Examining the motor phenotype of patients with both essential tremor and Parkinson's disease

The subset of patients with essential tremor (ET) that develops Parkinson's disease (PD) has not been fully clinically characterized.

Motor features were retrospectively reviewed in 18 ET patients who developed PD (ET→PD), 20 ET and 30 PD patients with similar ages and disease durations.

Fewer ET→PD than ET patients had widespread postural and/or action tremor (2/17 [11.8%] vs. 11/17 [64.7%]; p = 0.001) and marginally fewer had cerebellar signs (1/15 [6.7%] vs. 6/18 [33.3%], p = 0.06). ET→PD patients required fewer ET medications than did their counterparts with ET (p = 0.001). ET→PD patients and PD patients did not differ in UPDRS, Hoehn and Yahr, or Schwab and England scores (each p≥0.14).

ET patients who develop PD may have distinct pre-PD motor features compared to their counterparts with ET who do not develop co-existing PD. Prospective studies are needed to evaluate the predictive value of these clinical features for the emergence of PD.