A 18-month-old boy from rural Maharashtra presents with his mother complaining of poor feeding and irritability for the past 3 months. On examination, he has generalized hyperpigmentation of sun-exposed areas, a sharply demarcated erythematous rash over the dorsal hands and feet with crusting, and angular cheilitis. His gums are swollen and bleeding. Developmental milestones are delayed. Hemoglobin is 9.2 g/dL. Which vitamin deficiency best explains this clinical picture?

Explanation

## Clinical Diagnosis: Pellagra (Niacin Deficiency) ### Key Clinical Features Presented The constellation of findings—hyperpigmentation in sun-exposed areas (photosensitive dermatitis), sharply demarcated erythematous rash on dorsal hands and feet ("glove and stocking" distribution), angular cheilitis, gum swelling with bleeding, poor feeding, and developmental delay—is pathognomonic for **niacin (vitamin B3) deficiency** or pellagra. ### The "4 Ds" of Pellagra **Mnemonic: 4 Ds** — Dermatitis, Diarrhea, Dementia, Death - **Dermatitis**: Photosensitive, sharply demarcated rash in sun-exposed areas (dorsal hands, feet, neck, face) - **Diarrhea**: Gastrointestinal involvement (poor feeding, malabsorption) - **Dementia**: Developmental delay, neuropsychiatric symptoms - **Death**: If untreated, fatal outcome ### Pathophysiology **Key Point:** Niacin (vitamin B3) is an essential cofactor for NAD^+^ and NADP^+^, which are critical for: - Cellular energy metabolism (glycolysis, TCA cycle, oxidative phosphorylation) - DNA repair and synthesis - Skin barrier function and immune response Deficiency impairs energy production in rapidly dividing cells (skin, GI mucosa, nervous system), leading to the characteristic triad of dermatitis, GI dysfunction, and neurological manifestations. ### Risk Factors in Indian Context - Predominantly cereal-based diet (maize, sorghum, millet) with low bioavailable niacin - Malabsorption syndromes (chronic diarrhea, celiac disease) - Protein-energy malnutrition (PEM) - Chronic alcoholism (rare in children but relevant epidemiologically) ### Diagnostic Confirmation - **Urinary niacin metabolites** (N^1^-methylnicotinamide) — low in deficiency - **Serum niacin levels** — though not routinely done - **Clinical response to niacin supplementation** — rapid improvement within days ### Management - **Niacin supplementation**: 50–100 mg/day in divided doses (oral) - **Dietary counseling**: Fortified cereals, legumes, meat, eggs, groundnuts - **Treatment of underlying malabsorption** if present - **Response**: Rash typically clears within 1–2 weeks; neurological symptoms improve more slowly ### Differential Reasoning | Feature | Niacin Deficiency | Vitamin A | Vitamin C | Vitamin D | |---------|-------------------|-----------|-----------|----------| | **Photosensitive dermatitis** | ✓ (hallmark) | ✗ | ✗ | ✗ | | **Angular cheilitis + gum bleeding** | ✓ | ✗ | ✓ (but no rash) | ✗ | | **Developmental delay** | ✓ (from energy deficit) | ✓ (from infection risk) | ✗ | ✓ (from hypocalcemia) | | **Hyperpigmentation in sun-exposed areas** | ✓ (pathognomonic) | ✗ | ✗ | ✗ | | **Anemia** | Mild (secondary) | ✓ (from infection) | ✓ (from bleeding) | ✗ | **High-Yield:** The **sharply demarcated, photosensitive dermatitis** in a malnourished child is the single most discriminating feature for niacin deficiency. No other vitamin deficiency presents this way. ### Clinical Pearl **Pellagra is a disease of poverty and malnutrition.** In India, it remains endemic in regions dependent on low-niacin cereals (maize, sorghum) without dietary diversification. Recognition is critical because it is entirely preventable and reversible with supplementation.