How accurately can Parkinson's disease be diagnosed?

The clinical picture of Parkinson's disease (PD) can be so varied that absolute clinical diagnosis may not always be possible. Several diverse entities (including toxins, pharmacologic agents, and multisystem atrophies and other degenerative diseases) can produce clinical syndromes almost indistinguishable from those of PD. Nevertheless, a sufficient number of guiding criteria--such as the presence of at least two of three motor signs (tremor, bradykinesia, and rigidity), persistence of these signs for several years, and responsiveness to levodopa--may serve to clarify and specify diagnosis, at least until such time as a biologic marker of PD is discovered. However, currently the clinical diagnosis of PD remains difficult.