A 35-year-old woman from rural India presents with severe anemia (hemoglobin 5.8 g/dL), glossitis, paresthesias, and megaloblastic changes on bone marrow examination. Serum vitamin B12 is 120 pg/mL (normal >200). What is the drug of choice for her condition?

Explanation

## Diagnosis: Vitamin B12 Deficiency Anemia with Neurological Manifestations ### Clinical Presentation The patient presents with: - Severe megaloblastic anemia (Hb 5.8 g/dL) - Glossitis (inflamed tongue) - Paresthesias (neurological involvement) - Megaloblastic bone marrow changes - Low serum B12 (120 pg/mL) **Key Point:** The presence of neurological symptoms (paresthesias) is a critical indicator for parenteral B12 therapy. Oral supplementation is inadequate when neurological damage is present. ### Why Intramuscular Injection? **High-Yield:** Intramuscular cyanocobalamin bypasses the gastrointestinal tract and ensures rapid, reliable absorption. This is essential when: 1. Neurological symptoms are present (risk of irreversible spinal cord damage if delayed) 2. Malabsorption is the underlying cause (pernicious anemia, post-gastrectomy, dietary deficiency) 3. Severe anemia requires rapid correction ### Comparison of B12 Replacement Routes | Route | Absorption | Onset | Indication | Efficacy | |-------|-----------|-------|-----------|----------| | **IM Cyanocobalamin** | 100% (bypasses GI) | Days | Malabsorption, neurological symptoms | Excellent | | Oral Cyanocobalamin | 1–2% (passive) | Weeks–months | Dietary deficiency only, no neurological signs | Poor in malabsorption | | Sublingual/Nasal | Variable | Weeks | Mild deficiency, compliance issues | Unreliable | | IV Cyanocobalamin | 100% | Hours | Emergency, severe anemia | Rapid but rarely needed | **Clinical Pearl:** Oral B12 supplementation is ONLY appropriate for dietary deficiency without neurological manifestations. Once neurological symptoms develop, parenteral therapy is mandatory to prevent permanent neurological damage (subacute combined degeneration of the spinal cord). ### Treatment Protocol ```mermaid flowchart TD A[B12 deficiency confirmed] --> B{Neurological symptoms present?} B -->|Yes| C[IM Cyanocobalamin immediately] B -->|No| D{Malabsorption?} D -->|Yes| E[IM Cyanocobalamin] D -->|No| F[Oral supplementation acceptable] C --> G[1000 µg weekly x 4, then monthly] E --> G ``` **Mnemonic:** **PERNICIOUS** = Parenteral (IM) therapy for neurological symptoms in B12 deficiency. **Warning:** Delaying parenteral therapy in the presence of paresthesias risks irreversible spinal cord demyelination (subacute combined degeneration). Oral therapy is inadequate and dangerous in this context.