Trial designs used to study neuroprotective therapy in Parkinson's disease.

There have been numerous trials conducted to evaluate putative disease-modifying or neuroprotective treatments in Parkinson's disease. These trials have used several different study designs and outcome measures. Each of these has its own strengths and weaknesses. Confounding all studies is the potential symptomatic benefit that the treatment might have on the features of Parkinson's disease. In addition, patient-related factors such as age of onset and the nature of the dominant symptoms may have important impacts that are often not addressed. Here we provide an overview of the various trial designs that have been used and emphasize the challenges faced in attempting to study neuroprotection in Parkinson's disease and the advances needed before this goal can be successfully achieved.