Method of Tremor Levodopa Responsiveness Assessment and Its Correlation With Clinical Factors in Parkinson's Disease: Outcomes of the Acute Levodopa Challenge Test.

Abstract

Objectives: Levodopa remains the most effective treatment for Parkinson's disease (PD); however, tremor reactions to dopaminergic medications show significant variance among patients with PD. This study aimed to assess the different methodologies employed to determine the dopamine responsiveness of tremors and their association with the clinical characteristics of PD. Methods: Patients with PD and tremors were evaluated using the acute levodopa challenge test (LCT). Tremor levodopa responsiveness (LR) was calculated using the Unified Parkinson's Disease Rating Scale Part III (UPDRS-III) scores during OFF and ON periods. Tremor LR was calculated in two formats: absolute difference in tremor scores (OFF-ON), termed aLR, and percentage change in tremor scores, termed %LR and calculated as ([OFF-ON]/OFF100%). Independent variables were compared between the better tremor response to levodopa and poorer tremor response to levodopa groups based on the tremor change rate median score. Additionally, the effect of the tremor LR calculation method was correlated with clinical measures. Results: This study enrolled 188 patients with PD who displayed tremors, of whom 98 (52%) showed better tremor response to levodopa. We identified a moderately negative correlation between tremor aLR and the rigidity-to-tremor score ratio (r = 0.40) during the OFF period, in addition to positive correlations between tremor aLR and the tremor score (r = 0.75), rest tremor score (r = 0.75), motor score (r = 0.42), postural and kinetic tremor score (r = 0.30), and tremor score-to-disease duration ratio (r = 0.30) of the UPDRS-III during OFF periods. The tremor %LR showed no significant relationship with any of the tested variables. Conclusions: The aLR, rather than the %LR, is a more effective assessment method for evaluating the efficacy of levodopa for treating tremors in PD.