Unitemporal vs bitemporal hypometabolism in mesial temporal lobe epilepsy

Background: Patients with mesial temporal lobe epilepsy (TLE) often show bilateral temporal hypometabolism (BTH), but the nature of this finding has not been well established. Objective: To compare the clinical characteristics between unitemporal hypometabolism (UTH) and BTH patients in mesial TLE. Design: Cross-sectional study. Setting: Epilepsy center at university hospital in Seoul, Korea. Patients: We enrolled 95 patients with mesial TLE, 87 of whom had subsequently undergone surgery. Seizures, interictal and ictal electroencephalography (EEG), brain magnetic resonance imaging, Wada test, and neuropsychological test results were reviewed. ¹⁸F-fluorodeoxyglucose positron emission tomography scans were interpreted visually. Patients were divided into 2 groups: UTH and BTH. Results: There were 59 UTH patients and 36 BTH patients. Semiologic analysis showed that UTH patients had higher frequencies of aura and unilateral dystonic posturing, whereas BTH patients had higher frequencies of a nonlateralized bilateral ictal EEG pattern and bilateral interictal spikes. Moreover, BTH patients had more frequent symmetric Wada memory scores and white matter changes in the bilateral temporal lobes on brain magnetic resonance imaging than UTH patients. All UTH patients with bilateral TLE on scalp EEG showed unilateral seizure onset on intracranial EEG. Conclusions: The characteristic clinical findings of mesial TLE with BTH were a more frequent nonlateralized ictal EEG pattern, bitemporal interictal spikes, symmetric Wada memory score, and the anterior temporal white matter changes, and less frequent aura and unilateral dystonic posturing. Surgical outcomes were similar and good in both groups, although surgery could not be performed in 8 BTH patients (22%).