Abstracts

Rationale: Surgery is increasingly used as treatment for refractory focal epilepsy. Only a few studies have examined the development of psychogenic nonepileptic seizures (PNES) after epilepsy surgery. Our aim was to identify the factors associated with occurrence of PNES after adult epilepsy surgery. Methods: We identified patients diagnosed with PNES from the long-term outcome data of 805 patients who underwent epilepsy surgery between 1990 and 2012, at the National Hospital for Neurology and Neurosurgery (NHNN), London, UK. The diagnosis was clinical in all cases, further confirmed by video-EEG monitoring in doubtful cases. Multivariate analysis was performed comparing the characteristics of the PNES patients to the other epilepsy surgery patients. Patients' gender, the patients' age and duration of epilepsy at the time the surgery was performed, pre-surgical psychiatric co-morbidities including depression and seizure outcome after surgery were used as covariates. Results: The frequency of patients developing PNES after epilepsy surgery in our series was 3.23 %. Specifically, twenty six patients (20 women, 76.9 %) were identified and recruited in the study, with 20 anterior temporal resections, 2 temporal lesionectomies, 3 extratemporal lesionectomies and 1 multiple subpial transaction were performed (one patient had undergone anterior temporal resection twice). Patients had undergone surgery at a median age of 35 y (range 18-50 y) and there was a wide interval between the date of surgery and development of PNES (6 weeks - 10 years). The frequency of PNES was also variable, and the semiology differed from the occasional epileptic seizures in most patients. Fourteen of the PNES patients had comorbid depression or psychosis, whereas in the remaining 12 patients, PNES developed independently of other psychiatric disorders. Statistical analysis revealed that female gender and the pre-surgical presence of depression were significantly associated with PNES. After multivariate analysis, with all the aforementioned parameters in the model, the female gender was the only parameter independently associated with dissociative seizures (p=0.025, OR=2.89). Conclusions: PNES can occur after epilepsy surgery and do not appear to be related to postsurgical seizure outcome. In patients who continue to have epileptic seizures, the semiology of the PNES tends to differ from that of their epileptic seizures. Female patients are at greater risk of developing PNES after epilepsy surgery.