Significance of parkinsonian manifestations in essential tremor.

Parkinsonian features, notably resting tremor may be seen in some essential tremor patients but the significance of those is unknown. The reported risk of parkinsonism in essential tremor patients varies from being unchanged to 35 times higher than expected. We studied 9 patients with essential tremor who had autopsies. In 6 of the 9 (66%) resting tremor was noted and in 3 (33%) cases fully developed parkinsonism was noted. The parkinsonism was consequent to neuroleptic usage in 2 and to basal ganglia status lacunaris and cribrosus in one case but no consistent abnormalities were noted in 3 essential tremor only and 3 essential tremor plus resting tremor cases. We conclude that resting tremor is an age-related natural evolution in some essential tremor patients. We recommend that the additional diagnosis of parkinsonism in the essential tremor be made only when resting tremor, bradykinesia and rigidity are all evident. The risk of ideopathic Parkinson's disease in essential tremor cases is similar to the general population.