Immediate placebo effect in Parkinson's disease--is the subjective relief accompanied by objective improvement?

A recent well-conducted meta-analysis showed that placebo effect is associated with a possible small benefit for subjective outcomes, but has no significant effects on objective outcomes.

Herein, we aimed to investigate the immediate effects of two different types of placebo [placebo pill and sham transcranial magnetic stimulation (TMS)] in Parkinson's disease (PD) patients and compared them to the standard treatment (levodopa) in a proper randomized, double-blind, crossover clinical trial.

PD patients received three different interventions on different days: levodopa, placebo pill, and sham TMS. The motor function was assessed using simple and choice reaction time, Unified Parkinson's Disease Rating Scale (UPDRS), finger tapping, Purdue Pegboard test, time to button up, walking time and supination-pronation. The subjective motor function was measured by a visual analogue scale (VAS).

The results showed that there was a significant motor function in the motor function only after the treatment with levodopa, but not after treatment with placebo pills or sham TMS. However, patients reported a similar subjective improvement in motor function indexed by VAS following these three treatments.

These results suggest that placebo interventions in PD may have an immediate subjective sensation of improvement but result in no significant objective motor changes compared with levodopa treatment. Although physiological changes are possible after a placebo intervention, our findings suggest that the acute placebo effect in PD may be the result of the subjective change in the motor rating only.