Evaluation of limbic microstructural abnormalities in temporal lobe epilepsy: A neurite orientation distribution and density imaging study.

Objective: Widespread structural pathology in the limbic system is a hallmark of temporal lobe epilepsy (TLE). In this work, we sought to describe a comprehensive readout of limbic abnormalities in TLE using neurite orientation distribution and density imaging (NODDI).

Methods: This is a retrospective study of patients with drug-resistant TLE and healthy controls who underwent research magnetic resonance imaging. We estimated the degree of deviation of the NODDI parameters neurite density index (NDI) and orientation dispersion index (ODI) from healthy controls in limbic regions in the form of univariate z-scores. We calculated a multivariate deviation score combining both NDI and ODI (Mahalanobis distance). A summary score representing the overall level of deviation across limbic regions was then computed using the sum of regional deviation scores. We next assessed the diagnostic performance of summary scores in lateralizing TLE as well as associations with neuropsychological deficits and 12-month surgical outcome.

Results: The Mahalanobis distance revealed unique patterns of abnormalities between TLE participants (n = 74) and controls (n = 42), with only four of 18 (22%) areas displaying overlapping univariate and multivariate deviations. The multivariate summary score achieved the highest diagnostic accuracy in clinical lateralization of nonlesional TLE (area under the curve [AUC] = .95, 95% confidence interval [CI] = .77-1). Among surgical patients (n = 30), summary scores corresponding to the hemisphere ipsilateral and contralateral to surgery were predictive of seizure freedom at 12 months (AUC = .84, 95% CI = .76-.93).

Significance: We demonstrate unique patterns of abnormalities in neurite density and coherence in limbic microstructure in TLE. A summary score accounting for deviations in both neurite density and coherence achieved high diagnostic accuracy in clinical lateralization of TLE and was associated with surgical outcomes, warranting further study as a putative biomarker in TLE to be used alongside clinical data.