Prevalence of essential tremor in patients with Parkinson's disease vs. Parkinson-plus syndromes.

Clinical literature suggests an association between essential tremor (ET) and Parkinson's disease (PD), and recent pathological studies describe Lewy bodies in some ET patients. If some ET were an expression of Lewy body disease, one could hypothesize that ET patients who develop parkinsonism would more likely develop PD (a Lewy body disease) than non-Lewy body forms of parkinsonism. The objective was to compare the proportions of patients with PD vs. Parkinson-plus syndromes who had diagnoses of ET. Retrospective chart review at the Neurological Institute (NI) of New York. A larger proportion of the 210 PD than 210 Parkinson-plus syndrome patients had kinetic tremor on examination (119 [56.7%] vs. 70 [33.3%], P < 0.001). Patients with PD were more likely to have a prior diagnosis of ET than were patients with Parkinson-plus syndromes (7.1% vs. 2.4%, OR 3.16, 95% CI 1.13-8.85, P = 0.02) and more likely to have a diagnosis of ET assigned by an NI neurologist (5.3% vs. 0.0%, OR 12.85, 95% CI 1.66-99.8, P = 0.001). Patients with PD were three to thirteen times more likely to have diagnoses of ET than were patients with Parkinson-plus syndromes. These data further confirm the link between ET and PD, and possibly, between ET and Lewy body disease.