A 42-year-old male construction worker from rural Maharashtra presents with a 3-month history of progressive numbness and tingling in both feet, difficulty walking, and recent onset of confusion. On examination, he has diminished vibration and proprioception sense in lower limbs, and mild ataxia. His diet consists mainly of polished rice and dal with minimal vegetables or meat. Blood glucose is 98 mg/dL, and serum B12 is 450 pg/mL (normal). MRI brain is unremarkable. Which vitamin deficiency is most likely responsible for his neurological syndrome?

Explanation

## Clinical Presentation Analysis **Key Point:** This patient presents with a classic triad of thiamine deficiency: peripheral neuropathy (paresthesias, sensory loss), ataxia (gait disturbance), and encephalopathy (confusion). The normal B12 level rules out cobalamin deficiency. ## Thiamine (B1) Deficiency Pathophysiology Thiamine (pyrophosphate) is an essential cofactor for: 1. Transketolase (pentose phosphate pathway) 2. Pyruvate dehydrogenase (glucose metabolism) 3. α-ketoglutarate dehydrogenase (TCA cycle) 4. Branched-chain amino acid metabolism Deficiency impairs energy metabolism in high-demand tissues (CNS, PNS), leading to: - **Dry beriberi:** peripheral neuropathy, cardiac involvement - **Wet beriberi:** high-output cardiac failure, pulmonary edema - **Wernicke-Korsakoff syndrome:** ophthalmoplegia, ataxia, confusion, memory loss ## Risk Factors in This Case **High-Yield:** Polished rice diet is a major risk factor in India and Southeast Asia. Milling removes the thiamine-rich bran layer. Combined with minimal protein intake (limited meat/vegetables), this creates a perfect storm for deficiency. ## Differential Diagnosis Table | Vitamin | Neurological Features | Key Distinguishing Factor | |---------|----------------------|---------------------------| | **Thiamine (B1)** | Peripheral neuropathy + ataxia + encephalopathy | Normal B12; diet of polished rice | | Cobalamin (B12) | Subacute combined degeneration (posterior/lateral columns) | B12 level normal (450 pg/mL) | | Niacin (B3) | Dermatitis, diarrhea, dementia (4 Ds) | No dermatitis; no GI symptoms | | Pyridoxine (B6) | Peripheral neuropathy (sensory predominant) | Less likely with normal B12 | **Clinical Pearl:** The presence of ataxia (cerebellar dysfunction) + peripheral neuropathy + encephalopathy in a malnourished patient with a thiamine-poor diet is pathognomonic for thiamine deficiency. ## Diagnosis and Management **Mnemonic:** **WERNICK** — Wernicke encephalopathy features: - **W**obbliness (ataxia) - **E**ye signs (ophthalmoplegia) - **R**ecent confusion - **N**ystagmus - **I**ncontinence - **C**onfabulation - **K**orsakoff (memory loss) This patient has partial Wernicke syndrome (ataxia + confusion). **Treatment:** Thiamine 100 mg IV/IM daily for 3–5 days, then oral 10 mg daily. Early replacement can prevent progression to irreversible Korsakoff syndrome.