Levodopa-induced local cerebral blood flow changes in Parkinson's disease and related disorders.

Local cerebral blood flow (CBF) in the steady state and after intravenous administration of levodopa (1 mg/kg) was measured by xenon-enhanced computed tomography in patients with Parkinson's disease (PD, n = 16), progressive supranuclear palsy (PSP, n = 6), olivopontocerebellar atrophy (OPCA, n = 5), and arteriosclerotic parkinsonism (AP, n = 7). Three patterns of local CBF changes following levodopa were observed: (1) diffuse CBF increases, especially in striatum and thalamus, as found in patients with PD; (2) no significant changes in CBF, as in patients with OPCA and AP; and (3) CBF reductions in basal ganglia and thalamus, as seen in patients with PSP. The CBF increases after levodopa in PD may be secondary to metabolic activation of the nigrostriatal dopaminergic system. The poor CBF responses in patients with OPCA, AP, and PSP appeared to reflect degeneration of the dopaminergic neurons and dopamine receptors to various degrees. The CBF increases, especially in striatum and thalamus, tended to be greater (not significant) among responders to oral levodopa therapy. Levodopa-induced CBF measurements may be useful for the differential diagnosis of parkinsonian syndromes of various etiologies, but are not necessarily sufficient for predicting outcomes of long-term levodopa therapy.