential for diagnosis and follow-up, serving as a tumor marker.

Laboratory and pathologic findings: serum protein electrophoresis showing an M-spike; rouleaux on the peripheral smear; bone marrow biopsy showing a plasma cell infiltrate; and flow cytometric analysis demonstrating a clonal population.

MGUS

Monoclonal gammopathy of undetermined significance

• A pre-neoplastic condition
• M-spike identifiable on serum protein electrophoresis, <3 g/dL
• Patients are asymptomatic and have <10% monoclonal plasma cells in the bone marrow
• 1% progress to plasma cell myeloma

Light chains

Light chain deposition disorders

Highest yield

Carry-out points

1. Plasma cell neoplasms are clonal proliferations of immunoglobulin-secreting plasma cells, most often IgG > IgA > light chain only.
2. Symptoms follow the secretion and accumulation of monoclonal protein — M-spike in serum and Bence-Jones protein in urine.
3. Multiple myeloma is the most important plasma cell neoplasm, defined by multiple lytic lesions and the CRAB criteria — hyperCalcemia, Renal insufficiency, Anemia, Bone lesions.
4. MGUS is an M-spike under 3 g/dL without symptoms and with under 10% monoclonal plasma cells in the marrow, progressing to myeloma in about 1%.
5. Free light chains cause AL amyloidosis when they deposit in tissue and myeloma kidney when they deposit in tubules.
6. An IgM monoclonal gammopathy is Waldenström macroglobulinemia / lymphoplasmacytic lymphoma, not myeloma.

Context

Where T-cell lymphomas sit in the overall distribution

Outcomes are generally aggressive with poorer survival — worse than B-cell lymphoma and Hodgkin lymphoma, with some exceptions. Contributing factors: these are rare so there is limited clinical trial data, there may be intrinsic drug resistance, and patients typically have advanced stage disease at diagnosis.

Phenotype

T-cell maturation and the precursor/peripheral divide

Receptors are either alpha-beta or gamma-delta. Additional general features of T-cell neoplasms: geographical incidence variation with increased frequency in Asia, racial predisposition, HTLV-1-related lymphomas, and cytokine-related symptoms at diagnosis — notably hypercalcemia via osteoclast activating factor and hemophagocytic syndrome.

Classification

Why T-cell lymphomas are grouped by clinical presentation

B-cell lymphomas are classified according to stage of development. T-cell lymphomas are classified according to clinical presentation, because the usual classification markers do not work:

• Morphology — some have characteristic appearances, but there is striking variability and extensive morphologic overlap
• Immunophenotype — there is no clear surface marker of clonality (no T-cell equivalent of light chain restriction), and usually no disease-specific T-cell marker phenotypes
• Molecular genetics — T-cell receptor gene rearrangement establishes clonality; t(2;5) is associated with anaplastic large cell lymphoma

MF

Mycosis fungoides

• Adults, male:female 2:1; the most common cutaneous T-cell lymphoma; may show dermatopathic lymphadenopathy
• Cell of origin: mature CD4-positive epidermotropic T cell
• Progression of lesions: initially non-specific scaly eruptions, then isolated patches usually beginning on the trunk with variable stability over months to years, progressing to generalized plaques which may become erythroderma, then to tumors; extracutaneous spread in end-stage disease
• Morphology: small to medium T cells with cerebriform nuclei; epidermotropic infiltrates, generally single-cell; Pautrier microabscesses are highly characteristic but present in a minority of cases
• Immunophenotype: positive for CD2, CD3, CD5, CD4, and CLA (cutaneous lymphocyte antigen); negative for CD7, CD8, and ALK
• Genetics: clonal T-cell receptor gene rearrangement; complex karyotypes especially with advanced disease, with no specific changes
• Indolent course but incurable. Limited disease has an excellent outlook with little decrease in life expectancy; extensive disease is poor. Worse prognosis: age >60, increased LDH, large T-cell transformation

