Assessment of Parkinson disease: what do we need to show neuroprotection?

To date, no pharmacological agent has convincingly demonstrated the ability to slow the progression of Parkinson disease (PD). The development of treatments that slow down the progressive degeneration of the nigrostriatal dopaminergic system (true neuroprotection), which is ultimately responsible for the patients' functional decline, has become one of the basic goals of PD research. In this review, we have attempted to analyze the role of different methods that measure PD severity (basically, clinical scales, timed tests, and neuroimaging techniques) in the evaluation of the "neuroprotection" provided by different types of treatment for the disease, on the basis of clinical evidence.