Characterizing Premotor Parkinson's Disease: Clinical Features and Objective Markers.

Increasingly, it has been recognized that in order to affect underlying neurodegeneration in Parkinson's disease (PD), individuals must be identified before onset of the classic motor symptoms. Thus, for research purposes, a redefinition of PD has been proposed into preclinical, premotor, and motor phases. In the preclinical phase, no clinical signs or symptoms of PD are present. In the premotor phase, nonmotor manifestations are detectable. These include olfactory, neuropsychiatric, sleep, gastrointestinal, and autonomic changes. A multi-modal approach is needed to maximize both sensitivity and specificity of any assessment of the premotor phase. To that end, several objective markers, such as dopaminergic imaging and electrophysiologic techniques, exist and are of potential utility. This review discusses the candidate nonmotor features and potential objective measures that may be used to define the premotor phase of PD.