A 52-year-old male patient comes with complaints of abdominal pain, nausea, and vomiting. A peripheral blood smear reveals macrocytes and hypersegmented neutrophils and an endoscopy reveals atrophic gastritis. Which of the following conditions is likely to be seen this patient?

Correct Answer: C. Vitamin B12 deficiency

Vitamin B12 deficiency is the unifying diagnosis here. The clinical triad—atrophic gastritis, macrocytic anemia (macrocytes on smear), and hypersegmented neutrophils—is pathognomonic for B12 deficiency. Atrophic gastritis destroys parietal cells, which produce intrinsic factor (IF) necessary for B12 absorption in the terminal ileum. Without IF, dietary B12 cannot be absorbed, leading to megaloblastic anemia. Hypersegmented neutrophils (≥6 lobes, normally 3–4) reflect impaired DNA synthesis affecting all rapidly dividing cells, not just RBCs. The gastrointestinal symptoms (abdominal pain, nausea, vomiting) result from mucosal atrophy and neurological involvement (B12 is essential for myelin synthesis). In India, pernicious anemia (autoimmune atrophic gastritis causing B12 deficiency) is less common than dietary deficiency in vegetarian populations, but when atrophic gastritis is explicitly mentioned, pernicious anemia must be considered. The macrocytic RBCs and hypersegmented neutrophils together exclude other causes of macrocytosis and confirm megaloblastic anemia secondary to B12 deficiency.

Why the other options are wrong

A. Pyridoxine deficiency — Pyridoxine (B6) deficiency causes microcytic, hypochromic anemia (not macrocytic) and sideroblastic changes. It does not produce hypersegmented neutrophils or cause atrophic gastritis. While B6 is involved in heme synthesis, it does not affect DNA synthesis like B12 and folate do. This is an NBE distractor using a B-vitamin to confuse students. B. Folate deficiency — Folate deficiency does cause macrocytic anemia and hypersegmented neutrophils (both affect DNA synthesis), but it does NOT cause atrophic gastritis. Folate is absorbed throughout the small intestine and is not dependent on intrinsic factor. The presence of atrophic gastritis with parietal cell destruction is the discriminating feature pointing to B12, not folate. Folate deficiency typically presents with glossitis and diarrhea, not the gastric pathology seen here. D. Niacin deficiency — Niacin (B3) deficiency causes pellagra (dermatitis, diarrhea, dementia, death—the 4 Ds), not macrocytic anemia. It does not produce hypersegmented neutrophils or affect RBC morphology. Niacin is involved in NAD synthesis for energy metabolism, not DNA synthesis. This is a straightforward distractor with no overlap in clinical presentation.

High-Yield Facts

Mnemonics

MACROCYTIC ANEMIA CAUSES ABCDEFG: Alcohol, B12 deficiency, Chronic liver disease, Drugs (methotrexate), Endocrine (hypothyroidism), Folate deficiency, Graft-versus-host disease. When atrophic gastritis is present, B12 is the answer. B12 vs FOLATE DEFICIENCY B12 = Gastric + Neuro (atrophic gastritis, neurological signs); Folate = Dietary + Diarrhea (no gastritis, no neurological signs). Atrophic gastritis = B12.

NBE Trap

NBE pairs "atrophic gastritis" with "macrocytic anemia" to test whether students reflexively choose folate (which also causes macrocytosis) without recognizing that atrophic gastritis is specific to B12 deficiency via intrinsic factor loss. The trap is forgetting that folate absorption does not require intrinsic factor.

Clinical Pearl

In Indian clinical practice, when a vegetarian patient presents with macrocytic anemia and neurological symptoms (paresthesias, ataxia), B12 deficiency must be ruled out urgently because neurological damage becomes irreversible if treatment is delayed. Atrophic gastritis on endoscopy is the red flag that shifts the diagnosis from folate to B12.

_Reference: Robbins Ch. 14 (Hematologic Disorders); Harrison Ch. 104 (Megaloblastic Anemias); KD Tripathi Ch. 12 (Vitamins)_