A 38-year-old woman from rural Maharashtra presents with a 3-month history of progressive weakness, numbness in her feet, and difficulty walking. On examination, she has a stocking-glove distribution of sensory loss, absent ankle reflexes, and mild atrophy of intrinsic foot muscles. Her diet consists mainly of polished rice and minimal protein intake. Blood glucose is normal. Nerve conduction studies show demyelination. Which vitamin deficiency is most likely responsible for her neurological findings?

Explanation

## Clinical Presentation Analysis The patient presents with a classic peripheral neuropathy characterized by: - **Polished rice diet** — the hallmark dietary risk factor for thiamine (B1) deficiency - Stocking-glove sensory distribution - Absent deep tendon reflexes (ankle jerks) - Mild intrinsic muscle atrophy - Normal blood glucose (excludes diabetic neuropathy) - **Demyelinating pattern on nerve conduction studies** ## Vitamin B1 (Thiamine) Deficiency — The Diagnosis **Key Point:** Thiamine (Vitamin B1) deficiency causes **dry beriberi**, presenting as a peripheral neuropathy with sensory loss in a stocking-glove distribution, absent reflexes, and distal muscle weakness/atrophy. This is the classic presentation in populations subsisting on **polished (milled) rice**, which strips the bran layer where thiamine is concentrated. **High-Yield:** Thiamine deficiency in India is common due to: - Polished/milled rice as the dietary staple (thiamine lost in milling) - Minimal dietary protein and micronutrient diversity - Prolonged cooking of rice (further destroys thiamine) - Chronic alcoholism (impaired absorption and utilization) ## Pathophysiology of Thiamine Neuropathy Thiamine pyrophosphate (TPP) is an essential cofactor for: 1. **Pyruvate dehydrogenase** — entry of pyruvate into TCA cycle 2. **α-Ketoglutarate dehydrogenase** — TCA cycle intermediate step 3. **Transketolase** — pentose phosphate pathway Deficiency → impaired oxidative metabolism in neurons → energy failure → axonal degeneration with secondary demyelination → peripheral neuropathy (dry beriberi). ## Why B1 and Not Other B Vitamins? | Vitamin | Neuropathy Type | Key Distinguishing Feature | |---------|-----------------|---------------------------| | **B1 (Thiamine)** | **Dry beriberi** — peripheral neuropathy; Wernicke-Korsakoff (CNS) | **Polished rice diet**; stocking-glove, absent reflexes, demyelination | | **B3 (Niacin)** | Pellagra (4 Ds: dermatitis, diarrhea, dementia, death) | Photosensitive dermatitis and GI symptoms are prominent | | **B6 (Pyridoxine)** | Sensory neuropathy (typically from megadose toxicity) | Rapid onset with high-dose supplementation; dorsal root ganglion damage | | **B12 (Cobalamin)** | Subacute combined degeneration (SCD) | Posterior column + pyramidal signs; vegetarian diet or malabsorption history | **Clinical Pearl:** The combination of **polished rice diet** + **stocking-glove neuropathy** + **absent ankle reflexes** + **distal muscle atrophy** is the textbook presentation of **dry beriberi** (thiamine deficiency). While B12 deficiency also causes demyelinating neuropathy, the dietary clue of polished rice and the absence of posterior column or pyramidal signs (e.g., no Babinski, no proprioception loss mentioned) strongly favor thiamine deficiency in this rural Indian context. ## Diagnostic Confirmation - Erythrocyte transketolase activity (low) — most sensitive functional test - Serum thiamine level (< 70 nmol/L) - Dramatic clinical improvement with thiamine supplementation (therapeutic trial) ## Treatment Thiamine 100 mg IV/IM immediately, followed by oral thiamine 10–25 mg three times daily. Nutritional rehabilitation with a balanced diet. Early treatment is reversible; delayed treatment may result in permanent neurological damage. [cite: Harrison 21e Ch 407; KD Tripathi Essentials of Medical Pharmacology 8e; Park's Textbook of Preventive and Social Medicine 25e]