fMRI language dominance and FDG-PET hypometabolism

Atypical language dominance is common in patients with temporal lobe epilepsy. We examined the association of left temporal hypometabolism with laterality of fMRI activation in a language task in a cross-sectional study.

Thirty patients with temporal lobe epilepsy (mean age 32.4 ± 11.0 years [range 18-55]; epilepsy onset 15.3 ± 11.3 years [range 0.8-40]; 22 left focus, 8 right focus) had (18)fluoro-deoxyglucose (FDG)-PET using noninvasive cardiac input function. After MRI-based partial volume correction, regional glucose metabolism (CMRglc) was measured and asymmetry index, AI = 2(l - R)/(L + R), calculated. fMRI language dominance was assessed with an auditory definition decision paradigm at 3 T. fMRI data were analyzed in SPM2 using regions of interest from Wake Forest PickAtlas (Wernicke area [WA], inferior frontal gyrus [IFG], middle frontal gyrus [MFG]) and bootstrap laterality index, LI = (l - R/L + R).

Nineteen patients had ipsilateral temporal hypometabolism; 3 of 4 patients with atypical language had abnormal FDG-PET. Increasing left midtemporal hypometabolism correlated with decreased MFG LI (r = -0.41, p < 0.05) and showed trends with WA LI (r = -0.37, p = 0.055) and IFG LI (r = -0.31, p = 0.099); these relationships became more significant after controlling for age at onset. Increasing hypometabolism was associated with fewer activated voxels in WA ipsilateral to the focus and more activated voxels contralaterally, but overall, activation amount in left WA was similar to subjects without left temporal hypometabolism (t = -1.39, p > 0.10).

We did not find evidence of impaired blood oxygenation level-dependent response in hypometabolic cortex. Regional hypometabolism appears to be a marker for the temporal lobe dysfunction that leads to displacement of language function.