Dapsone-induced motor polyneuropathy. A complication of prolonged treatment of subcorneal pustular dermatosis.

A motor polyneuropathy developed in a woman with subcorneal pustular dermatosis of 16 years' duration, who had received at least 300 gm of dapsone over a five-year period and 80 gm during the four-month period of progression of her neurologic symptoms. Although the patient believed her muscle power had returned to normal four months after the drug was stopped, a slight peripheral neuropathy remained. Electrodiagnostic and clinical features during the period of greatest weakness and the subsequent 16 months were consistent with a polyneuropathy of the axonal type. The neurotoxicity of dapsone appears to be dose-dependent, but the mechanism by which it occurs is unknown.