Sézary

Sézary syndrome

• Rare systemic adult disease, over 60 years of age, male predominance
• Also pruritus, alopecia, palmar/plantar hyperkeratosis; a subset is associated with UV radiation
• Morphology: medium T cells with cerebriform nuclei; skin changes similar to mycosis fungoides; lymph nodes show ± dermatopathic changes
• Blood involvement: classical Sézary cells are large, and more than 1000 per mL of blood are required
• Bone marrow is remarkably spared — involvement is sparse and usually interstitial
• Immunophenotype: positive for CD2, CD3, CD5, CD4, CLA, and the skin homing receptor CCR4; negative for CD7, CD8, ALK. Aberrant phenotypes are common, with an increased CD4/CD8 blood ratio >10:1 and increased CD4+ CD7− T cells
• Genetics: clonal T-cell beta receptor gene rearrangement; complex karyotypes common with no specific changes

ATLL

Adult T-cell leukemia/lymphoma

• Adults, median 47 years, male:female 1.5:1; widely disseminated disease
• Human T-cell leukemia virus 1 (HTLV-1) — long latency after infection very early in life; transmitted by breast milk, sexual intercourse, or blood products. HTLV-1 alone is not sufficient; additional genetic hits are needed
• Endemic in Japan, the Caribbean, and Central Africa; sporadic in the USA
• Cell of origin: CD4-positive peripheral regulatory T cell
• Morphology: pleomorphic lymphocytes with a high nuclear:cytoplasmic ratio; “flower cells” with polylobated nuclei. Lymph node and spleen involvement; blood and marrow involvement with a leukemic phase common, usually greater than the degree of marrow involvement. Extranodal disease in 50%, especially skin, where Pautrier-like microabscesses occur, plus lung, liver, GI tract, and CNS
• Immunophenotype: positive CD2, CD3, CD5, CD4, CD25; negative CD7, CD8, ALK
• Genetics: clonal T-cell receptor gene rearrangement and clonal HTLV-1 integration
• Prognosis: incurable, variable by clinical variant, survival 2 weeks to years. Causes of death include Pneumocystis, cryptococcal meningitis, disseminated herpes zoster, and hypercalcemia

ALCL

ALK-positive anaplastic large cell lymphoma

• 3% of all non-Hodgkin lymphoma, but 10–30% of childhood lymphomas; first three decades, male:female 3:1
• Involves lymph nodes and extranodal sites — skin, soft tissue, lung, liver; bone marrow involvement can be subtle
• Advanced disease in 70% with peripheral and abdominal lymphadenopathy; patients have B symptoms
• 5-year survival 80–90%
• Morphology: large, irregular, bizarre cells spanning a broad spectrum. Hallmark cells are characteristic — large cells with eccentric horseshoe- or kidney-shaped nuclei and a prominent paranuclear eosinophilic Golgi region. Multinucleated wreath cells also occur
• Immunophenotype: strongly and uniformly CD30-positive in a membranous and Golgi pattern. ALK-positive, and the staining pattern correlates with the underlying genetic abnormality — cytoplasmic and nuclear staining indicates t(2;5). ALCL may be of T-cell or null lineage, and most tumors are CD3-negative, CD5-negative, or T-cell receptor negative. Positive for cytotoxic granule proteins TIA-1, granzyme B, and perforin; EBV-negative and B-cell antigen negative
• Genetics: 75–80% carry t(2;5)(p23;q35) — the nucleophosmin (NPM) gene at 5q35 joined to the ALK gene at 2p23, producing the NPM-ALK fusion protein. Variant partners in about 25% include TPM3, TFG, ATIC, MSN, CLTC, TPM4, RNF213, and MYH9

NK/T

Extranodal NK/T-cell lymphoma, nasal type

• Epstein-Barr virus is involved in pathogenesis
• Involves the upper aerodigestive tract; extranasal cases most commonly involve skin; bone marrow involved in 10–15%
• Necrosis with vascular destruction — the tumor is angiodestructive
• Asians and indigenous populations of Mexico, Central and South America; adults 35–58 years, male predilection
• Morphology: variable cell size; cells may contain azurophilic granules; ulcerated mucosal surfaces; pseudoepitheliomatous hyperplasia
• Immunophenotype: NK-cell lineage in 66–75% — CD2, cytoplasmic CD3, CD56, plus cytotoxic markers TIA-1, granzyme B, perforin. T-cell lineage in 25–33% — CD2, CD3-ε, CD5, CD8, TCR-β, and cytotoxic markers. EBV-positive; clonal T-cell receptor rearrangement only in the T-cell lineage cases
• Prognosis is poor; extranasal tumors have a poorer prognosis. Adverse factors: elevated CRP, anemia, thrombocytopenia, and a high proliferation rate

