Low Frequency Repetitive Transcranial Magnetic Stimulation Can Reduce Action Myoclonus

Felix R. Wedegaertner, Marjorie A. Garvey, Leonardo G. Cohen, Mark Hallett, Eric M. Wassermann
Tuesday April 15 3:00 pm / Exhibit Hall A

To see whether treatment with low-frequency repetitive transcranial magnetic stimulation (rTMS) can decrease myoclonus.

rTMS in the single Hz range can safely produce decreases in the excitability of the primary motor cortex which last for several minutes (Wassermann et al. Electroenceph Clin Neurophysiol, 1996). 1 Hz amygdala stimulation inhibits kindling and blocks seizures in rats (Weiss et al. Neuroreport, 1995). Myoclonus results from deficient cortical inhibition which might be improved with low-frequency stimulation.

We studied three subjects with cortical action myoclonus and little or no myoclonus at rest. Two had posthypoxic encephalopathies, one had MERRF syndrome. rTMS was administered through a round coil at 110% of motor evoked potential (MEP) threshold and a frequency of 1 Hz for 30 min to the optimal scalp position for producing MEPs in the hand. EMG was monitored continuously during stimulation. Myoclonus was measured with an accelerometer attached to the subjects' right index and middle fingers. Acceleration in the vertical plane was recorded over five 20 s epochs while the subject held the arms and hands outstretched. The total RMS power in the spectrum from 0 to 20 Hz was used as a measure of the degree of myoclonus. Measurements were made before, immediately after, and at two, four and six hours after stimulation on each day of treatment. Stimulation was administered every 24 hours for five days (two subjects) or three days (one subject). Two subjects also received sham stimulation (single blind) for three days prior to active stimulation. This was identical to active stimulation, but was delivered over the occipital cortex where it produced auditory and scalp sensations, but no MEPs.

There were no side effects of rTMS in any subject. All three subjects showed marked decreases in RMS power after rTMS over the primary motor cortex. Across subjects, RMS power decreased by an average of 33.4% immediately after stimulation. When pooled across treatment days, this change was significant

These preliminary data indicate that 1 Hz rTMS can suppress abnormal excess cortical activity and produce brief but clear reductions in action myoclonus. Although these subjects did not realize a significant clinical benefit, changes in the treatment regimen may make this kind of treatment more useful in the future.

Sponsored by: NINDS intramural funding.

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