Parkinson's disease with and without preceding essential tremor-similar phenotypes: a pilot study.

The aim of this pilot study was to compare clinical aspects of tremor-dominant Parkinson's disease (PD) patients with and without preceding essential tremor to identify characteristics of these two subgroups. Nineteen patients with diagnoses of both essential tremor (ET) and Parkinson's disease in comparison to 18 patients with tremor-dominant Parkinson's disease without preceding tremor were investigated. The profile of several motor and non-motor symptoms, including cognitive dysfunction, depression, sleep alterations, olfaction changes and some autonomic symptoms, as well as imaging aspects obtained by transcranial sonography were compared between groups. Parkinson's patients with essential tremor scored higher in kinetic and postural tremor items (p < 0.05) and displayed an enlarged third ventricle on transcranial sonography (p = 0.010), which was not found in tremor-dominant Parkinson's disease patients. All other motor and non-motor symptoms could not distinguish between either study group. Neither group showed a distinct clinical profile related to non-motor symptoms or symptoms other than tremor-specific motor aspects. The fact that non-motor symptoms were similar in ET-PD gives rise to the hypothesis that also the prodromal phase of PD is similar in ET patients later developing classical PD compared to individuals developing PD without preceding ET. This hypothesis needs to be followed in prospective studies to verify whether the establishment of an ET subgroup with prodromal markers for PD is feasible.