Essential tremor: electrophysiological and pharmacological evidence for a subdivision.

Forty five patients with essential tremor have been investigated by means of clinical examination, polygraphic EMG records and testing of long-latency reflexes. Clinically there were no differences between the patients, whereas the electrophysiological investigations suggested two subtypes. One group of patients may be characterised by normal long-latency reflexes and synchronous tremor bursts in antagonists or activity of the antigravity muscle alone. The second group had abnormal long-latency reflexes and reciprocal EMG activity in antagonists. It is suggested that these two groups represent distinct subgroups of essential tremor. Patients of the first group responded well to propranolol, whereas those of the second group did not.