Highest yield

Carry-out points

1. TdT separates precursor from peripheral — TdT-positive lymphoblasts are the acute lymphoblastic diseases; TdT-negative mature T cells are the peripheral T-cell lymphomas.
2. T-cell lymphomas are classified by clinical presentation — cutaneous, leukemic/disseminated, extranodal, nodal — because morphology overlaps, there is no surface marker of clonality, and phenotypes are rarely disease-specific.
3. Clonality requires T-cell receptor gene rearrangement, and a clonal T-cell population is not necessarily neoplastic.
4. T-cell lymphomas are generally more aggressive than B-cell and Hodgkin lymphoma; ALK-positive ALCL is the notable favorable exception.
5. Two viruses drive specific entities: HTLV-1 → ATLL and EBV → extranodal NK/T-cell lymphoma.
6. Cytokine-mediated systemic effects are characteristic — hypercalcemia from osteoclast activating factor and hemophagocytic syndrome.

Overview

What sets Hodgkin lymphoma apart

• 0.7% of all new cancers in the United States, about 8,000 new cases each year
• Average age 32 — one of the most common lymphomas of young adults
• The first cancer to be successfully treated with radiation and chemotherapy; curable in most cases
• Presents as painless lymphadenopathy, with B symptoms — fever, night sweats, weight loss

Morphology

The defining morphologic feature

Rare neoplastic cells — Reed-Sternberg cells — in an abundant inflammatory background of lymphocytes, macrophages, and granulocytes, which constitute 90% of the tumor cellularity.

Pathogenesis: in the majority of cases the Ig genes of RS cells have undergone both V(D)J recombination and somatic hypermutation, establishing an origin from germinal center or post-germinal center B cells. The mechanism involves activation of the transcription factor NF-κB, by several routes including EBV infection. The transformed B cells then secrete cytokines, chemokines and other factors that attract inflammatory cells.

Classification

Subtypes and immunophenotype

Separately classified: Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL).

Reed-Sternberg cells and variants include the classic binucleate form, mononuclear, lacunar, and mummified cells.

NLPHL

Nodular lymphocyte-predominant Hodgkin lymphoma

• Uncommon
• Typically a young male with cervical or axillary lymphadenopathy
• Frequent L&H (“popcorn”) cell variants in a background of follicular dendritic cells and reactive B cells; identification of LP cells is crucial for diagnosis
• Phenotype: PAX5-positive, CD20-positive, OCT2-positive; CD30-negative, CD15-negative
• May evolve to T-cell/histiocyte-rich large B-cell lymphoma (diffuse)

Prognosis

Clinical features and outcome

• Painless lymphadenopathy is the presentation
• Nodular sclerosis and lymphocyte predominance usually present at clinical stage I–II and are free of systemic symptoms
• Patients with disseminated disease (stage III–IV), and the mixed cellularity and lymphocyte-depleted types, are more likely to present with B symptoms — fever, night sweats, weight loss
• With current treatment protocols, tumor stage rather than histologic type is the important prognostic variable
• Cure rate for stage I and stage IIA is 90%; even in advanced disease (stage IVA or IVB), 60–70% five-year disease-free survival is common
• Long-term survivors treated with alkylating chemotherapy and radiotherapy have an increased risk of developing a secondary malignancy

