Tremor Is Highly Responsive to Levodopa in Advanced Parkinson's Disease

Background: Tremor in Parkinson's disease (PD) is commonly regarded as less responsive to levodopa than bradykinesia and rigidity, with levodopa-resistant PD tremor considered relatively common. Objective: The aim was to assess the levodopa responsiveness of tremor, bradykinesia, and rigidity in a population with advanced PD. Methods: We performed a retrospective study of 526 people with PD screened for deep brain stimulation. Results: Levodopa's Cohen's d effect sizes were in the same order of magnitude for the 3 cardinal motor symptoms. Proportional improvement in tremor (86.8%) was higher than bradykinesia (45.7%) and rigidity (67.0%) (P < 0.0001). Full resolution was more frequent for tremor (67.9%) than for bradykinesia (0.4%) or rigidity (24.8%) (P < 0.0001). Levodopa-unresponsive tremor, defined as improvement less than 25%, was documented only in 4.0%, as opposed to 19.4% for bradykinesia and 9.8% for rigidity (P < 0.0001). Conclusions: In advanced PD, tremor was more responsive to levodopa than bradykinesia and rigidity, and levodopa-unresponsive tremor was relatively rare.