Objective: To examine the frequency, temporal development, and stability of objectively derived motor changes during placebo treatment in PD and to define the clinical domains and demographic groups most affected. Background: Placebo effects are documented in neurology, but the timing and specific disabilities most susceptible to changes during placebo treatment in PD have not been examined. Methods: The authors examined the placebo-treated group from a randomized, multicenter, placebo-controlled clinical trial of monotherapy ropinerole in PD patients without motor fluctuations. In 105 patients, they evaluated placebo-associated effects on the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS), dividing the motor examination into four categories: tremor, bradykinesia, rigidity, and gait/balance/midline functions. The motor UPDRS and its subscales were compared over time (at baseline and at 4, 12, and 24 weeks) using Wilcoxon's signed rank test. They applied a rigorous definition of placebo-associated improvement as an improvement over baseline score in motor UPDRS of at least 50% or a change in at least two motor items at any one visit by greater than or equal to 2 points. Results: During the 6-month study, 16% of subjects improved on placebo treatment. The prevalence of response was steady (8 to 9%) at any one visit without a predominance of an early effect. No patient showed a placebo-associated improvement on all visits. All domains of parkinsonian disability were subject to placebo-associated improvement, with a trend toward more response in bradykinesia and rigidity than in tremor or gait/balance/midline function. Gender, age, disease duration, and baseline disability score did not influence the likelihood of improvement in association with placebo treatment. Conclusion: Based on a rigorous definition of placebo-associated improvement, prominent improvements in objective measures of PD disability occur during clinical trials. Because placebo-associated improvements occur throughout a 6-month trial, placebo-controlled studies in PD should be at least 6 months to capture early as well as late improvements.
