A case of myotonic dystrophy associated with sick sinus syndrome

A 22-year-old man with myotonic dystrophy associated with sick sinus syndrome is described. The patient showed marked weakness of grasping power, grip myotonia, percussion myotonia, bilateral cataracts, fixed facial expression and elevation of serum CPK level, and was diagnosed as having myotonic dystrophy. The Holter ECG showed marked sinus bradyarrhythmia at the rate of 25 beats per minute and the sinus node recovery time using overdrive suppression test was significantly prolonged. These findings indicated the patient also suffered from the sick sinus syndrome. Although various kinds of ECG abnormalities have been noted in the cases with myotonic dystrophy, there have been very few descriptions concerning the involvement of sinus node dysfunction in this disorder.