Paroxysmal nocturnal hemoglobinuria for neet pg 2026. Include all topics related to Pathology aspect of it that is required for an neet pg.
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Searching across multiple pathology aspects of PNH simultaneously.
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paroxysmal nocturnal hemoglobinuria pathogenesis PIG-A mutation GPI anchor complement
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 3043
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paroxysmal nocturnal hemoglobinuria clinical features diagnosis hemolysis thrombosis flow cytometry
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 3022
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PNH CD55 CD59 DAF MIRL complement regulatory proteins intravascular hemolysis
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PNH aplastic anemia bone marrow failure thrombosis Budd-Chiari Ham test sucrose lysis
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Paroxysmal Nocturnal Hemoglobinuria (PNH) — NEET PG 2026 | Pathology
1. DEFINITION & OVERVIEW
PNH is an acquired clonal disorder of hematopoietic stem cells characterized by:
- Intravascular hemolytic anemia
- Pancytopenia
- Venous thrombosis
"PNH is a truly unique clinical condition" — Harrison's 21st ed. (p. 3022)
2. ETIOLOGY & PATHOGENESIS
Somatic Mutation — The Root Cause
| Feature | Detail |
|---|---|
| Gene mutated | PIG-A gene (Phosphatidylinositol Glycan class A) |
| Type of mutation | Somatic (acquired), X-linked gene |
| Cell of origin | Multipotent hematopoietic stem cell |
| Inheritance | NOT inherited — acquired somatic mutation |
GPI Anchor — The Core Mechanism
- The PIG-A gene encodes an enzyme essential for biosynthesis of the glycosylphosphatidylinositol (GPI) anchor
- GPI anchors attach specific protective proteins to the cell surface membrane
- Mutation → deficiency/absence of GPI-anchored proteins on all progeny cells (RBCs, WBCs, platelets)
Key GPI-Anchored Proteins Lost in PNH
| Protein | Full Name | Function | Consequence of Loss |
|---|---|---|---|
| CD55 | Decay Accelerating Factor (DAF) | Degrades C3/C5 convertases | Uncontrolled complement activation |
| CD59 | Membrane Inhibitor of Reactive Lysis (MIRL) / Protectin | Blocks C5b–9 (MAC) assembly | Lysis of RBCs by MAC |
| CD14 | — | Monocyte marker | — |
| CD16 | FcγRIII | NK cell marker | — |
| Urokinase receptor (uPAR) | CD87 | Plasminogen activation | Contributes to thrombosis |
High-yield: CD59 is the most important — its absence is primarily responsible for hemolysis. CD55 is also critical.
Why Hemolysis is Intravascular
- Absent CD55 & CD59 → complement cascade proceeds unchecked via alternative pathway
- Terminal complement complex (MAC = C5b-6-7-8-9) directly lyses RBCs in the bloodstream
- Result: intravascular hemolysis → hemoglobinuria (classic morning dark urine)
3. THREE CELL POPULATIONS (PNH Types)
| Type | CD55/CD59 | Sensitivity to Complement |
|---|---|---|
| Type I | Normal expression | Normal sensitivity |
| Type II | Partial deficiency | Moderately sensitive (3–5× normal) |
| Type III | Complete absence | Highly sensitive (15–25× normal) |
Type III cells are responsible for most clinical hemolysis.
