Cortical hypometabolism assessed by a metabolic ratio in Parkinson's disease primarily reflects cognitive deterioration—[¹⁸F]FDG‐PET

Abstract

In Parkinson's disease patients with cognitive deterioration, regional cortical hypometabolism has been observed with [(18)F]fluorodeoxyglucose-positron emission tomography (FDG-PET). Our aim was to develop a robust method to subsume the overall degree of metabolic deterioration in Parkinson's disease by means of a single index and to investigate which of the clinical features correlates best with hypometabolism. Twenty-two Parkinson's patients (10 demented) and seven controls underwent FDG-PET. A metabolic index (mean relative uptake in typically affected regions) was calculated for each patient and compared with scores for cognition [Minimental State Examination (MMSE)], motor performance [Unified Parkinson's Disease Rating Scale (UPDRS III)" and behavior (Neuropsychiatric Inventory). In stepwise linear regression analysis, MMSE (P < 0.001) score showed the only significant effect. Estimated sensitivity and specificity for DSM-IV diagnosis of dementia were high for the metabolic index (MI), with 91 and 100%. Taken together, the presented data indicate that cerebral hypometabolism in Parkinson's disease is primarily associated with cognitive impairment.

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“…To obtain a single metabolic index from each PET scan to quantify the overall degree of disease-related metabolic deterioration, we used a concept known as metabolic ratio (23,24). Here, we generated the mask of affected regions by combining all clusters of significant hypometabolism detected with SPM.…”

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“…Cerebral glucose metabolism reflects cortical activation and synaptic density 26. Several studies associate this hypometabolism with cognitive impairment, suggesting that hypometabolism in PD primarily reflects cognitive deterioration 27, 28. Though a very recent postmortem study suggests that loss of synaptic markers predicts cognitive decline in Lewy body diseases,29 to the best of our knowledge, no direct links have been established between reduced glucose metabolism in PD and independent synaptic markers.…”