Clinical differentiation of parkinsonian syndromes: prognostic and therapeutic relevance.

Parkinson disease is the most common cause of parkinsonism, but other causes should always be excluded because they have a different prognosis, respond differently to medical treatment, and should not be managed by surgical means. However, diagnosis, even by experts, is challenging; one autopsy series showed an error rate of 24%. Distinction between various diagnostic possibilities depends on the history and examination findings. The use of certain medications, the rapid rate of disease progression, early onset of falling, the presence of certain dysautonomic symptoms, cognitive or behavioral changes, or a history of poor response to dopaminergic therapy may suggest an atypical form of parkinsonism. Postural hypotension, dementia, supranuclear ophthalmoparesis, or early postural instability should alert the examiner to consider an atypical cause of parkinsonism. Tests of autonomic function and brain imaging are often helpful in distinguishing these diseases.