4. WHY THE CLONE EXPANDS (Clonal Selection)
- PIG-A mutations are actually common in normal individuals but the clones don't expand
- In PNH, there is often a background of immune-mediated bone marrow failure (aplastic anemia)
- The GPI-deficient cells escape T-cell mediated autoimmune destruction (which targets GPI-anchored antigens) → selective survival advantage
- This explains the strong link between PNH and aplastic anemia
5. CLINICAL FEATURES (Pathology-relevant)
The Classic Triad
- Intravascular hemolytic anemia
- Pancytopenia (bone marrow failure component)
- Venous thrombosis
Hemolysis Details
- Nocturnal hemolysis (sleep → mild respiratory acidosis → complement activation)
- Morning hemoglobinuria — dark red/brown urine on waking (classic but present in minority)
- Ongoing chronic intravascular hemolysis even without overt hemoglobinuria
- Elevated LDH, low haptoglobin, hemosiderinuria
Thrombosis — High-Yield Mechanism
- Most common cause of death in PNH
- Sites: Hepatic veins (Budd-Chiari syndrome) ← most classic, portal veins, cerebral veins, mesenteric veins
- Mechanism: GPI-deficient platelets + complement-activated platelet aggregation + loss of uPAR → thrombotic tendency
Bone Marrow
- Hypoplastic marrow (aplastic anemia picture) with PNH clone superimposed
- PNH ↔ Aplastic anemia: close pathological relationship
6. LABORATORY DIAGNOSIS
Screening Tests (Classical — Older)
| Test | Principle | Result in PNH |
|---|---|---|
| Ham's Test (Acidified Serum Test) | Acidified serum activates complement via alternative pathway | Positive (hemolysis) |
| Sucrose Lysis Test (Sugar Water Test) | Low ionic strength activates complement | Positive (more sensitive, less specific) |
Ham's test = gold standard (classic/historical); more specific than sucrose lysis test.
Confirmatory Test (Current Gold Standard)
| Test | Details |
|---|---|
| Flow Cytometry | Detects absence of CD55 & CD59 on RBCs and granulocytes |
| FLAER (Fluorescent Aerolysin) | Binds directly to GPI anchor; most sensitive; uses granulocytes |
Flow cytometry is the current gold standard for PNH diagnosis. FLAER is the most sensitive method.
Other Lab Findings
| Finding | Significance |
|---|---|
| Elevated LDH | Intravascular hemolysis marker |
| Hemosiderinuria | Chronic hemolysis (iron in urine) |
| Low serum haptoglobin | Free Hb scavenging |
| Hemoglobinuria | Classic; not always present |
| Coombs test | Negative (DAT negative) — key differentiator |
| Pancytopenia | Bone marrow failure |
| Elevated reticulocyte count | Compensatory |
| Low serum iron (chronic) | Urinary iron loss |
7. PATHOLOGICAL CLASSIFICATION (PNH Variants)
| Type | Features |
|---|---|
| Classic PNH | Hemolysis dominant, no marrow failure |
| PNH with aplastic anemia | Combined; most common presentation |
| Subclinical PNH | Small clone detected, no symptoms |
8. COMPLICATIONS
| Complication | Mechanism |
|---|---|
| Budd-Chiari syndrome | Hepatic vein thrombosis — most classic site |
| Renal failure | Hemoglobin nephrotoxicity, renal vessel thrombosis |
| Pulmonary hypertension | Free Hb scavenges NO → vasoconstriction |
| Esophageal spasm / dysphagia | NO depletion |
| Transformation to AML/MDS | Rare (~1–2%) |
| Aplastic anemia | Bone marrow failure progression |
9. TREATMENT (for conceptual pathology context)
| Drug | Mechanism | Notes |
|---|---|---|
| Eculizumab | Anti-C5 monoclonal antibody → blocks MAC formation | Drug of choice; humanized monoclonal Ab |
| Ravulizumab | Long-acting anti-C5 Ab | Newer agent |
| Allogeneic HSCT | Curative | Only cure |
| Anticoagulation | Thrombosis prevention/treatment | — |
| Iron/folate supplementation | Urinary losses | — |
Eculizumab predisposes to Neisseria meningitidis infections → meningococcal vaccination mandatory before starting.
