A 38-year-old man from northern India presents with a 4-month history of dermatitis on sun-exposed areas (face, neck, hands), chronic diarrhea, and mood disturbances including irritability and poor concentration. He works as a laborer and his diet consists mainly of corn and legumes. On examination, he has a well-demarcated erythematous rash with scaling on the dorsal surfaces of his hands and face. His serum albumin is 2.8 g/dL. What is the most likely vitamin deficiency?

Explanation

## Clinical Diagnosis: Niacin (Vitamin B3) Deficiency — Pellagra ### Classic Presentation: The "4 Ds" **Key Point:** Pellagra presents with the classic tetrad of **Dermatitis, Diarrhea, Dementia, and Death** (if untreated). This patient exhibits the first three. ### Clinical Features in This Case **Dermatological:** - Well-demarcated erythematous rash on sun-exposed areas (Casal's collar distribution on neck and dorsal hands) - Symmetric, photosensitive distribution - Scaling and potential hyperpigmentation **Gastrointestinal:** - Chronic diarrhea (niacin is essential for GI mucosal integrity) **Neuropsychiatric:** - Mood disturbances (irritability, poor concentration) - Early signs of dementia (confusion, memory loss in advanced cases) **Nutritional Risk Factors:** - Corn-based diet (corn niacin is in bound form, not bioavailable unless alkali-treated) - Low protein intake (tryptophan → niacin conversion impaired) - Low serum albumin (2.8 g/dL, indicating protein-energy malnutrition) ### Biochemistry & Pathophysiology **High-Yield:** Niacin is a precursor for NAD^+^ and NADP^+^, essential cofactors in energy metabolism and DNA repair. 1. **Primary sources of niacin:** - Dietary niacin (preformed) - Tryptophan → niacin conversion (60 mg tryptophan = 1 mg niacin) 2. **Deficiency consequences:** - Impaired oxidative metabolism → diarrhea, dermatitis - Neuronal dysfunction → dementia, peripheral neuropathy - Impaired DNA repair → skin and mucosal breakdown ### Diagnostic Confirmation | Test | Finding | |------|----------| | Serum niacin | <0.3 mg/100 mL | | Urinary N^1^-methylnicotinamide | <1.6 mg/24 hrs (reduced) | | Tryptophan levels | Often low | | Albumin | Low (protein malnutrition) | **Clinical Pearl:** The photosensitive distribution of the rash is a key diagnostic clue — UV exposure exacerbates the dermatitis in niacin deficiency, unlike other vitamin deficiencies. ### Mnemonic for Pellagra Signs **"4 Ds + Casal's Collar":** - **D**ermatitis (photosensitive) - **D**iarrhea - **D**ementia - **D**eath (if untreated) - **Casal's collar:** Symmetric rash on neck and upper chest ### Management 1. **Acute:** Niacin 500 mg PO daily or IV (nicotinamide preferred to avoid flushing) 2. **Dietary:** Increase protein, fortified grains, meat, eggs, legumes 3. **Monitor:** Neuropsychiatric recovery (may be incomplete if prolonged) 4. **Prevention:** Fortification programs in at-risk populations ### Geographic & Epidemiological Context **High-Yield:** Pellagra is endemic in parts of rural India, particularly in populations with corn-dependent diets and low protein intake. It is a public health concern in low-income regions.