CLINICAL-FEATURES, DIAGNOSIS, AND IMAGING OF PARKINSONIAN SYNDROMES

The differential diagnosis of parkinsonian syndromes continues to chal lenge clinicians. The clinical diagnosis of idiopathic Parkinson's dis ease is correct in only about three quarters of cases when reevaluated neuropathologically, emphasizing the need for more discriminative dia gnostic criteria. The clinical spectrum of brain stem Lewy body idiopa thic Parkinson's disease itself may be heterogeneous, including dement ing and nondementing, familial and sporadic, and levodopa-responsive a nd -nonresponsive subgroups. Recent clinicopathologic evidence suggest s that other parkinsonian syndromes such as progressive supranuclear p alsy may also be neuropathologically heterogeneous. Pharmacologic crit eria of dopaminergic responsiveness have no absolute power of differen tiating between idiopathic Parkinson's disease and other parkinsonian disorders, although an absent response argues against idiopathic Parki nson's disease. The best diagnostic imaging criteria still come from p ositron emission tomography studies of the functional integrity of the nigrostriatal dopaminergic system, but more widely applicable techniq ues are needed. Promising perspectives for this have come form studies of D2-receptor binding with iodobenzamide single photon emission comp uted tomography in parkinsonian syndromes.