10. HIGH-YIELD ONE-LINERS FOR NEET PG
- Gene: PIG-A mutation → somatic, X-linked
- Mechanism: Loss of GPI anchor → loss of CD55 (DAF) & CD59 (MIRL)
- Most important protein lost: CD59 (MIRL/Protectin)
- Type of hemolysis: Intravascular (Coombs NEGATIVE)
- Classic test: Ham's acidified serum test (positive)
- Gold standard now: Flow cytometry (CD55/CD59 on RBCs and granulocytes)
- Most sensitive test: FLAER
- Most common cause of death: Thrombosis (especially Budd-Chiari)
- Drug of choice: Eculizumab (anti-C5)
- Only cure: Allogeneic HSCT
- Relationship: PNH ↔ Aplastic anemia (bidirectional)
- Urine finding: Hemoglobinuria (morning), Hemosiderinuria (chronic)
- Pathways activated: Alternative complement pathway → MAC → lysis
11. COMPARISON: PNH vs Other Hemolytic Anemias
| Feature | PNH | Hereditary Spherocytosis | AIHA |
|---|---|---|---|
| Type | Acquired | Hereditary | Acquired |
| Hemolysis | Intravascular | Extravascular | Extravascular |
| Coombs test | Negative | Negative | Positive |
| Defect | GPI anchor (CD55/59) | Spectrin/Ankyrin | Anti-RBC antibodies |
| Osmotic fragility | Normal | Increased | Normal |
| Thrombosis | Yes (major) | No | No |
12. QUICK MEMORY AID
PNH = PIG-A → No GPI → No CD55/CD59 → Complement runs wild → Intravascular lysis
- Pig-A mutation
- No GPI anchor
- Hemolysis (intravascular) + Hemoglobinuria
"DAF (CD55) decays convertases; MIRL (CD59) stops MAC — lose both, complement has a field day."
This covers the complete pathology of PNH as required for NEET PG 2026 — mechanism, classification, lab diagnosis, complications, and treatment rationale. Focus especially on the GPI anchor pathway, CD55/CD59, Ham's test vs flow cytometry, intravascular hemolysis with negative Coombs, and thrombosis as the major complication.
I want you to convert the basic knowledge of paroxysmal nocturnal hemoglobinuria that you mentioned about in the pathology aspect and also the highlighted points which you mentioned and all the important points required for complete pathology and understanding of this topic. I want you to prepare anki cards based on this to be put into Anki droid app. And the questions and the cards should also help me to answer an actual clinical MCQ. Restrict the cards to pathology aspect, but it should also be able to help me answer clinical MCQ. Not just give me factual information. Ultimate aim is to answer clinical MCQs in PGE 2026 because the pattern has changed from factual to clinical reasoning to clinical reasoning. And don't make new mistakes and don't repeat cards, that is cards with same information, and make each card independent. That is, the front side when I read, when I read in the end for revision, it should be able to understand that the question is from paroxysmal nocturnal hemoglobinuria. So each card should be independent. Don't put it as a continuation. I want it in the format front side, and then when I press the short answer button, the back side should come in that format.
Perfect. Below is a ready-to-use Anki set in exactly the format you asked:
- Front side (independent, PNH clearly mentioned)
- Back side (short answer style, MCQ-oriented reasoning)
- No continuation dependency
- No duplicate cards
- Focused on Pathology, but framed for clinical MCQ solving
You can copy this into a
.txt file and import into AnkiDroid as tab-separated fields.PNH pathology: A 26-year-old with recurrent dark morning urine, Coombs-negative hemolytic anemia, and hepatic vein thrombosis. What is the single unifying diagnosis? Paroxysmal nocturnal hemoglobinuria (PNH). Classic triad clue: intravascular hemolysis + cytopenia tendency + unusual venous thrombosis (especially Budd-Chiari).
PNH pathology: What is the primary molecular defect in PNH? Acquired somatic mutation in PIGA gene in a hematopoietic stem cell causing defective GPI-anchor synthesis.
PNH pathology: Why is PNH an acquired clonal stem cell disorder and not inherited hemolytic anemia? Mutation is somatic (post-zygotic) in hematopoietic stem cells, so all descendant blood lineages can be affected; no germline inheritance pattern.
PNH pathology: Which membrane anchor is deficient in PNH and why is it high yield? GPI anchor (glycosylphosphatidylinositol) is deficient, so multiple protective surface proteins cannot attach to blood cells.
