Emergence of Parkinson's disease in essential tremor: A study of the clinical correlates in 53 patients

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Abstract
Patients with essential tremor (ET) may develop Parkinson's disease (PD); however, few studies have examined the clinical features of this combination syndrome. Fifty‐three patients with ET‐PD were studied and compared to 53 PD and 150 ET patients. Although the latency from onset of ET to PD was brief (20 years). The gender distribution of ET‐PD (67.9% male) was identical to that of PD (67.9% male), yet differed from that of ET (50.0% male) (P = 0.02). The initial cardinal sign of PD was rest tremor in 100% of patients. In ET‐PD, the side of greatest initial ET severity usually matched that of greatest PD severity (P < 0.05). In ET‐PD, male gender predominated and the sidedness of the ET and PD usually matched. The co‐occurrence of the two diagnoses in the same patient may be mechanistically related. © 2008 Movement Disorder Society