UNIQUE MYOCLONIC PATTERN IN CORTICOBASAL DEGENERATION

We describe two similar patients with a clinical diagnosis of corticob asal ganglionic degeneration (CBGD). After a period of increased actio n tremor, both patients developed a fixed posture in the right arm wit h a slow rhythmic myoclonus, which appeared to be caused by trains of highly synchronized and stimulus sensitive myoclonic discharges. Reset ting of the spontaneous myoclonic discharges by peripheral and central stimulation and a jerk-locked cortical potential were demonstrated in one case. The somatosensory evoked potentials (SEPs) showed abnormal parietal curves with small N20-P25 amplitudes and without giant SEP ch aracteristics. The latencies of the cortical event and of the late res ponses, and the duration and distribution of the discharges compare be st with those of the cortical reflex type of myoclonus. Localized pari etal cortical damage, as indicated by clinical evidence and imaging te chniques, may well explain the absence of a giant SEP in these patient s with CBGD.