Familial benign myoclonus epilepsy of adult onset : A previously unrecognized myoclonic disorder

Three families with a common clinical feature of adult onset myoclonus epilepsy were studied. Onset of the myoclonus, continuously presented and intensified by movement and emotional stress, was between the 3rd and 5th decades. Generalized seizures, following worsening of the myoclonus, occurred only a few times in life. This condition was considered to be an autosomal dominant trait with a high rate of penetrance. Although the symptoms gradually worsened with age in some cases, they were not associated with dementia or cerebellar disorder, distinguishing this condition from progressive myoclonus epilepsies (PMEs). Electrophysiologically, polyspikes on the electroencephalogram (EEG), giant wave in somatosensory evoked potentials, enhanced long-loop C reflexes and a preceding wave on jerk-locked back averaging of EEG were demonstrated, suggesting that the myoclonus originated in the cerebral cortices. This is a distinct hereditary disease different from PMEs, juvenile myoclonic epilepsy or other myoclonic disorders seen in adults.