The significance of defining preclinical or prodromal Parkinson's disease.

A body of clinical and pathologic evidence supports the concept that there a pre-Parkinson state exists prior to the time when Parkinson's disease (PD) can be formally diagnosed. The ability to define a the preclinical or prodromal PD state has many important implications. First, understanding the timing and sequence of pathologic change that occurs in PD could provide important clues as to the etiology and pathogenesis of PD, and provide insight into cell vulnerability factors. Second, defining a population of patients with preclinical PD would provide a potentially important group of subjects for clinical trials attempting to define disease-modifying therapies. And, finally, being able to determine that a person has PD at an earlier time point than is currently possible would permit the introduction of a putative disease-modifying therapy at a time when it could have more profound and long-lasting effects. This paper reviews the clinical significance of defining preclinical PD.