[A case of familial essential myoclonus and epilepsy with suspected focus in the hemisphere ipsilateral to myoclonus limbs].

A 50-year-old man who first noticed shaking of the hands at age of 18 and had previous history of three convulsive episodes was admitted to our department because of the generalized tonic seizure with loss of consciousness. Family history showed that 7 members had similar shaking and one had generalized seizure. On neurological examination, rhythmic myoclonic jerks were noted in the bilateral upper limbs, and was remarkably more severe on the left. Other neurological findings were normal. Based on the benign clinical course, familial history, and the normal range of pyruvate and lactate levels in serum and cerebrospinal fluid, we diagnosed familial essential myoclonus and epilepsy (FEME)/benign adult familial myoclonic and epilepsy (BAFME). After admission, we performed electrophysiological test. EEG showed spike discharge mainly in the left parietooccipital lobe. Jerk-locked back averaging (JLA) showed spikes 30 msec precedings the trigger in the left parietooccipital lobe. Because JLA spikes are commonly found 20 msec precedings the trigger, we consider the subtraction time of 10 msec was due to the conduction through the corpus callosum. Some reports showed that in progressive myoclonus epilepsy patients, transcallosal excitation of one hemisphere by the other was critical for generalized seizure. In cases of FEME/BAFME, epileptic focus in the hemisphere ipsilateral to the myoclonus limbs has not previously reported. Our case suggested that generalization of the seizure was caused by the interhemispheric excitation through the corpus callosum.