An 18-year-old male presented to the outpatient department with gum bleeding and fever for the past 2 months. General examination showed pallor and the systemic examination was unremarkable. Laboratory examination revealed Hb level – 3 gm/dl, TLC – 1500/microL, platelet count – 15000/microL. Peripheral smear shows macrocytes and the reticulocyte count is 0.5. Bone marrow examination revealed fatty streaks and absent megakaryocytes but no immature cells. What is the likely diagnosis?

Correct Answer: B. Idiopathic acquired aplastic anemia

Aplastic anemia is a pancytopenia characterized by bone marrow failure with hypocellular marrow and absence of immature cells. This 18-year-old presents with the classic triad: severe anemia (Hb 3 gm/dl), leukopenia (TLC 1500/μL), and thrombocytopenia (platelets 15,000/μL). The bone marrow findings are pathognomonic—fatty streaks (hypocellular marrow) with absent megakaryocytes but critically, NO immature cells (blasts). The low reticulocyte count (0.5) indicates inadequate bone marrow response despite severe anemia, confirming marrow failure rather than hemolysis. The clinical presentation with gum bleeding (thrombocytopenia) and fever (leukopenia with infection risk) over 2 months fits the subacute presentation of acquired aplastic anemia. In India, idiopathic aplastic anemia accounts for ~50% of cases; other causes (drugs, radiation, infections like TB, hepatitis) must be excluded by history. The absence of dysplastic changes and immature cells rules out myelodysplasia. Treatment typically involves immunosuppression (ATG + cyclosporine) or stem cell transplantation in eligible candidates.

Why the other options are wrong

A. Myelodysplastic syndrome — MDS presents with dysplastic changes in cell lines (abnormal morphology, nuclear irregularities, abnormal granulation) and increased blasts (≥5% in marrow). This patient's bone marrow shows NO immature cells and NO dysplasia—only fatty streaks. MDS typically occurs in older adults (>60 years); an 18-year-old with pure hypocellularity without dysplasia is aplastic anemia, not MDS. NBE may trap students who see 'pancytopenia + abnormal marrow' without carefully reading 'absent immature cells.' C. Paroxysmal nocturnal hemoglobinuria — PNH is a clonal stem cell disorder causing hemolysis via complement-mediated lysis of PIG-A mutant cells. It presents with hemolytic anemia (elevated LDH, low haptoglobin, elevated reticulocyte count), NOT pancytopenia with low reticulocytes. This patient's reticulocyte count is 0.5 (inappropriately low), indicating marrow failure, not hemolysis. PNH may coexist with aplasia but is not the primary diagnosis here. Flow cytometry (CD55/CD59 deficiency) would be negative. D. Tuberculosis — TB can cause pancytopenia via bone marrow infiltration (granulomas) or myelofibrosis, but the marrow would show granulomas, caseating lesions, or fibrosis—NOT fatty streaks with absent megakaryocytes. TB-related anemia is typically normocytic or microcytic (chronic disease/iron deficiency), not macrocytic. Fever and gum bleeding are non-specific; absence of TB-specific marrow findings and clinical context (no respiratory symptoms, no weight loss mentioned) make TB unlikely. This is a classic NBE distractor in Indian exams.

High-Yield Facts

Mnemonics

APLASIA = Pancytopenia + Hypocellular marrow + No blasts A—Anemia (Hb <10), P—Pancytopenia (all three lines), L—Low reticulocytes, A—Absent megakaryocytes, S—Severe marrow hypocellularity, I—Immature cells absent, A—Aplastic anemia. Use when differentiating from MDS (which has blasts/dysplasia). RETIC rule: Reticulocyte <1% = Marrow failure; >2% = Hemolysis Low reticulocyte count despite severe anemia = inadequate marrow response = aplasia or infiltration. High reticulocyte = hemolysis or recovery phase. Quick discriminator in pancytopenia cases.

NBE Trap

NBE pairs 'pancytopenia + abnormal marrow' to lure students toward MDS without carefully reading 'absent immature cells'—a key discriminator. Students may also conflate TB-related pancytopenia (marrow infiltration) with aplastic anemia (marrow failure), missing the marrow morphology difference.

Clinical Pearl

In Indian clinical practice, idiopathic aplastic anemia in young patients is a medical emergency requiring urgent immunosuppressive therapy or transplant evaluation. Gum bleeding and fever are warning signs of severe thrombocytopenia and infection risk; patients need protective isolation and transfusion support while awaiting definitive therapy. Early referral to a tertiary hematology center is critical for survival.

_Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 14 (Hematologic Disorders); Harrison's Principles of Internal Medicine, Ch. 110 (Aplastic Anemia and Other Bone Marrow Failure Syndromes)_