PNH pathology: Which 2 GPI-linked complement regulatory proteins are most important in PNH MCQs? CD55 (DAF) and CD59 (MIRL/protectin).
PNH pathology: In PNH, loss of CD55 causes what complement abnormality? Failure to accelerate decay of C3/C5 convertases, so complement amplification increases.
PNH pathology: In PNH, loss of CD59 causes what final hemolytic event? Failure to block membrane attack complex formation (C5b-9), causing intravascular RBC lysis.
PNH pathology: Which missing protein is most directly linked to severe intravascular hemolysis in PNH: CD55 or CD59? CD59 loss is most directly linked to terminal complement-mediated lysis severity.
PNH pathology: Why is hemolysis in PNH predominantly intravascular (not extravascular)? Uncontrolled complement activation forms MAC on RBC membrane, lysing RBCs within circulation.
PNH pathology: Coombs test pattern in PNH and diagnostic significance? Direct Coombs (DAT) negative, helping distinguish PNH from autoimmune hemolytic anemia.
PNH pathology: A hemolytic anemia with elevated LDH, low haptoglobin, and hemoglobinuria but DAT negative suggests what pathology mechanism? Complement-mediated intravascular hemolysis of PNH (especially if thrombosis/cytopenia coexist).
PNH pathology: Why is “nocturnal” classically associated with hemoglobinuria in PNH? Mild nighttime respiratory acidosis may increase complement activity, making morning hemoglobinuria more evident (though not always present).
PNH pathology: Is absence of visible hemoglobinuria enough to exclude PNH in modern clinical practice? No. Many cases have chronic hemolysis without dramatic morning urine; diagnose with flow cytometry/FLAER.
PNH pathology: What is the current diagnostic gold standard test for PNH? Flow cytometry demonstrating deficiency of GPI-linked proteins (especially CD55/CD59) on blood cells.
PNH pathology: Why is granulocyte/monocyte flow analysis often preferred over RBC-only analysis in treated patients? RBC populations may be altered by hemolysis/transfusion; granulocyte clone size better reflects true PNH clone.
PNH pathology: What is FLAER in PNH diagnosis and why is it useful? Fluorescent aerolysin binds directly to GPI anchor; highly sensitive for detecting GPI-deficient clones (especially on granulocytes/monocytes).
PNH pathology: Old screening tests in PNH and current exam relevance? Ham test (acidified serum) and sucrose lysis test are historical/classic; flow cytometry is modern standard.
PNH pathology: Ham test in PNH is based on what principle? Acidified serum enhances complement-mediated lysis of GPI-deficient RBCs.
PNH pathology: Sucrose lysis test in PNH is based on what principle? Low ionic strength promotes complement binding and lysis of susceptible PNH RBCs.
PNH pathology: What does a PNH “clone size” mean in flow cytometry reports? Proportion of blood cells lacking GPI-linked proteins; larger clone often correlates with more hemolysis/thrombosis risk.
PNH pathology: Explain Type I, II, III PNH red cells in one line each. Type I: normal CD55/CD59; Type II: partial deficiency; Type III: complete deficiency with highest complement sensitivity.
PNH pathology: Which PNH RBC population is most complement-sensitive and clinically severe? Type III cells (complete CD55/CD59 deficiency).
PNH pathology: Why is thrombosis the deadliest complication in PNH? It is a major cause of mortality due to atypical-site venous thrombosis (hepatic, portal, mesenteric, cerebral veins).
PNH pathology: Most classic venous thrombosis site tested in PNH MCQs? Hepatic vein thrombosis (Budd-Chiari syndrome).
PNH pathology: Clinical vignette clue for PNH thrombosis pattern? Young patient with unexplained abdominal pain/hepatomegaly/ascites due to Budd-Chiari plus hemolysis/cytopenia features.
PNH pathology: Pathology basis of thrombophilia in PNH (exam-oriented)? Complement-mediated platelet activation, procoagulant microparticles, NO depletion from free Hb, impaired fibrinolytic balance.
