Potassium iodide in the treatment of erythema nodosum and nodular vasculitis.

Twenty-nine patients with erythema nodosum, nodular vasculitis, or erythema nodosum-like lesions associated with Behçet's syndrome were treated with potassium iodide. Administration of the drug for systemic effect showed a substantial effect in 11 of 15 patients with erythema nodosum, seven of ten with nodular vasculitis, and one of four with leg lesions of Behçet's syndrome. Relief of subjective symptoms, including tenderness, joint pain, and fever, occurred within 24 hours. Substantial improvement in the eruption occurred within a few days, and the lesions disappeared completely ten to 14 days after therapy was initiated. The patients to whom the medication was administered shortly after the initial onset of erythema nodosum seemed to respond most satisfactorily. The effect of the drug was marked in the patients with positive C-reactive protein reactions, joint pains, and/or fever. Possible mechanisms by which potassium iodide exerts its effect are discussed.