Abstracts

Rationale: Mesial temporal lobe epilepsy (MTLE) is the most common form of human epilepsy. A reliable estimate of the side of epileptogenic zone is critical to decision-making in surgery of patients with refractory MTLE. The decision to proceed with the temporal lobectomy depends on the concordance between the side of mesial temporal sclerosis (MTS) demonstrated by MRI and the electrophysiological recordings. Despite the recent advances in diagnostic technologies, there is no consensus on which diagnostic tests are necessary in unilateral MTLE. Although some authors consider the role of ictal EEG irreplaceable, other series support that a concordant outpatient EEG evaluation in patients with MTLE and unilateral MTS would obviate the need for ictal EEG recordings. To access the diagnostic value of diagnostic tool used in presurgical evaluation of MTLE patients the likelihood ratios (LRs) and 95% credible intervals (CrIs) were estimated by using a Bayesian hierarchical model. Methods: Bayesian methodologies were applied to this study. One-hundred and eighty five patients with refractory MTLE were prospectively included. We used surface, foramen ovale, and depth ictal EEG as a gold standard. We calculated the sensitivity, specificity, likelihood ratio, and post-test probability for patients with left and right MTS revealed by MRI. Results: We found that in patients with left MTS the sensitivity was 0.94, the specificity was 0.93, the likelihood ratio was 14 (95% CI 6.28 to 30.0), and the post-test probability that the seizure originate in the left TL if the MRI reveal left MTS is 94% (95% CI = 88% to 97%). In patients with right MTS the sensitivity was 0.93, the specificity was 0.94, the likelihood ratio was 15 (95% CI 7.0 to 33.0), and the post-test probability that the seizure originate in the right TL if the MRI reveal right MTS is 93% (95% CI = 86% to 97%). If we analyze the likelihood ratio in those patients with unilateral interictal spikes (UIS), the likelihood ratio increases to 56 (95% CI 8.0 to 389.0) in patients with left MTS, with a post-test probability of 99% (95% CI = 91% to 100%). In patients with right MTS and UIS the likelihood ratio increases to 37 (95% CI 8.21 to 76.0), with post-test probability of 97% (95% CI = 87% to 99%). Conclusions: Although the concepts of sensitivity and specificity are critically important to those who work in the clinical laboratory, for clinicians caring for patients the more important issue is the probability that a given test indicates the disease. In the setting of MTLE, the epileptologists need to know the probability that the seizures originate in the side indicated by RMI. In a sample of patients with refractory MTLE, we demonstrate that the probability that the seizures originate ipsilateral to the side of MTS is from 93-94% (95% CI 86% to 97%). If the interictal spikes are ipsilateral to the side of unilateral MTS this probability increases to 97-99% (95% CI 87% to 99.0%).