CORTICAL REFLEX NEGATIVE MYOCLONUS

Three patients with progressive myoclonic epilepsy (PME), two of them clinically manifesting only negative myoclonus and the other manifesti ng both positive and negative myoclonus, were electrophysiologically i nvestigated, and compared with two other patients with PME presenting with only positive myoclonus. Electric stimulation of the median nerve during sustained active wrist extension in the three patients with ne gative myoclonus often elicited a short lapse of the posture in the st imulated hand associated with a silent period in the muscle discharge with or without being preceded by an abrupt increase in the muscle dis charge (C reflex). The occurrence of the stimulus-induced silent perio d was significantly correlated with that of the giant somatosensory ev oked potentials (SEPs), and in two patients the silent period was elic ited also in the opposite (non-stimulated) hand when the giant SEP was recorded at the hemisphere ipsilateral to the stimulus as well. In on e patient, the duration of the silent period was positively correlated with the amplitude of the cortical SEP. Furthermore, the duration of the induced silent period was closely related to the recovery function of SEP in each individual case. In contrast, in the two patients mani festing only positive myoclonus, the silent period was not elicited by the peripheral stimulation, and the somatosensory cortex was hyperexc itable immediately after the peripheral stimulus. Thus, this stimulus- sensitive negative myoclonus is mediated by a transcortical reflex mec hanism, and corresponds to the negative form of the cortical reflex my oclonus ('cortical reflex negative myoclonus').