Objective: To determine whether occipital reduction in regional cerebral glucose metabolism in PD reflects retinal versus nigrostriatal dopaminergic degeneration. We hypothesized that occipital glucose metabolic reduction should be symmetric if parkinsonian retinopathy is responsible for the reduction.
Methods: PD patients without dementia (n = 29; age 63 +/- 10 years) and normal controls (n = 27; age 60 +/- 12 years) underwent [18F]fluorodeoxyglucose PET imaging. Regional cerebral glucose metabolic rates were assessed quantitatively.
Results: When compared with normal controls, PD patients showed most severe glucose metabolic reduction in the primary visual cortex (mean -15%, p < 0.001). Occipital glucose metabolic reduction was greater in the hemisphere contralateral to the side of the body affected initially or more severely in PD. There was an inverse correlation between side-to-side asymmetries in finger-tapping performance and occipital glucose metabolic reduction (r = -0.45, p < 0.05; n = 28). The correlation was strongest in patients with a relatively early stage of PD with more unilateral motor impairment (Hoehn and Yahr stage I, r = -0.74, p < 0.01; n = 10).
Conclusion: The results indicate a pathophysiologic association between nigrostriatal dysfunction and occipital glucose metabolic reduction in PD.