Clinical features, diagnosis, and imaging of parkinsonian syndromes.

The differential diagnosis of parkinsonian syndromes continues to challenge clinicians. The clinical diagnosis of idiopathic Parkinson's disease is correct in only about three quarters of cases when reevaluated neuropathologically, emphasizing the need for more discriminative diagnostic criteria. The clinical spectrum of brain stem Lewy body idiopathic Parkinson's disease itself may be heterogeneous, including dementing and nondementing, familial and sporadic, and levodopa-responsive and -nonresponsive subgroups. Recent clinicopathologic evidence suggests that other parkinsonian syndromes such as progressive supranuclear palsy may also be neuropathologically heterogeneous. Pharmacologic criteria of dopaminergic responsiveness have no absolute power of differentiating between idiopathic Parkinson's disease and other parkinsonian disorders, although an absent response argues against idiopathic Parkinson's disease. The best diagnostic imaging criteria still come from positron emission tomography studies of the functional integrity of the nigrostriatal dopaminergic system, but more widely applicable techniques are needed. Promising perspectives for this have come form studies of D2-receptor binding with iodobenzamide single photon emission computed tomography in parkinsonian syndromes.