[Presynaptic nigrostriatal function in Parkinson disease and Parkinson-plus syndromes. Comparative studies using positron emission tomography with L-6-(18F)fluorodopa].

L-6-[18F]fluorodopa PET is suitable to assess the presynaptic nigrostriatal function within the living human brain. The purpose of this study was to compare the striatal rate constant Ki for L-6-[18F]fluorodopa in patients with Parkinson's disease (PD), Parkinsonism plus syndromes (PPLUS) and controls. 27 patients (m: 13, f: 14) between 36 and 75 years and 20 controls (m: 10, f: 10) between 20 and 85 years were examined. The clinical severity of the akinesia and rigidity were rated on the modified Columbia scale. In patients with PD the mean value of Ki was determined to be 0.339 +/- 0.098 [ml/striatum/min], in PPLUS 0.161 +/- 0.083, and in controls 0.708 +/- 0.121. The values of Ki were significantly different among the three groups (P = 0.001, ANOVA). The side-to-side difference D % of Ki was calculated to be 9.1% +/- 6.8% in PD, 14.2% +/- 10.9% in PPLUS, and 5.1% +/- 5.5% in controls (P = 0.079 PD vs. controls, 0.172 PD vs. PPLUS, and P = 0.003 PPLUS vs. controls). Ki values and rating on the Columbia scale did not show a strong correlation in both PD and PPLUS. In conclusion, the presynaptic nigrostriatal function seems to be more affected in PPLUS compared with PD. These findings may support the hypothesis of a "levelling-off" of the dopaminergic function in PD.