Left Temporal Hypometabolism in FDG-PET underlines Cognitive Reserve Hypothesis in Frontotemporal Dementia

Introduction: Frontotemporal lobar degeneration as the second
most cause of presenile dementia shows a characteristic
pattern of hypometabolism in frontal and temporal regions
in [18F]-fluordeoxyglucose positron-emission-tomography
(FDG-PET). In ageing and dementia, the concept of cognitive
reserve as a mediating factor between neuronal injury and
clinical symptoms has been proposed for many years. Years of
education (YoE) has been demonstrated as a proxy of cognitive
reserve in Alzheimer’s disease. We aimed to test how the
paradigm of cognitive reserve is reflected in FTD. Subjects and
methods: FDG-PET of 93 subjects (age 68 ± 9 years) with FTD
were analysed retrospectively. Mini-mental-state-examination
(MMSE) and YoE were recorded. A voxel-wise regression analysis
was used to identify regional glucose metabolism associated
with declining MMSE. Individual FDG-PET values were extracted
from the resulting significant cluster (FWE correction, p < 0.05).
The residuals of the partial correlation between FDG-PET and
MMSE were correlated with YoE. Results: Cognitive deterioration
(MMSE) was only correlated with left temporal hypometabolism
whereas the contralateral temporal lobe and bilateral
frontal cortices did not indicate significant associations. Regression
analysis with values deriving from the left temporal cluster
indicated a significant positive association with MMSE (β =
0.62, p < 0.001). The residuals of the correlation of FDG-PET and
MMSE showed a significant correlation with the YoE (ß = 0.29,
p = 0.005). Conclusion: Cognitive decline is mainly associated
with left temporal hypometabolism in FTD. Cognitive reserve
expressed by a higher level of education is also present in FTD
and needs to receive attention as a potential modifying factor in
prevention and treatment of FTD.