Highest yield

Carry-out points

1. Hodgkin lymphoma is defined by Reed-Sternberg cells, which are rare cells in an abundant inflammatory background making up 90% of the cellularity.
2. It arises in a single node or chain and spreads to anatomically contiguous lymphoid tissue, unlike the generalized adenopathy of non-Hodgkin lymphoma.
3. RS cells are of germinal center or post-germinal center B-cell origin, surviving through NF-κB activation, which also drives the cytokine secretion that recruits the inflammatory background.
4. Classical HL: PAX5+, CD30+, CD15+, CD20−. NLPHL: PAX5+, CD20+, OCT2+, CD30−, CD15−, with popcorn (L&H) cells.
5. Nodular sclerosis is 70% of cases; nodular sclerosis and lymphocyte predominance usually present at low stage without B symptoms, while mixed cellularity and lymphocyte-depleted more often have B symptoms and advanced stage.
6. Stage rather than histologic subtype drives prognosis; 90% cure in stage I–IIA, and 60–70% five-year disease-free survival even in stage IV.
7. Long-term survivors carry an increased risk of secondary malignancy from alkylating chemotherapy and radiotherapy.

Origin

The mononuclear phagocyte system

A specialized group of cells of the innate immune system.

Definition

What LCH is, and how it is recognized

• A clonal neoplastic process of Langerhans-type cells — LCH cells are S100+, CD1a+, Langerin+
• Incidence estimated at 4–5 per million per year in childhood and 1–2 per million per year in adults
• LCH cells are large with grooved and folded nuclei and abundant pink, finely granular cytoplasm
• Birbeck granules — racket-shaped pentalaminar structures identifiable only on electron microscopy, containing langerin

Molecular genetics: BRAF p.V600E, an activating valine-to-glutamate mutation at residue 600, in 55–60% of cases, and detectable by immunohistochemical stain. Less frequent mutations include TP53, RAS, and MET.

Spectrum

The clinical spectrum of LCH

Highest yield

Carry-out points

1. Langerhans cells are dendritic cells of the innate immune system and derive from myeloid stem cells.
2. BRAF p.V600E is the most frequent genetic abnormality in LCH, present in 55–60% and detectable by immunohistochemistry.
3. LCH is composed of large histiocytoid cells with grooved nuclei and abundant pink cytoplasm expressing S100, CD1a, and langerin (CD207).
4. Birbeck granules are pathognomonic racket-shaped structures identifiable only by electron microscopy.
5. Prognosis is worst in multifocal multisystem LCH (Letterer-Siwe) and indolent in unifocal/multifocal unisystem LCH (eosinophilic granuloma) and in pulmonary LCH, which is smoking-associated and regresses on cessation.

Anatomy

Normal spleen — two compartments, two jobs

A lymphoid organ in the upper left quadrant, covered by a thin capsule. The cut surface is deep red (red pulp) with Malpighian corpuscles (white pulp). It is divided into morphologic compartments with different functions — filtration and immunity.

Function

Four splenic functions

1. Antibody production
2. Phagocytosis of blood cells and particulate matter — including defense against encapsulated bacteria
3. Hematopoiesis — during fetal development, and extramedullary hematopoiesis later in life in chronic anemia and myeloid disorders
4. Sequestration of blood elements — normally one third of the platelet mass is in the spleen; with splenomegaly, 80–90% of platelets may be sequestered

Splenomegaly

Enlargement and congestion

Increased splenic weight — normal is 150 g — which may result in hypersplenism.

Congestive splenomegaly results from obstruction of venous outflow producing red pulp congestion. Causes are cirrhosis of the liver, portal or splenic vein thrombosis, and cardiac failure. Morphology: the red pulp is expanded and beefy red with loss of white pulp, and fibrosis of vessels and sinusoids when long-standing.

Rupture

Splenic rupture and infarction

Neoplasms

Tumors involving the spleen

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Carry-out points

1. The spleen is composed of red pulp (filtration) and white pulp (immunity), with PALS holding T cells and follicles holding B cells.
2. Filtration is accomplished through the “open” circulation via the cords of Billroth.
3. Splenomegaly may result in hypersplenism, sequestration of blood elements, and rupture; normal splenic weight is 150 g, and with splenomegaly 80–90% of platelets may be sequestered.
4. Cirrhosis and heart failure are common causes of congestive splenomegaly due to obstructed venous outflow.
5. Splenic infarcts are secondary to vascular occlusion — thromboembolism, sickle cell anemia, and others.
6. Trauma is the most common cause of rupture; spontaneous rupture follows rapid enlargement in mononucleosis, malaria, typhoid, and lymphoid neoplasms.
7. Hematopoietic neoplasms commonly involve the spleen; the primary splenic lymphoma is splenic marginal zone lymphoma.

