Parkinson's disease: chameleons and mimics.

Parkinson's disease (PD) is a common neurodegenerative condition that usually presents with symptoms related to asymmetric bradykinesia, resting tremor, rigidity and postural instability. Making the correct diagnosis can be challenging as many conditions-including tremor, gait and atypical parkinsonian disorders-can mimic PD. PD can present with unanticipated motor and non-motor symptoms, and so can masquerade as a number of rheumatological, neurological, sleep and mood disorders. Careful clinical assessment, informed by well-validated diagnostic criteria, is important in the initial diagnostic formulation. In uncertain or ambiguous cases, follow-up with monitoring of the treatment response usually gives the correct diagnosis, as validated in postmortem follow-up studies. 'Premotor' PD-a range of non-motor symptoms, particularly sleep disorders and constipation, which can occur up to 20 years before PD motor onset-is common. The presence of non-motor features in early disease sometimes supports the diagnosis of PD. Here we give an overview of the diagnosis of PD and its most important chameleons and mimics, and review the recent advances in structural and functional imaging in parkinsonism.