Isoniazid in autoimmunity: a trigger for multiple sclerosis?

Isoniazid (INH) is a prodrug activated by the mycobacterial enzyme KatG, a multifunctional catalase peroxidase. KatG converts INH to reactive antimycobacterial species. For decades, an association between INH and drug-induced lupus erythematosus has been recognized. We present the case of a patient with primary progressive multiple sclerosis whose disease commenced weeks after initiating INH therapy for prevention of tuberculosis. Possible mechanisms by which INH may trigger autoimmunity in humans are discussed.