Somatosensory evoked high-frequency oscillation in Parkinson's disease andmyoclonus epilepsy

Aim: A high-frequency oscillation in the range of 600-900 Hz has been shown to be a component of the somatosensory evoked potential (SEP) in humans. I n the present communication, we studied these oscillation potentials in two neurological disorders. Subjects and methods: Subjects were 20 healthy volunteers, 17 patients with Parkinson's disease (PD) and 3 with myoclonus epilepsy (ME). Median nerve SEPs were recorded using filters set at 0.5 and 3000 Hz. Several peaks of o scillation were obtained by digitally filtering raw SEPs from 500 to 1000 H z, and their amplitudes and onset latencies were measured. Results: In normal subjects, several oscillation potentials were observed a t the latency of 0 to 8 ms after the onset of N20. In PD patients, the osci llation potentials at normal latencies were significantly larger than those of normal subjects. Moreover, in 7 of 17 PD patients, they were extremely enlarged (>mean +/- 3 SD of normal values). In contrast, in patients with M E, abnormally enlarged oscillation potentials were seen at longer latencies (7-14 ms) in spite of normal-sized early oscillation potentials. Magnetoen cephalographic analyses showed that any oscillation potentials originated f rom the primary sensory cortex. Conclusions: There are at least two mechanisms for producing the oscillatio n potentials of SEP. Those around N20 have some relation with the basal gan glia function and are enlarged in PD patients, the others around P25-N33 ar e enhanced in ME patients. (C) 1999 Elsevier Science Ireland Ltd. All right s reserved.