Early diagnosis of Parkinson's disease: recommendations from diagnostic clinical guidelines.

Therapeutic options for Parkinson's disease (PD) are currently limited to symptomatic agents. Levodopa is the most efficacious treatment; however, higher doses and long-term use are associated with adverse effects such as motor fluctuations and dyskinesia. Early treatment of PD with other agents such as dopamine agonists and monoamine oxidase type B inhibitors can provide symptomatic benefit and delay initiation of levodopa therapy. Early treatment of PD is contingent upon early and accurate diagnosis of the disease, which can be challenging because there are no biomarkers or neuroimaging or other clinical tests available to confirm the diagnosis. PD diagnosis is currently based on the presence or absence of various clinical features and the experience of the treating physician. A definitive diagnosis can be made only after autopsy. Moreover, the signs and symptoms present in early PD can resemble those of a number of other movement disorders, particularly other forms of parkinsonism, such as multiple system atrophy, drug-induced parkinsonism, and vascular parkinsonism, as well as diffuse Lewy body disease and essential tremor. Nevertheless, diagnosis of PD based on clinical features and response to antiparkinsonian medication can be achieved with a fairly high level of accuracy, particularly when made by a physician specializing in movement disorders. This article reviews and summarizes published recommendations for the clinical diagnosis of PD.