Motor signs in the prodromal phase of Parkinson's disease.

Relatively subtle deterioration of the motor system likely occurs well before the patient meets established motor criteria for a clinical diagnosis of Parkinson's disease; ie, the occurrence of at least 2 of the cardinal motor deficits: bradykinesia, rigidity, tremor, and/or postural instability. Powerful compensatory mechanisms may mask these clinical symptoms and make them difficult to identify and evaluate in the earliest stages of the illness. This review summarizes our current knowledge of motor signs that are thought to occur in the prodromal phase of Parkinson's disease and suggests how motor assessment batteries could be designed to detect these subclinical motor deficits with a high degree of accuracy and sensitivity.