Disassociation between fluctuation shift over frequency and glucose metabolism in motor cortex of Parkinson’s disease: a hybrid PET/fMRI study

Increased glucose metabolism and decreased low-frequency fluctuation have been consistently reported in the motor area of Parkinson's disease (PD). The reason for such seeming paradox is unclear. Here, we enrolled 34 PD patients and 25 healthy controls (HCs) for hybrid PET/fMRI scan (PET/fMRI(discovery) dataset). In addition, 2 replication datasets, namely fMRI(validation-1) and fMRI(validation-2) dataset, were also included. We computed ratio of standard uptake value (SUVr) to measure FDG-uptake. The amplitude of low-frequency fluctuations (ALFF) for the following 4 frequency bands was calculated: slow-5, slow-4, slow-3, and slow-2. We obtained a significant group-by-frequency interaction effect of ALFF in the paracentral lobule/supplementary motor area (PFWE = 0.003) and the right sensorimotor area (PFWE < 0.001) in the PET/fMRI(discovery) dataset, which could be replicated using fMRI(validation-1) and fMRI(validation-2) datasets (PFWE < 0.05). In detail, HCs exhibited power law-like fluctuation pattern, but PD patients did not. Correlation analyses further revealed significant associations between ALFF and FDG-uptake in HCs (P-values < 0.031), but not in PD (P-values > 0.28). Taken together, this study identified a fluctuation shift over frequency effect in PD patients, which further disassociated with glucose metabolism in the motor cortex.