Pellagra (Niacin Deficiency)

Pellagra is the clinical syndrome of severe niacin (vitamin B3) deficiency, manifesting as the classic four D's: dermatitis, diarrhea, dementia, and death if untreated. Niacin (nicotinic acid and nicotinamide) is essential for NAD/NADP coenzymes involved in oxidative metabolism and DNA repair, and a fraction is synthesized endogenously from dietary tryptophan.

Primary pellagra occurs when diet is dominated by maize without alkali processing (nixtamalization), historically epidemic in the southern United States and parts of Africa. Secondary pellagra arises in alcoholism, malabsorption, anorexia, prolonged isoniazid therapy, carcinoid syndrome, Hartnup disease, and chronic dialysis where niacin or tryptophan is depleted.

Diagnosis is clinical with confirmation by low urinary N-methylnicotinamide and 2-pyridone, plus rapid response to therapy. Management is oral nicotinamide 100-300 mg/day for adults (preferred over nicotinic acid because it lacks flushing) plus a balanced diet rich in B vitamins, with treatment of the underlying cause and rehydration in severe diarrhea.