Modulation of symptomatic palatal tremor by magnetic stimulation of the motor cortex

Objectives: Magnetic stimulation of the motor cortex can be used to determi ne the involvement of the cortex in rhythmic movement disorders. Symptomati c palatal tremor (SPT) is thought to come from a pacemaker that is relative ly resistant to internal and external stimulation. In this study, we invest igated the effect of magnetic stimulation of motor cortex on SPT. Methods: Five male patients, aged 67-79 years, with SPT after brain stem in farction or hemorrhage, all had a synchronous mouth angle twitch with the p alatal movement. Electromyographic activity was recorded with a monopolar n eedle electrode from orbicularis oris. In experiment 1, transcranial magnet ic stimulation (TMS) was delivered at 200% motor threshold (MT) to reset SP T. In experiment 2, the effect of TMS intensities was studied at 80-240% MT in two SPT patients. To determine the influence of the TMS, we used the re setting index (RI). Results: TMS reset the tremor in all 5 SPT patients at 200% MT with RIs of 0.86-0.96. The latency of the tremor reappearance after TMS was longer than the pre-stimulus tremor interval, and the intervals between the subsequent tremor bursts were also prolonged. The degree of tremor resetting was clos ely correlated with the magnetic stimulus intensity and the latency of the tremor reappearance after TMS. Conclusions: Stimulation of the motor cortex may modulate the generator of SPT. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.