Abstract

Isoniazid (INH) commonly causes pyridoxine deficiency. It can also cause niacin deficiency leading to pellagra, diagnosis of which is often delayed or missed. We report one such case of INH induced pellagra.

A 35 year old male patient with pulmonary tuberculosis on anti-tubercular therapy for 2 months containing isoniazid, rifampicin, pyrazinamide and ethambutol, presented with 2 weeks history of diarrhoea and rashes over his neck and all four limbs. Upon examination, he had hyperpigmented, hyperkeratotic symmetric plaques over the neck, dorsal surface of the feet, extensor surface of hands and forearms. Skin biopsy findings were consistent with Pellagra. Niacin 200mg/day for 2 weeks showed significant improvement in his condition.

Pellagra is a chronic systemic disease caused by deficiency of niacin, features of which are classically described as four D’s, diarrhoea, dermatitis, dementia and death. Dietary deficiency of tryptophan, chronic alcohol consumption, abnormalities of tryptophan metabolism and drug induced are the common causes of niacin deficiency. INH, being a structural analogue of niacin, suppresses endogenous niacin production especially in slow acetylators, thereby causes niacin deficiency. Simple oral supplementation of niacin is sufficient to improve the condition.

Keywords: Pellagra; Isoniazid; Tuberculosis; Niacin; Anti-tubercular therapy