Pain in Parkinson's disease.

Pain, defined as an unpleasant or distressing sensory experience, has been recognized as feature of Parkinson's disease (PD) since the first descriptions of the disorder. Pain is estimated to occur in approximately 40% of patients with PD, and in a minority of individuals becomes severe enough to overshadow the motor symptoms of the disorder. Recent studies based on patients' descriptions of pain have enabled a classification of painful sensations into 1 or more of 5 categories: musculoskeletal pain, neuritic or radicular pain, dystonia-associated pain, primary or central pain, and akathitic discomfort. The existence of a central pain syndrome, intrinsic to PD, finds support in a collection of case reports, but the precise mechanism is unknown, and a correlation with pathology has not been made. This review describes the clinical features of the pain syndromes in PD, and provides a framework for evaluating, classifying, and treating painful symptoms in PD.