Abstracts

It has been reported that secondarily generalized tonic-clonic seizures (GTCS) become more frequent after ATL. We tried to replicate these findings in a larger patient sample, further investigate postoperative changes in seizure severity, and evaluate risk factors for postoperative occurrence of GTCS.
All clinical data was maintained prospectively in an electronic database. Seizure type and frequency were registered for patients before and after ATL for refractory epilepsy. The following variables were assessed to determine if they influenced likelihood of occurrence of GTCS after ATL: age at time of surgery, gender, age at seizure onset, history of febrile seizures, latency in years between risk factor for epilepsy and onset of seizures, contralateral memory function as measured by the Wada test, full scale IQ, preop seizure frequency, preop seizure type, and presence or absence of preoperative GTCS. Non-parametric analyses and parametric statistics were used as appropriate. This project was approved by the Jefferson IRB.
Of 464 patients who underwent ATL between 1986 and 2001, 146 patients had one or more postoperative complex partial seizures (CPS) or GTCS. Among the 146 patients who experienced seizure recurrence, the overall prevalence of GTCS did not change. 68 patients (46.58%) had preop GTCS, while 73 patients (50%) had postop GTCS (p = 0.74). However, seizure type did change in individual patients; only 86 patients (58.90%) had identical seizure types before and after surgery. Of 78 patients with only complex partial seizures before surgery, 27 (34.62%) developed GTCS after surgery. Of 68 patients who had GTCS before surgery, 22 (32.35%) had only complex partial seizures after surgery. GTCS comprised a greater proportion of the total number of seizures before ATL (18.08%), than after surgery (35.89%) (dependent samples t-test, p[lt]0.01). Preop seizure type was the best predictor of postop seizure type, and the presence of preop GTCS and a greater preop GTCS frequency were the only predictors of postop GTCS occurrence; no other risk factors examined influenced postop GTCS occurrence.
Seizure severity may change after ATL, both for the better and the worse in individual patients.While overall GTCS prevalence does not increase, there is an increase in the proportion of GTCS after surgery. This could reflect greater efficacy in reducing CPS than GTCS by ATL, but also suggests that intrinsic mechanisms for regulating seizure propagation are altered by surgery. Both local and distant circuits regulating excitability may be affected.
[Supported by: Dr. Sperling is supported in part by the NIH.]