Procainamide-induced myositis.

The risk of developing a syndrome resembling lupus erythematosus when taking procainamide has been well recognized for over 15 years, although the development of myopathy has been reported on one occasion only, in this instance without histopathological evidence of muscle inflammation. The patient reported in this paper developed a severe, rapidly progressive vasculitis, apparently limited to muscle, after taking procainamide for 42 months, his myopathy remitting rapidly after withdrawal of the drug and a short course of treatment with azathioprine. Although this man had no clinical evidence of SLE, he had impressive immunological evidence to support this diagnosis.