The effect of epilepsy surgery on tonic-clonic seizures

Objective: Epilepsy surgery outcomes tend to be judged by the percentage in seizure reduction without considering the effect on specific seizure types, particularly tonic-clonic seizures, which produce the greatest morbidity and mortality. We assess how often focal to bilateral tonic-clonic seizures (BTCS) stop and how often they appear de novo after epilepsy surgery.

Methods: Analysis of a prospectively maintained epilepsy surgery database between 1986 and 2022 that characterizes the burden of BTCS after resective epilepsy surgery. Patients were stratified according to presence or absence of preoperative BTCS and whether these were active (defined as ≥1 BTCS/year prior to surgery) or remote.

Results: A total of 804 patients were followed for a median of 7 years (interquartile range [IQR] = 3-13 years) after epilepsy surgery, most being temporal lobe resections (91%, 95% confidence interval [CI] = 89-93%). At last visit, 72% of patients (95% CI = 69-75%) were seizure-free for 1 year or more. Of 521 patients with preoperative BTCS, 300 (58%, 95% CI = 53%-61%) no longer had them after surgery. BTCS recurred in 221 patients, but 128 of them (58%, 95% CI = 51%-64%) had no BTCS in the last year of follow-up. Those patients who continued to experience BTCS after surgery had a median reduction of 92% in yearly BTCS frequency (IQR = 65%-98%, p < .001). Of 283 patients with no preoperative BTCS, 17 developed de novo BTCS (6%, 95% CI = 4%-9%), with a median of 2 BTCS during the entire follow-up period. Forty-seven percent (95% CI = 42%-53%) of patients without preoperative BTCS became seizure-free after surgery, compared with 33% (95% CI = 29-37, p < .001) of patients with preoperative BTCS.

Significance: Epilepsy surgery markedly reduces or eliminates BTCS, which should have a potential positive impact on morbidity and mortality. This favors offering surgery even if the chance of seizure freedom is not high and calls for a new surgical outcome scale to factor in seizure severity reduction.