The Clinical Profile of Tremor in Parkinson's Disease

Background: Tremor is one of the most troublesome manifestations of Parkinson's Disease (PD) and its response to dopaminergic medication is variable; an evidence-based framework of PD tremor is lacking yet needed to inform future investigations. Objective: To perform a comprehensive longitudinal analysis on the clinical characteristics, course and response to dopaminergic medication of tremor in de-novo PD. Methods: Three hundred ninety-seven participants were recruited in the Parkinson Progressive Markers Initiative, a prospective observational cohort study in early de-novo PD. Rest, postural and kinetic tremor scores were extracted from the Movement Disorders Society-Unified Parkinson's Disease Rating Scale. Progression from baseline to 7-year follow-up of rest, postural and kinetic tremor scores, and their response to in-clinic dopaminergic medication were analyzed through linear mixed-effects models adjusted for age, sex and disease duration at enrollment. A sensitivity analysis was conducted through subgroup and imputation analyses. Results: 382 (96.2%) participants showed tremor and 346 (87.2%) showed rest tremor in at least one assessment over 7 years. Off-state rest, postural and kinetic tremor scores increased significantly over time, coupled with a significant effect of dopaminergic medication in reducing tremor scores. However, at each assessment, tremor was unresponsive to in-clinic dopaminergic medication in at least 20% of participants for rest, 30% for postural and 38% for kinetic tremor. Conclusions: PD tremor is a troublesome manifestation, with increasing severity and variable response to medications. This analysis details the current clinical natural history of tremor in early-to-mid stage PD, outlining an evidence-based framework for future pathophysiological and interventional studies.