## Pellagra: The 4 Ds **Key Point:** Pellagra is caused by niacin (vitamin B₃) deficiency and presents with a pathognomonic clinical triad of **dermatitis, diarrhea, and dementia** — often remembered as the "4 Ds" (with death as the fourth if untreated). ### Dermatological Features - Symmetric, photosensitive dermatitis on sun-exposed areas (face, neck, hands, feet) - Lesions are sharply demarcated, erythematous, and may progress to hyperpigmentation - Classically described as a "glove and stocking" or "necklace" distribution ### Gastrointestinal Manifestations - Diarrhea (often severe and bloody) - Glossitis and stomatitis - Abdominal pain and anorexia ### Neuropsychiatric Features - Dementia (cognitive decline, confusion, memory loss) - Peripheral neuropathy - Psychosis, depression, irritability - Encephalopathy in severe cases ### Biochemical Basis Niacin (tryptophan metabolite) is essential for NAD⁺/NADP⁺ synthesis, critical cofactors in oxidative metabolism. Deficiency impairs energy production in high-metabolic tissues (skin, GI tract, CNS). **High-Yield:** The "4 Ds" mnemonic — **D**ermatitis, **D**iarrhea, **D**ementia, **D**eath — is frequently tested in NEET PG. ### Epidemiology in India Pellagra remains endemic in parts of rural India, particularly in populations with corn-dependent diets low in bioavailable niacin and tryptophan. [cite:Park 26e Ch 8]
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