Uncovering the hidden placebo effect in deep-brain stimulation for Parkinson's disease

To determine the magnitude of the placebo effect in deep-brain stimulation (DBS) for Parkinson's disease (PD).

The placebo effect in PD is related to the expectation of clinical benefit. Changes in expectation occurring in DBS crossover studies can be used to estimate the associated placebo effect. For example, the response to active-DBS is predicted to be greater in patients who have previously experienced the effect of placebo-DBS than in those without such an experience.

Data were obtained by searches of Medline and PubMed using three keywords: Parkinson's disease, deep-brain stimulation, and crossover study. Between-group comparisons of the effect of active-DBS were performed by t-test and analysis of covariance.

Data on 126 PD patients were available for analysis. These patients participated in a multicenter, two-period, placebo-controlled crossover study on the efficacy of DBS for PD. As predicted, active-DBS was found to be more effective when preceded by placebo-DBS (i.e. in the high expectation group) than when not (i.e. in the lower expectation group). The estimated magnitude of the placebo effect in DBS was equivalent to 39% of the magnitude of the effect of active-DBS.

There is a prominent placebo effect associated with DBS in PD. Crossover studies may be useful for estimating the placebo effect in other medical conditions.