Medication Responsiveness of Motor Symptoms in a Population-Based Study of Parkinson Disease

We assessed degree of Parkinson disease motor symptom improvement with medication among subjects enrolled in an ongoing, population-based study in Central California. The motor section of the unified Parkinson disease rating scale (UPDRS) was performed on subjects in both OFF and ON medication states, and difference between these scores was used as an indicator of symptomatic benefit. Higher OFF minus ON scores correlated with more severe baseline symptoms. There was equivalent improvement on the motor UPDRS scale for subjects divided according to medication classes used: levodopa alone 7.3 points, levodopa plus other medications 8.5 points, and dopamine agonists but not levodopa 6.1 points. In addition, there was no difference in the magnitude of improvement when subjects were divided according to Parkinson disease subtype, defined as tremor dominant, akinetic-rigid, or mixed. In this community-based sample, these values are within the range of a clinically important difference as defined by previous studies. 1. Introduction Clinical trials in Parkinson disease document improvement of motor features of the disorder using standardized rating scales, in particular the unified Parkinson disease rating scale (UPDRS). However, subjects participating in these studies generally seek care in tertiary care centers; due to strict procedures implicit in the conduct of clinical trials, such subjects’ medications and response to medications are optimized and tightly controlled. To assess PD motor symptom control in a community-dwelling population, we used a cohort of PD subjects followed in a population-based study of PD risk and predictors of progression [1]. These subjects reside in rural counties in Central California, and their PD care is managed by local general neurologists [1]. Subjects were examined by movement disorder specialists using UPDRS Motor exams in the OFF state and again after their PD medication dosage (ON exam) as prescribed by their community clinician. The difference in Motor UPDRS scores between the OFF and ON states was used to document the degree of PD symptom improvement. It has been previously established by Shulman and colleagues that Motor UPDRS OFF-ON differences are clinically important with ranges of 2.3–2.7 points for minimal CID (clinically important difference) and 10.7–10.8 for large CID [2]. We investigated whether the Motor UPDRS OFF-ON differences found in our study were within these ranges and if the degree of improvement was associated with any factors in particular. Comparisons were made according to medication class used