[Status of cerebral cortical excitability in juvenile myoclonus epilepsy].

The myoclonic epilepsies constitute an heterogeneous group of entities characterized by primary generalized seizures, whose common critical manifestation is myoclonus. Within this group there is a subset of patients, identified by Janz in 1955 as "Impulsive petit mal" and later named "Janz juvenile myoclonic epilepsy" (JJME) by Delgado-Escueta. Its most important clinical features are myoclonus, expressed as mild to moderate jerks of neck, shoulders and arms. These jerks are more frequent when awakening; they can be caused by sleep deprivation and emotional stress, without consciousness impairment. Usually neurologic examinations and mental status are normal. Response to specific treatment is good, with disappearance of seizures in most patients. We attempted to assess the pathophysiologic mechanisms involved in this kind of epilepsy. The existence of differences or similarities with the findings described in the other forms of myoclonic epilepsy was specially considered. In 14 patients with JJME, we performed C reflex studies with negative results. The mean amplitude of somato sensitive evoked potential (SSEP) was around 5 microV (normal values: 2.5 microV) in its different components. Shibasaki et al. suggested that the amplitude increase could be related to a cortical excitability increase at the somatosensory and motor level, which is the probable site of the epileptogenic area. Within the patient group with myoclonic progressive epilepsy (EMP) and continuous partial epilepsy (CPE), SSPEs amplitude ranged from 8 microV to 40 microV. In our patient group, the increase in SSPEs amplitude was smaller than the one observed in the other two entities. However, it was significantly higher than the mean value for the normal population.(ABSTRACT TRUNCATED AT 250 WORDS)