Variability in amplitude of untreated essential tremor.

Tremor amplitude was monitored in untreated patients with essential tremor by a procedure designed to minimise fluctuations due to factors known to influence tremor. Tremor was measured hourly for 6 hours in 14 patients and on five to seven occasions (separated by at least a week) in 22 patients. A wide range of within-patient variability was found, with some patients showing little and others showing considerable fluctuations in amplitude over the series of recordings. There was no simple relationship between variability and mean amplitude, frequency, age, duration of tremor or response to a single oral dose of propranolol. Variability did not differ between males and females or between patients with and without a family history of tremor. Diurnal fluctuations showed no consistent pattern. Long-term assessment revealed a significant trend towards lower amplitudes on successive occasions. To overcome systematic bias in data collection, clinical trials in essential tremor should employ large numbers of patients and rigorous randomisation of treatments in cross-over designs.