A 35-year-old Indian man with a 10-year history of chronic hemolytic anemia presents with jaundice, splenomegaly, and pigmented gallstones on ultrasound. He reports recurrent episodes of severe abdominal pain and dark urine, particularly during febrile illnesses. His hemoglobin is 8.5 g/dL, reticulocyte count 15%, and indirect bilirubin is elevated. The osmotic fragility test shows increased fragility of RBCs. Direct antiglobulin test is negative. Peripheral blood smear reveals spherocytes and polychromasia. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Hereditary Spherocytosis (HS) ### Key Clinical Features **Key Point:** Hereditary spherocytosis is a chronic, intrinsic RBC membrane disorder characterized by the classic triad of hemolysis, jaundice, and splenomegaly, often complicated by pigmented gallstones. ### Diagnostic Reasoning | Finding | Interpretation | |---------|----------------| | **Chronic hemolysis (10-year history)** | HS is a lifelong condition with persistent hemolysis, not episodic | | **Pigmented gallstones** | Pathognomonic complication; unconjugated bilirubin from chronic hemolysis precipitates as bilirubin stones | | **Splenomegaly** | Chronic extramedullary erythropoiesis and RBC sequestration/destruction | | **Negative DAT** | Rules out immune-mediated hemolysis; indicates intrinsic RBC defect | | **Increased osmotic fragility** | **Hallmark of HS**: Spherocytes lyse at lower osmotic pressures than normal RBCs | | **Spherocytes on smear** | Loss of biconcave shape → spherical, osmotically fragile cells | | **Elevated reticulocytes (15%)** | Bone marrow compensation for chronic hemolysis | | **Elevated indirect bilirubin** | Unconjugated hyperbilirubinemia from RBC destruction | ### Pathophysiology of Hereditary Spherocytosis ```mermaid flowchart TD A[Mutation in membrane protein genes]:::outcome --> B[Defects in spectrin, ankyrin, band 3, or protein 4.2] B --> C[Loss of RBC membrane stability] C --> D[RBC loses biconcave shape → spherocyte] D --> E[Increased osmotic fragility] E --> F[Splenic sequestration and destruction] F --> G[Chronic hemolysis]:::outcome G --> H[Jaundice + Splenomegaly + Pigmented gallstones] ``` **High-Yield:** HS is caused by mutations affecting the vertical linkage of the RBC membrane (spectrin-ankyrin-band 3 complex). Loss of membrane surface area → spherocyte formation → osmotic fragility. ### Osmotic Fragility Test: The Gold Standard **Key Point:** RBCs are placed in hypotonic solutions of decreasing osmolarity. Normal RBCs lyse at ~0.36% NaCl; spherocytes lyse at higher osmolarity (~0.48% NaCl) because they have less surface area relative to volume. ### Inheritance Pattern - **Autosomal dominant** in ~75% of cases - **Autosomal recessive** in ~25% of cases - **De novo mutations** possible ### Why Not Other Diagnoses? **Clinical Pearl:** The combination of **increased osmotic fragility + spherocytes + negative DAT + chronic hemolysis + pigmented gallstones** is pathognomonic for HS. No other hemolytic anemia has this constellation. ### Complications of HS 1. **Pigmented gallstones** (30–50% by age 40) 2. **Aplastic crisis** (parvovirus B19 infection → transient RBC aplasia) 3. **Megaloblastic crisis** (folate deficiency from chronic hemolysis) 4. **Splenic infarction** (rare) ### Management - **Folic acid supplementation** (chronic hemolysis increases folate demand) - **Splenectomy** (definitive treatment; reduces hemolysis by 50–80%) - **Cholecystectomy** (if gallstones present and symptomatic) - **Vaccinations** (before splenectomy: pneumococcal, meningococcal, H. influenzae)