Overview of the extranigral aspects of Parkinson disease.

In recent years, there has been increasing recognition of the features of Parkinson disease that are not related to nigrostriatal dopamine deficiency. This review addresses selected clinical, anatomic, pathologic, and biochemical correlates of the early premotor symptoms of Parkinson disease, later nonmotor fluctuations, and advanced dopa-unresponsive motor and nonmotor features. The recognition of early features that predate classic motor symptoms will be important as effective neuroprotective therapy becomes available. Later-stage features often contribute markedly to disability and impaired quality of life and, therefore, represent an important future therapeutic challenge.