Occipital hypoperfusion and motor reserve in Parkinson's disease: an early-phase 18F-FP-CIT PET study

Abstract

Individual variability exists in parkinsonian motor symptoms despite a similar degree of nigrostriatal dopamine depletion in Parkinson's disease (PD), called motor reserve. We enrolled 397 patients newly diagnosed with PD who underwent dual-phase ¹⁸F-FP-CIT PET upon initial assessment. Individual motor reserve was estimated based on initial parkinsonian motor symptoms and striatal dopamine transporter availability using a residual model. Patients with low motor reserve (the lowest quartile group, n = 100) exhibited decreased uptake in the occipital region compared to those with high motor reserve (the highest quartile group, n = 100) on early-phase ¹⁸F-FP-CIT PET images. Patients with high motor reserve had a lower risk of conversion to dementia than the those with low motor reserve, whereas the effect of PD groups on the risk of dementia conversion was not mediated by occipital hypoperfusion. These findings suggest that cerebral hypoperfusion in the occipital region is associated with low motor reserve in patients with PD.

Fig. 1. PD groups according to motor reserve estimates.

A Scatter plots of the natural logarithm of DAT availability in the posterior putamen and UPDRS-III scores. The general linear model was used to predict UPDRS-III scores based on age, sex, disease duration, and the natural logarithm of DAT availability in the posterior putamen. The solid line (black) indicates the regression line of the general linear model and the dotted lines (red) indicate the range of the highest and lowest quartiles of fitted values. Red = PD-MR-H group. Green = PD-MR-I group. Blue = PD-MR-L group. B Comparison of the regional uptake in early-phase ¹⁸F-FP-CIT PET images among the PD groups. The PD-MR-L group exhibited more severely decreased uptake in the occipital region compared with the PD-MR-H group.

Fig. 2. Motor reserve and dementia conversion in PD.

A Kaplan–Meier curves to estimate the occurrence of dementia after the onset of parkinsonian symptoms in patients with PD. The PD-MR-L group (n = 100) has a higher risk of dementia conversion than that of the PD-MR-H group (n = 100; P_Log-rank = 0.027). The risk of dementia conversion of the PD-MR-I group (n = 197) does not differ from that of the PD-MR-H (P_Log-rank = 0.115) and PD-MR-L (P_Log-rank = 0.291) groups. The crosses in the graphs indicate censored data. B Mediation analysis to determine the relationship between PD groups, regional cerebral perfusion, and the risk of PDD conversion. PD groups (PD-MR-H and PD-MR-L groups) and regional cerebral perfusion (SUVRs in the occipital region) were entered as a predictor and mediator, respectively. A mediation analysis was performed while controlling for the effects of age of parkinsonian symptom onset, sex, natural logarithm of DAT availability in the posterior putamen, education level (in years), and K-MMSE scores. Direct effects of PD groups were significant, while indirect effects through occipital perfusion were not significant. HR hazard ratio, β regression coefficients, SE standard error.