Neuroprotection and imaging studies in Parkinson's disease.

The most challenging issue when testing putative neuroprotective agents for Parkinson's disease (PD) in clinical trials is the assessment of the effect of the treatment on the neurodegenerative process. By measuring changes in symptoms severity, clinical rating scales represent an important tool to rate the progression of the disease. However, the rating of clinical symptoms is dependent on the examiner and the neuroprotective effect can be masked by the symptomatic effect of the therapy. 18F-dopa PET and 123I-beta-CIT SPECT have been shown to be able to monitor the progressive loss of presynaptic nigrostriatal projections in PD and have been used as surrogate biomarkers of disease in several recent clinical trials. In this article the value of imaging as a biomarker for testing neuroprotective agents in PD is reviewed.