Normal

Anatomy and function

• Arises from the 3rd branchial pouch
• Critical role in T-cell differentiation and cell-mediated immunity: T cells migrate from the marrow to the thymus, are “educated” to distinguish self from non-self antigens, and mature T cells then migrate to the periphery
• Grows until puberty, then involutes with fatty replacement

Development

Thymic dysplasia, aplasia, and DiGeorge syndrome

• Incomplete (dysplasia) or complete lack of (aplasia) thymic development, associated with some primary immunodeficiencies — small size, no cortical and medullary zones, no Hassall corpuscles
• Aplasia = DiGeorge syndrome; Dysplasia = SCID, ataxia-telangiectasia, incomplete DiGeorge
• Distinguished from acute thymic involution (stress, infection) by the absence of well-formed Hassall corpuscles

DiGeorge syndrome: thymic and parathyroid aplasia or severe hypoplasia, giving markedly decreased T cells; variable defects involving the heart and great vessels; defects in cell-mediated immunity; 22q11 deletion. Thymic cysts are benign incidental findings.

Hyperplasia

True thymic hyperplasia versus thymic follicular hyperplasia

Tumors

Neoplasms of the thymus

Thymoma — a tumor of epithelial thymic cells. Clinical presentation splits three ways:

Patients may also present with other autoimmune disorders or pure red cell aplasia.

Highest yield

Carry-out points

1. The thymus is the site of T-cell development, arising from the 3rd branchial pouch, with a cortex of immature thymocytes, a medulla of maturing T cells, and Hassall corpuscles in the medulla.
2. DiGeorge syndrome is an immunodeficiency associated with thymic hypoplasia/aplasia and a 22q11 deletion, with parathyroid aplasia and cardiac/great vessel defects.
3. Absence of well-formed Hassall corpuscles distinguishes dysplasia/aplasia from acute thymic involution.
4. Thymic follicular hyperplasia has B-cell follicles and is frequently associated with myasthenia gravis (65%) — contrasted with true thymic hyperplasia, which is enlargement with normal microscopy.
5. Thymomas arise from thymic epithelial cells, and approximately 40% of patients with thymoma have myasthenia gravis.
6. Thymic carcinoma is 5% of thymic epithelial neoplasms, is not associated with myasthenia gravis, is usually squamous cell carcinoma, and has an 18 month median survival.

Lecture 07

White blood cells and reactive changes — Randall

The “normal responses” lecture: how marrow and lymph nodes react to demand before anything is neoplastic. Every leukemia question secretly asks “could this be reactive?” — and this is where the answer lives. Two habits govern the whole lecture: work from absolute counts, not percentages, and learn what a stressed but healthy marrow looks like so you can recognize when it is not.

Lecture 08

Acute leukemias — Randall

This lecture hands you the block's most important number: ≥20% blasts = acute. “Acute” does not mean high count or fast onset — it means the clone is stuck at the blast stage. Chronic means <20% with cells that still mature (CLL = mature B cells, CML = maturing myeloid cells). The clinical presentation is simply what blasts crowd out: anemia → fatigue, neutropenia → infection, thrombocytopenia → mucosal bleeding and petechiae.

Lecture 09

Myelodysplastic neoplasms — Randall

The chronic side of the 20% line holds three categories, and they are split first by the blood count: MPN = cytoses, MDS = cytopenias, MDS/MPN overlap = both. This is the MDS half of that mirror — a clonal stem cell disorder whose maturation defects mean the cells die in the marrow before release. That is ineffective hematopoiesis, and it produces the defining paradox: a hypercellular marrow with empty blood. Production is not the problem; surviving to release is.