Epileptic negative myoclonus: An EEG-single-photon emission CT study indicating involvement of premotor cortex.

We report a combined EEG-single-photon emission CT (SPECT) study on a patient with epileptic negative myoclonus (ENM). Clinically, the ENM was characterized by brief repetitive lapses in postural tone of the right upper extremity when the arms were held outstretched, whereas no movement effect was observed during rest. Ictal EEG showed repetitive left frontal spikes with a maximum at electrodes EC1 and F1. EMG silent periods lasting from 100 to 200 ms followed the onset of the EEG transients by a latency of 20 to 40 ms. The N20 component of median nerve somatosensory evoked potentials-representing a biological marker of the location of central fissure-showed a phase reversal between electrodes P3 and C1 and thus was located considerably posterior to the spike maximum. We obtained accurate anatomic reference of cerebral blood flow changes visible on SPECT by a special coregistration technique of MRI and SPECT. SPECT performed during ENM showed a marked regional hyperperfusion in the left middle frontal gyrus and a less pronounced increase in tracer uptake in the left supramarginal gyrus. Our results suggest that ENM is generated by epileptic activity in the premotor area in the middle frontal gyrus corresponding to Brodmann's area 6.