Neurophysiology of orthostatic tremor. Influence of transcranial magnetic stimulation

A 74-year-old patient suffers from painful muscle cramps when he stands since 30 years. He has no visible tremor but 16 Hz burst activity on EMG, indicating orthostatic tremor. Previous diagnosis was hysteria, stiff person syndrome or dystonia. This shows that EMG during standing should be part of the examination of patients with stiff muscles or muscle cramps. Tremor was not strictly orthostatic. It appeared in back muscles while sitting, when the patient supported a weight with outstretched arms. Phase between muscles differed between normal standing and standing on heels. Subthreshold transcranial magnetic stimulation modulated timing of the tremor bursts and inhibited them at higher intensity stimulation.