PNH pathology: How does free plasma hemoglobin contribute to symptoms beyond anemia in PNH? Scavenges nitric oxide causing smooth muscle dystonia: abdominal pain, dysphagia, erectile dysfunction, pulmonary hypertension tendency.
PNH pathology: Why can iron deficiency occur in chronic PNH despite hemolysis? Chronic urinary iron loss from hemoglobinuria/hemosiderinuria.
PNH pathology: Typical urine pathology finding in chronic intravascular hemolysis of PNH? Hemosiderinuria (renal tubular iron handling of filtered hemoglobin).
PNH pathology: Bone marrow relationship between aplastic anemia and PNH that is frequently tested? Strong overlap: aplastic anemia can evolve to PNH; small PNH clones are common in marrow-failure states.
PNH pathology: What explains clonal expansion of PIGA-mutant cells in many PNH patients with marrow failure? Immune selection advantage in aplastic marrow environment favors survival/expansion of GPI-deficient clone.
PNH pathology: Classify PNH into clinically useful categories for exams. Classic hemolytic PNH; PNH with bone marrow failure (AA/MDS overlap); subclinical PNH clone.
PNH pathology: Aplastic marrow + small GPI-deficient clone but no hemolysis is called what? Subclinical/AA-associated PNH clone, not classic symptomatic hemolytic PNH.
PNH pathology: Which transformation risk exists in long-standing PNH/overlap syndromes? Can evolve to MDS/AML (uncommon but important).
PNH pathology: Differentiate PNH from warm AIHA in one high-yield contrast. PNH: DAT negative, complement-regulatory protein deficiency; AIHA: DAT positive, antibody-mediated RBC destruction.
PNH pathology: Differentiate PNH from hereditary spherocytosis in one high-yield contrast. PNH: acquired GPI-defect with thrombosis risk; HS: inherited membrane cytoskeletal defect with spherocytes and splenic extravascular hemolysis.
PNH pathology: If a stem-cell disorder affects RBC, WBC, and platelets by one mutation, what pathology concept should you think of in PNH? Clonal hematopoiesis from mutated multipotent hematopoietic stem cell.
PNH pathology: Why can leukopenia and thrombocytopenia coexist with hemolysis in PNH? Because the underlying disease is a stem cell disorder with marrow failure overlap, not isolated RBC pathology.
PNH pathology: Best single test to monitor biological response to anti-C5 therapy in PNH pathology context? Reduction in markers of intravascular hemolysis (especially LDH) and clinical reduction in hemolytic episodes/thrombosis risk.
PNH pathology: Eculizumab target in complement cascade and pathology consequence? Binds C5, prevents C5b-9 MAC formation, reducing intravascular hemolysis.
PNH pathology: Why must meningococcal risk be considered before complement blockade in PNH? Terminal complement inhibition impairs defense against encapsulated Neisseria, especially meningococcus.
PNH pathology: What remains the only potentially curative treatment from disease-biology perspective in PNH? Allogeneic hematopoietic stem cell transplantation.
PNH pathology: Clinical-MCQ approach: triad that should trigger immediate PNH testing by flow cytometry? Coombs-negative intravascular hemolysis + cytopenia/bone marrow failure + unusual venous thrombosis.
PNH pathology: In a patient with Budd-Chiari and pancytopenia, which hidden diagnosis must be ruled out even if hemoglobinuria is absent? PNH, using flow cytometry/FLAER.
PNH pathology: Why is PNH often delayed in diagnosis despite classic textbook description? Not all three features appear together initially; presentations may be thrombosis-only or cytopenia-dominant early on.
PNH pathology: One-line pathogenesis chain for rapid recall in clinical MCQs. PIGA mutation -> defective GPI anchor -> loss of CD55/CD59 -> complement-mediated intravascular hemolysis + thrombosis-prone clonal hematologic disease.
If you want, I can next give you:
- the same deck as CSV (ready import),
- a reduced 25-card rapid-revision version, and
- a 20 clinical vignette-only PNH pathology deck (new exam pattern style).
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