Factors influencing the adequacy of determining hemispheric language lateralization in presurgical epilepsy patients using functional transcranial Doppler sonography (fTCD)

As the adequacy of determining hemispheric language lateralization (HLL) is of special importance for the planning of epilepsy surgery, this study aimed to identify predictive factors for receiving inconclusive HLL results using functional transcranial Doppler sonography (fTCD). Data from 495 epilepsy patients who received fTCD in a standardized fashion was analyzed retrospectively. HLL was left-sided in 324 patients (65.5 %), right-sided in 76 (15.4 %), and inconclusive in 95 (19.2 %). Univariate logistic regression analyses revealed significant positive associations between inconclusive HLL results and a multiregional localization of epilepsy. Significant negative associations with higher educational qualification, more years of education, and better letter verbal fluency were found. In multiple logistic regression analyses, a multiregional localization of epilepsy (OR = 2.74, p <0.001) and years of education (OR = 0.86, p < 0.001) remained independent predictors. A cut-off value of 10.77 years of education determined by discriminant function analyses is provided. Our findings indicate that the adequacy of determining HLL using fTCD is highly dependent on the extension of the epileptogenic lesion and the patients' years of education. We therefore recommend not to use the same paradigm for all patients, but to adapt the selection of adequate test materials to their cognitive abilities.