Procainamide-induced myasthenia-like weakness and dysphagia

A 64-year-old man with chronic renal insufficiency was hospitalized with dysphagia and inability to keep his head erect 11 months after beginning procainamide hydrochloride (PA) for control of atrial flutter. Evaluation revealed esophageal dysmotility, worsening renal function, and elevated serum PA and N-acetylprocainamide (NAPA) concentrations. No evidence of autoimmune myasthenia gravis was found. PA was discontinued and normalization of PA and NAPA concentrations was associated with a decrease in muscle weakness and resolution of dysphagia. The correlation between clinical findings and serum concentrations of PA and NAPA suggests that drug excess due to impaired clearance was the basis for this unusual adverse drug reaction.