Tonic seizures: Their significance for lateralization and frequency in different focal epileptic syndromes

Purpose: To determine whether the clinical features of tonic seizures (TSZ) are useful for lateralization of epileptic syndromes and the differential diagnosis of focal epileptic syndromes. Methods: From a group of 481 patients, 123 patients with TSZ (44 females; m ean age, 22.9 years; mean age at onset, 7 years; mean duration of epilepsy, 16 years) were selected. A total of 1595 epileptic seizures, documented du ring video-electroencephalographic monitoring, were analyzed. Patients who had had surgery for epilepsy previously were excluded. Seizures were classi fied using a semiological seizure classification. Epilepsy syndromes were c lassified using all test data (electroencephalography, magnetic resonance i maging, computed tomography, positron emission tomography, and single-photo n emission tomography). Data were compared using X-2 analysis or the Fisher exact test. Results: More patients with TSZ had extratemporal than temporal lobe epilep sies (79% vs. 1.7%; p < 0.0001) among those with an epilepsy localized to o ne lobe (n = 306). In the 123 patients, TSZ were part of 170 different seiz ure evolutions. Seizure evolutions began with TSZ as the first seizure type more often in patients with frontal lobe epilepsy (FLE) compared with pati ents with parieto-occipital lobe epilepsy (POLE) (40% in POLE vs. 67% in FL E; p < 0.05). In contrast, TSZ in POLE were more likely to be preceded by a uras (50% in POLE vs. 26% in FLE; p < 0.05). TSZ were bilateral in 129 (76% ) and unilateral in 41 (24%) seizure evolutions. Unilateral TSZ correctly l ateralized the epilepsy syndrome to the contralateral hemisphere. Conclusion: Analysis of seizure semiology and evolution in patients with TS Z is helpful for differentiating between focal epilepsies of temporal, fron tal, and parieto-occipital origin. Unilateral TSZ provide useful informatio n for the lateralization of the epileptic syndrome.