🧬 Section 503.2 · Vitamin B12 (Cobalamin) Deficiency

Nelson Textbook of Pediatrics 22nd Edition | B12 deficiency causes megaloblastic anemia and neurologic manifestations (subacute combined degeneration). Causes: nutritional (maternal vegan, infant breastfed), pernicious anemia (autoimmune, rare in children), intrinsic factor deficiency, Imerslund-Gräsbeck syndrome (with proteinuria), transcobalamin deficiency, nitrous oxide, fish tapeworm. Diagnosis: ↓B12, ↑MMA (specific), ↑homocysteine. Treatment: IM hydroxocobalamin.

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📋 30 Clinical Scenarios — Vitamin B12 (Cobalamin) Deficiency

📇 High‑Yield Review Cards (Vitamin B12 Deficiency)

🩺 Clinical Recognition: Vitamin B12 Deficiency in Children

Select a presentation for diagnostic clues and management.

📋 Stepwise Management of Vitamin B12 Deficiency

🔑 Key Points — Nelson Section 503.2
• B12 deficiency → ↑methylmalonic acid (MMA) and ↑homocysteine (MMA specific for B12).
• Neurologic manifestations: paresthesias, ataxia, hypotonia, developmental regression, may occur without anemia.
• Pernicious anemia (autoimmune gastritis) is rare in children; anti-IF antibodies diagnostic.
• Imerslund-Gräsbeck syndrome: B12 malabsorption + benign proteinuria.
• Transcobalamin deficiency: normal total B12 (80% bound to haptocorrin) but low holotranscobalamin.
• Treatment: IM hydroxocobalamin (preferred over cyanocobalamin); lifelong for malabsorption syndromes.

    ⚡ Reflex Prompts — Clinical Decisions in B12 Deficiency

    📖 Summary: Vitamin B12 Deficiency — Nelson Section 503.2