Background and objective: Multicenter study aiming at investigating the characteristics of cognitive decline, neuropsychiatric symptoms, and brain imaging in individuals with subjective cognitive decline (SCD) and subtle cognitive decline (pre-Mild Cognitive Impairment, pre-MCI).

Methods: Data were obtained from the Network-AD project (NET-2011-02346784). The included subjects underwent baseline cognitive and neurobehavioral evaluation, FDG-PET, and, amyloid-PET. We used Principal Component Analysis (PCA) to identify independent neuropsychological and neuropsychiatric dimensions and their association with brain metabolism.

Results: A total of 105 subjects (SCD=49, pre-MCI=56) were included. FDG-PET was normal in 45% of subjects and revealed brain hypometabolism in 55%, with a frontal-like pattern as the most frequent finding (28%). Neuropsychiatric symptoms emerging from the Neuropsychiatric Inventory and the Starkstein Apathy Scale were highly prevalent in the whole sample (78%). An abnormal amyloid load was detected in the 18% of the subjects that underwent amyloid-PET (n=60). PCA resulted in three neuropsychological factors: 1) executive/visuo-motor, correlating with hypometabolism in frontal, occipital cortices and basal ganglia; 2) memory, correlating with hypometabolism in temporo-parietal regions; 3) visuo-spatial/constructional, correlating with hypometabolism in fronto-parietal cortices. Two factors emerged from the neuropsychiatric PCA: 1) affective, correlating with hypometabolism in orbito-frontal, cingulate cortex, insula; 2) hyperactive/psychotic, correlating with hypometabolism in frontal, temporal and parietal regions.

Discussion: FDG-PET evidence suggests either normal brain function or different patterns of brain hypometabolism in SCD and pre-MCI subjects. These results indicate that SCD and pre-MCI represent heterogeneous populations. Consistently, different neuropsychological and neuropsychiatric profiles emerged, which correlated with neuronal dysfunction in specific brain regions. Long-term follow-up studies are needed to assess the risk of progression to dementia in these conditions.