Myoclonus in Alzheimer's disease and minipolymyoclonus.

The typical electrophysiological correlates of myoclonus in Alzheimer's disease are similar to those of cortical reflex myoclonus, with a focal, contralateral negativity in the EEG preceding the myoclonic jerk. One difference from cortical reflex myoclonus is that the duration of the negativity is longer and its onset before the jerk earlier. The features differ from those described for subacute spongiform encephalopathy and should be helpful for differential diagnosis. The electrophysiological correlate of minopolymyoclonus that can be seen in Alzheimer's disease and in other pathological states is a bifrontal negativity in the EEG that precedes the myoclonic jerk. This new type of electrophysiological correlate of myoclonus may reflect activity of a subcortical generator.