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The global burden of Parkinson’s disease is projected to increase in future decades as the number and proportion of older adults increases. This review addresses research advances since 1998, when the disorder was last reviewed in the Journal, and includes recently introduced concepts relevant to clinical practice. For two centuries, Parkinson’s disease has been diagnosed clinically on the basis of the characteristic motor syndrome of bradykinesia accompanied by resting tremor, rigidity, and postural reflex impairment, all largely the result of dopaminergic dysfunction in the nigrostriatal system. Advances in our understanding of the disease suggest that a biologic definition may be possible, but many questions remain. In this review, we use the clinical definition of Parkinson’s disease.
