IDIOPATHIC GENERALIZED MYOKYMIA

Idiopathic generalized myokymia (IGM) is a rare, heterogeneous, and po orly understood syndrome. We present analysis of 75 reported cases in the world literature. IGM affects men and women equally, with a mean a ge of onset 29 +/- 19 years. Patients' common presenting complaints ar e stiffness (60%), cramps (12%), weakness (12%), and muscle twitching (4%). Family history is positive in 30%. In addition to generalized cl inical myokymia (92%), abnormal neurologic findings include: hyporefle xia (70%), weakness (45%), grip myotonia (39%), and calf hypertrophy ( 16%). Electrical activity consisting of spontaneous continuous motor u nit activity and/or electrical myokymia was documented in all patients . When electrical myokymia was observed (66%), the grouped discharges where irregular and had an interburst frequence of 2-300 Hz. Both phen ytoin and carbamazepine are effective treatments. We conclude that IGM has a wide spectrum of symptoms and severity and should be considered in all patients that present with stiffness, cramps, or muscle twitch ing. EMG greatly aids in diagnosis. (C) 1994 John Wiley and Sons, Inc.