In ETPD patients, the mean total Unified Parkinson's Disease Rating Scale (UPDRS) score at the diagnosis of PD was 20 [+ or -] 6.2 (14-26), which favored early PD.
Compared to ET patients, ETPD patients were older (p=0.03).
However, there is no agreement among movement disorders specialists for ETPD. Determining the differences between ET patients and ETPD patients may contribute to better understanding of the underlying pathogenic mechanisms of ET and to investigating the possible existence of a subset of ET predisposing to PD.
Contrary to two studies (10,21), investigating ETPD patients and in which male predominance was observed, and to the generally accepted idea, our finding was consistent with a more recent study reported by Spanaki et al.
In Chaudhuri series (9) with 13 ETPD patients presenting with asymmetric postural tremor at the onset of ET, the mean latency was 19.2 years.
In our series, we found increased incidence for family history of ET in ET patients than in ETPD patients.
There are different data in the literature regarding the rate of ETPD patients among PD patients.
Although one-fourth of ET patients had head tremor, all ETPD patients had no head tremor.