The relationship of essential tremor to other movement disorders: report on 678 patients. Essential Tremor Study Group.
We examined 678 essential tremor patients in specialty, university, and private practice clinics. The mean age of patients was 65.2 years with a similar number of men and women. Six percent of patients were left-handed. A positive family history of tremor was reported in more than 60% of patients. Alcohol ingestion was reported to decrease tremor in 74% of patients who were cognizant of the effect of alcohol on tremor. Mean age at tremor onset was 45.3 years. An earlier onset of tremor was observed in those patients having a positive family history of tremor. Tremor affected the hands in 90% of patients, head in 50%, voice in 30%, and legs and chin in 15%. Functional disability was common and impairment at work occurred in 18%. Propranolol and primidone were the most frequently used drugs and were effective in 40% of patients. Six and one-tenth percent of essential tremor patients had concomitant Parkinson's disease, 6.9% had a coexisting dystonia, and 1.8% had myoclonus. It is concluded that the frequency of Parkinson's disease in essential tremor is more than would be reported in the general population and that other movement disorders are infrequently observed in essential tremor.