Comparison of impaired subcortico-frontal metabolic networks in normal aging, subcortico-frontal dementia, and cortical frontal demential

Normal aging, progressive supranuclear palsy (PSP), and frontotemporal deme ntia (PID) are characterized by different degrees of decline in frontal lob e functions. We used (18)FDG-PET and statistical parametric mapping (SPM96) to compare relative subcorticofrontal metabolic impairment at rest in 21 h ealthy elderly subjects (HES), 20 PSP patients, and 6 FTD patients. When HE S were compared to 22 healthy young subjects, widespread decrease in metabo lism was observed in bilateral medial prefrontal areas including anterior c ingulate cortices, in dorsolateral prefrontal areas, in left lateral premot or area, in Broca's area, and in left insula. In PSP compared to the 43 hea lthy subjects (HS), we observed subcorticofrontal-metabolic impairment incl uding both motor and cognitive neural networks. Impairment of functional co nnections between midbrain tegmentum and cerebellar, temporal and pallidal regions was demonstrated in PSP as com pared to HS. When comparing FTD to H S, glucose uptake was primarily reduced in dorsolateral and ventrolateral p refrontal cortices and in frontopolar and anterior cingulate regions. There was also bilateral anterior temporal, right inferior parietal, and bilater al striatal hypometabolism. Finally,FTD showed more severe striatofrontal m etabolic impairment than PSP, while mesencephalothalamic involvement was on ly observed in PSP. Our data suggest that subcorticofrontal metabolic impai rment is distributed in distinct subcorticocortical networks: in normal agi ng, PSP, and PTD. Subcorticofrontal dementia in PSP is related to hypometab olism in discrete frontal areas, which are probably disconnected from certa in subcortical structures. The concept of subcortical dementia is reinforce d by our data, which show disrupted functional connections between mesencep halon and cerebellar cortex, inferior and medial temporal regions, and pall idum. (C) 1999 Academic Press.