Search

Previous reports have suggested that essential tremor (ET) represents a risk factor for the development of Parkinson's disease (PD). Patients with long-standing ET who develop PD tend to have a tremor-dominant subtype. To further clarify this association, we examined patients from kindreds with autosomal dominant ET who had signs of isolated PD but did not meet criteria for overlapping ET. We identified 22 patients with PD meeting these diagnostic criteria, and 90% (20 of 22) had tremor-predominant subtype of PD. Unilateral rest tremor was the presenting symptom in 15 of 22 patients, bradykinesia or rigidity in 5 of 22, and gait problems in 2 of 22. Postural tremor was relatively mild, and the severity of kinetic tremor tightly correlated with rest tremor (r = 0.83, P0.001). Tremor-dominant subtype of PD in patients with a positive family history of ET suggests that these patients have inherited a genetic susceptibility factor for tremor, which affects the motor phenotype of PD.

The presence of bilateral arm tremor is a key diagnostic feature of essential tremor (ET). We analyzed the presence of unilateral arm tremor in familial ET cohort of 133 autosomal dominant ET kindreds with 412 affected individuals. Inclusion criteria in patients with unilateral arm postural and/or kinetic tremor required the duration of tremor for at least 5 years, without hypokinetic-rigid syndrome, dystonic posturing, or history of sudden onset of tremor. Only subjects with at least one living first degree relative who met diagnostic criteria for definite ET were included. Eighteen subjects met the inclusion criteria and five had postural tremor only, while the majority (13/18) had a combination of postural and kinetic tremor. Our data shows that unilateral tremor associated with ET is relatively rare and can be identified in 4.4% patients in a cohort of familial ET.