What is the cause of pellagra?

Pellagra is a nutritional disorder caused by a deficiency of niacin, which results in dermatitis, dementia, and diarrhea. The dermatitis may occur in a photodistribution, consisting of vesicles, papules, erosions, and hyperpigmentation. The diagnosis is by clinical findings, as biopsy is nondiagnostic. In developed countries, patients at risk for pellagra include alcoholics and those on isoniazid therapy.