A 38-year-old woman from rural Maharashtra presents with a 6-month history of progressive weakness, numbness in her feet, and difficulty walking. On examination, she has loss of vibration sense and proprioception in the lower limbs, brisk reflexes, and a positive Romberg sign. Her diet consists mainly of polished rice and dal with minimal vegetables or fortified foods. Hemoglobin is 9.2 g/dL. Which vitamin deficiency is most likely responsible for her neurological findings?

Explanation

## Clinical Diagnosis: Vitamin B12 Deficiency ### Key Clinical Features **Key Point:** The combination of subacute combined degeneration (SCD) — loss of vibration and proprioception (dorsal column involvement) PLUS brisk reflexes (pyramidal tract involvement) — is pathognomonic for B12 deficiency. ### Mechanism of Neurological Damage Vitamin B12 is essential for: 1. Myelin formation and maintenance 2. Methylation reactions (via methionine synthase) 3. DNA synthesis Deficiency leads to: - **Dorsal column degeneration** → loss of vibration sense, proprioception, ataxia - **Corticospinal tract degeneration** → brisk reflexes, extensor plantar response - **Peripheral neuropathy** → distal paresthesias ### Epidemiology in India **High-Yield:** B12 deficiency is endemic in India due to: - Predominantly vegetarian diet (B12 only in animal products) - Low intake of fortified foods - Malabsorption (pernicious anemia, post-gastrectomy) - Chronic use of metformin or PPIs ### Differential Diagnosis Table | Vitamin | Key Neurological Features | Associated Signs | |---------|--------------------------|------------------| | **B12** | Dorsal/lateral column signs (vibration, proprioception loss + brisk reflexes) | Macrocytic anemia, glossitis, angular cheilitis | | **B1 (Thiamine)** | Wernicke-Korsakoff (ophthalmoplegia, ataxia, confusion); dry beriberi (peripheral neuropathy) | Cardiomegaly (wet beriberi), lactic acidosis | | **B3 (Niacin)** | Dementia, dermatitis, diarrhea (4 Ds) | Photosensitive dermatitis on sun-exposed areas | | **B6 (Pyridoxine)** | Peripheral neuropathy (sensory > motor) | Seizures, sideroblastic anemia | ### Diagnostic Confirmation **Clinical Pearl:** The Romberg sign (loss of balance with eyes closed) indicates dorsal column dysfunction — highly specific for B12 deficiency in this context. - **Serum B12 level** < 200 pg/mL (diagnostic) - **Methylmalonic acid (MMA)** and **homocysteine** elevated (functional B12 deficiency) - **Macrocytic anemia** (MCV > 100 fL) — present in this case (Hb 9.2) - **Intrinsic factor antibodies** if pernicious anemia suspected ### Management **Key Point:** Early treatment is critical — neurological damage may become irreversible if deficiency persists >12 months. - **Parenteral B12:** Cyanocobalamin 1000 µg IM weekly × 6 weeks, then monthly maintenance - **Dietary counseling:** Include fortified foods, eggs, dairy, or B12 supplementation - **Treat underlying cause:** Screen for pernicious anemia, malabsorption, or medication-induced deficiency ### Why Romberg Sign Matters ~~Romberg sign in B1 deficiency~~ — B1 causes *cerebellar* ataxia (positive Romberg but with nystagmus and dysarthria, not dorsal column signs). **Mnemonic for B12 SCD:** **LEMON** = **L**oss of vibration, **E**xtensor plantar response, **M**acrocytic anemia, **O**ptic neuropathy (rare), **N**eurological triad (dorsal + lateral columns + peripheral nerve).