A 45-year-old woman with suspected megaloblastic anemia (MCV 115 fL, reticulocyte count 0.8%) undergoes bone marrow examination. Which morphological finding on bone marrow aspiration is most specific for confirming megaloblastosis?

Question

Accepted Answer

A. Giant metamyelocytes and giant band forms with nuclear-cytoplasmic asynchrony. ## Bone Marrow Morphology in Megaloblastosis **Key Point:** Giant metamyelocytes and giant band forms with **nuclear-cytoplasmic asynchrony** (immature nucleus with mature cytoplasm) are the pathognomonic hallmarks of megaloblastosis. ### Pathophysiology of Megaloblastic Changes In B12/folate deficiency, impaired DNA synthesis causes: 1. **Delayed nuclear maturation** (DNA synthesis blocked) 2. **Normal cytoplasmic maturation** (RNA/protein synthesis intact) 3. **Result:** Large cells with immature chromatin but mature cytoplasm = **nuclear-cytoplasmic asynchrony** ### Diagnostic Morphology ```mermaid flowchart TD A[Bone Marrow in Megaloblastosis]:::outcome --> B[Nuclear-Cytoplasmic Asynchrony]:::outcome B --> C[Immature nucleus
Dispersed chromatin
Large nucleolus]:::action B --> D[Mature cytoplasm
Hemoglobinization
Cytoplasmic maturity]:::action C --> E[Giant Metamyelocytes
Giant Band Forms
Giant Hypersegmented Neutrophils]:::outcome D --> E E --> F[Pathognomonic for
Megaloblastosis]:::outcome ``` ### Morphological Features Table | Finding | Specificity | Mechanism | Diagnostic Value | |---|---|---|---| | **Giant metamyelocytes** | **Very high** | **Nuclear-cytoplasmic asynchrony** | **Gold standard** | | **Hypersegmented neutrophils (>5 lobes)** | High | Delayed nuclear segmentation | Supportive but not pathognomonic | | **Increased cellularity + erythroid hyperplasia** | Low | Non-specific response to anemia | Seen in any hemolytic/regenerative state | | **Ringed sideroblasts** | High | Mitochondrial iron accumulation | Seen in sideroblastic anemia, not megaloblastosis | | **Auer rods** | Very high | Abnormal myeloid differentiation | Seen in AML, not megaloblastosis | **High-Yield:** **Hypersegmented neutrophils** (>5 nuclear lobes) are common in megaloblastosis but NOT pathognomonic — they can be seen in normal aging, myelodysplasia, and other conditions. **Giant metamyelocytes** are far more specific because they represent the immature precursor stage with marked asynchrony. ### Clinical Pearl The key to recognizing megaloblastosis is looking at **precursor cells (metamyelocytes, myelocytes)** rather than mature neutrophils. Giant metamyelocytes are virtually diagnostic of megaloblastosis and warrant immediate investigation for B12/folate deficiency. [cite:Robbins 10e Ch 14]

Answer

B. Hypersegmented neutrophils (>5 lobes) with normal cytoplasm

Answer

C. Ringed sideroblasts and Auer rods

Answer

D. Increased cellularity with erythroid hyperplasia

A 45-year-old woman with suspected megaloblastic anemia (MCV 115 fL, reticulocyte count 0.8%) undergoes bone marrow examination. Which morphological finding on bone marrow aspiration is most specific for confirming megaloblastosis?

Explanation

Bone Marrow Morphology in Megaloblastosis

Pathophysiology of Megaloblastic Changes

Diagnostic Morphology

Morphological Features Table

Clinical Pearl

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A 45-year-old woman with suspected megaloblastic anemia (MCV 115 fL, reticulocyte count 0.8%) undergoes bone marrow examination. Which morphological finding on bone marrow aspiration is most specific for confirming megaloblastosis?

Explanation

Bone Marrow Morphology in Megaloblastosis

Pathophysiology of Megaloblastic Changes

Diagnostic Morphology

Morphological Features Table

Clinical Pearl

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Join our NEET PG community

Finding	Specificity	Mechanism	Diagnostic Value
Giant metamyelocytes	Very high	Nuclear-cytoplasmic asynchrony	Gold standard
Hypersegmented neutrophils (>5 lobes)	High	Delayed nuclear segmentation	Supportive but not pathognomonic
Increased cellularity + erythroid hyperplasia	Low	Non-specific response to anemia	Seen in any hemolytic/regenerative state
Ringed sideroblasts	High	Mitochondrial iron accumulation	Seen in sideroblastic anemia, not megaloblastosis
Auer rods	Very high	Abnormal myeloid differentiation	Seen in AML, not megaloblastosis