Resting-state functional MRI (fMRI) helps to distinguish temporal lobe epilepsy (TLE) with mesial temporal sclerosis (MTS) from TLE without MTS. The findings, published in Epilepsia, validate the value of pre-surgical imaging in epilepsy evaluations.
The study, led by Karen Blackmon, PhD, of New York University, included 34 patients with TLE and 34 age- and sex-matched controls. MTS was confirmed through histologic evaluation of surgical tissue, resulting in 16 participants with TLE-MTS and 18 with TLE-noMTS.
Fractional amplitude of low-frequency fluctuations (fALFFs) in the blood oxygen level-dependent (BOLD) resting-state fMRI signal, which is a marker of metabolic demand at rest, were averaged in 5 brain regions: the hippocampus, amygdala, and frontal, temporal, and occipital lobes. Volume and cortical thickness estimates were also taken for each region. The regions were labeled ipsilateral or contralateral according to seizure lateralization, and then compared across all 3 groups.
The researchers found that the TLE-MTS group had reduced fALFF in the ipsilateral amygdala and hippocampus while the TLE-noMTS group had slightly reduced fALFF in the ipsilateral amygdala but not the hippocampus. Ipsilateral hippocampal volume accounted for 37% of the variance in MTS status (P<.001) while fALFF contributed 10% (P=.021). Two cases of MTS were accurately classified by fALFF but not volume, while 3 were classified with volume but not fALFF.
In patients with TLE-MTS, fALFF with global signal regression (GSR) at the lobar level was reduced in the ipsilateral temporal and bilateral frontal lobes; fALFF was reduced in the bilateral front lobes in patients with TLE-noMTS compared to normal cortical thickness.
“In our cohort, ipsilateral hippocampal volume and fALFF independently contributed to MTS classification, each metric accurately identified both overlapping and nonoverlapping cases,” the authors wrote. “This suggests that MTS patients without volume loss show functional abnormalities and that fALFF is sensitive to pathologic features of MTS that are partly independent from the well-established volume loss measure.”
The authors noted that “it is possible that disease-related reduction in signal amplitude has minimal impact on temporal correlations. fALFF is correlated with local functional connectivity in healthy controls; however, it remains to be tested whether fALFF abnormalities in central hubs such as the hippocampus are associated with long range network dysfunction in TLE.”
Reyes A, Thesen T, Wang X, et al. Resting-state functional MRI distinguishes temporal lobe epilepsy subtypes. Epilepsia. 2016; doi:10.1111/epi.13456.