Does abnormal neuronal excitability exist in myotonic dystrophy? I. Effects of the antiarrhythmic drug hydroquinidine on slow saccadic eye movements

The abnormal neuronal excitability hypothesized in myotonic dystrophy (MD) might contribute to psychomotor and behavioral disturbances of MD patients. To gain new insights into the pathophysiology of MD, we determined whether the antiarrhythmic drug hydroquinidine would ameliorate slow saccadic eye movements (SEMs), apathy and hypersomnia in MD patients. SEMs were selected as simple modality for psychomotor investigation. The study was conducted in a randomized, placebo-controlled, double-blind, crossover manner. Ten am bulatory patients without contraindications to hydroquinidine administratio n were enrolled. Hydroquinidine (450 mg/day) or placebo was given orally fo r 6 weeks with a washout period of 6 weeks between treatments. SEMs were re corded by electrooculography and analyzed by a computer system. Two patient s withdrew in the first week of active treatment because of nausea and epig astralgia. Hydroquinidine significantly increased the normalized peak sacca dic velocity and shortened the saccadic reaction time compared to placebo. The drug's effects on apathy and hypersomnia are presented in a companion p aper.