A 35-year-old woman from rural Maharashtra presents with a 6-month history of symmetrical peripheral neuropathy affecting the lower limbs, with stocking-glove distribution of sensory loss. On examination, she has a positive Romberg sign and loss of vibration sense. Her diet is predominantly rice-based with minimal animal protein. Which clinical feature best distinguishes her likely thiamine (vitamin B₁) deficiency from niacin (vitamin B₃) deficiency?

Explanation

## Distinguishing Thiamine vs Niacin Deficiency: Neurological Manifestations ### Clinical Presentation Comparison | Feature | Thiamine (B₁) Deficiency | Niacin (B₃) Deficiency | |---------|--------------------------|------------------------| | **Neuropathy Type** | Predominantly **sensory** (stocking-glove), peripheral | Mixed sensory-motor or primarily CNS | | **Dermatitis Pattern** | Absent or minimal | **Pellagrous dermatitis** in sun-exposed areas (pathognomonic) | | **GI Symptoms** | Anorexia, constipation | **Diarrhea** (prominent; part of "4 Ds") | | **Cognitive Changes** | Wernicke-Korsakoff syndrome (memory, confusion) | Dementia, delirium (part of "4 Ds") | | **Motor Involvement** | Preserved early; later foot drop, wrist drop | Often more prominent | **Key Point:** Thiamine deficiency classically presents with a **pure sensory peripheral neuropathy** with preserved motor function in early stages, whereas niacin deficiency causes a mixed picture with prominent dermatitis, diarrhea, and CNS symptoms (the "4 Ds": Dermatitis, Diarrhea, Dementia, Death). ### Why This Patient Has Thiamine Deficiency This rural woman with a rice-based diet (polished rice lacks thiamine) and **isolated sensory neuropathy with positive Romberg sign** (vibration sense loss) fits the thiamine pattern perfectly. The absence of dermatitis rules out niacin deficiency. **High-Yield:** Thiamine deficiency → **sensory neuropathy** (Wernicke-Korsakoff in alcoholics); Niacin deficiency → **pellagrous dermatitis + diarrhea + dementia** (the 4 Ds). **Clinical Pearl:** Romberg sign positivity (loss of proprioception/vibration sense) is characteristic of thiamine-deficient neuropathy and dorsal column involvement. ### Mnemonic for Niacin Deficiency **4 Ds of Pellagra:** Dermatitis, Diarrhea, Dementia, Death [cite:Park 26e Ch 10]