Impact of cognitive reserve in frontotemporal dementia illustrated by FDG-PET.

Objectives: Frontotemporal lobar degeneration is the second most presenile cause of dementia. [¹⁸F]-fluordeoxyglucose positron-emission-tomography (FDG-PET) is widely used to underline the diagnosis by a characteristic pattern of hypometabolism in frontal and temporal regions. As shown for Alzheimer’s disease, years of education (YoE) can serve as a proxy of cognitive reserve, moderating the association between cognitive function and the severity of neurodegeneration detected by FDG-PET. However, corresponding data for frontotemporal dementia (FTD) are limited. Thus, we aimed to test if the impact of cognitive reserve is as well reflected in FTD.

Methods: FDG-PET of 77 subjects with FTD were analysed retrospectively. Mini-mental-state-examination (MMSE) and YoE were recorded. Statistical parametric mapping (SPM) was used to identify regions of hypometabolism in FTD patients versus cognitively healthy controls (HC) and to perform correlation analysis of FTD patients with MMSE. Individual FDG-PET values were extracted from a cluster including significant voxels in the correlation analysis and served for multiple regression analysis with age, MMSE and YoE as covariates. Results: When compared to HC, FTD patients showed a widespread bilateral fronto-temporal hypometabolism (p < 0.001). Cognitive deterioration measured by the MMSE correlated highly with hypometabolism in the right hemispheric temporal lobe (p < 0.001). Regression analysis of the right temporal cluster indicated a significant positive association with MMSE (β = 0.62, p < 0.001) and a negative association with YoE (β = -0.29, p < 0.001). In contrast to that, the contralateral temporal lobe and bilateral frontal cortices did not indicate significant associations. Conclusions: Cognitive decline is mainly associated with right temporal hypometabolism in FTD. Cognitive reserve due to a higher level of education is also present in FTD and needs to be considered for interpretation of FDG-PET scans.

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