Resetting of orthostatic tremor associated with cerebellar cortical atrophy by transcranial magnetic stimulation

Objectives: To investigate the resetting effects of transcranial magnetic s timulation over motor cortex on orthostatic tremor, characterized by high-f requency electromyographic discharges in weight-bearing muscles, particular ly orthostatic tremor (OT) associated with cerebellar cortical atrophy; and to compare our results with those obtained in primary OT, for which transc ranial magnetic stimulation does not reset tremor. Design: Study of 3 patients who clinically exhibited a sporadic pancerebell ar syndrome associated with isolated cerebellar atrophy and features of OT. Setting: Research hospital. Main Outcome Measures: Electromyograms and transcranial magnetic stimulatio n studies with a resetting index calculated on the basis of the timing of m easured bursts and predicted bursts for a magnetic stimulus given at increa sing delays. Results: Surface electromyographic recordings in weightbearing muscles show ed tremor with a frequency of 14, 15, and 14 Hz in the 3 patients. Transcra nial magnetic stimulus was able to reset OT. Resetting index was 0.72. Conclusions: Transcranial magnetic stimulus resets OT associated with cereb ellar cortical atrophy, emphasizing the role of motor cortex in the genesis of OT associated with a cerebellar dysfunction. Our results argue in favor of a distinct pathophysiological mechanism of primary OT and OT associated with cerebellar cortical atrophy.