The role of biomarkers and imaging in Parkinson's disease.

The diagnosis of Parkinson's disease (PD) currently relies on the appearance of certain clinical features. However, these features appear only years after the loss of nigral dopaminergic neurons. The progression of PD may be measured using clinical rating scales that are subjective and that have a variable inter-rater consistency. There is a growing need for a biomarker that will allow for early detection of the disease as well as provide a measure of disease progression. In this article, we review different biomarkers, with a focus on functional imaging techniques, which while imperfect, currently provide the best approach to this problem. We also discuss the use of structural imaging and emerging progress in other biochemical and molecular markers. While there is no single biomarker that will satisfy all requirements, a combination is likely to be of great use in identifying those subjects most likely to benefit from neuroprotective therapies, as well as in monitoring the effects of any interventions.