Abstracts

Rationale: Epilepsy patients report stress as a trigger for seizures. Animal models of epilepsy provide evidence for the involvement of stress in the development of epilepsy and have shown stress to be a seizure precipitant. However, the role of stress in human epilepsy is poorly understood. Our objective was to assess the endocrine response to an acute psychosocial stress in left temporal lobe epilepsy (LTLE). Methods: Included in the study were 23 LTLE patients who either believe (+S; n=16) or do not believe (-S; n=7) that stress is an important factor in their seizure control and 17 healthy subjects (HC) matched for age and sex. Subjects underwent a stress challenge similar to the Montreal Imaging Stress Task (Dedovic et al, 2005) designed to produce moderate increases in the stress hormone cortisol (CORT). The stress challenge was performed as part of an fMRI scan session and consisted of a task in which subjects performed difficult subtraction problems and were given negative feedback regardless of their actual performance. CORT was assessed at 30 and 15 min before and at 0, 15, 30, 45 and 60 min after scanning (t=1-7). 2-sample t-tests assessed group differences in CORT at each of the 7 time points, with specific interest in t=3 which is the time point directly following the stress challenge. Due to the possible interplay between stress and seizures, LTLE patients were also analyzed as those who are seizure free (i.e., no reported seizures in past 3 months; -sz) and those who are not (+sz). Effect size and power calculations for CORT at t=3 were performed between +sz and -sz groups. Results: There were no significant differences in CORT levels between LTLE +S and -S groups or between HC and either +S or -S groups (all p>.1) indicating that chronic stress may have less effect on CORT levels than previously thought. Analysis based on seizure freedom revealed no significant differences in CORT levels between LTLE +sz and -sz groups or between HC and either +sz or -sz groups (all p>.07). However, LTLE +sz showed a spike in CORT at t=3 compared to -sz (p=.13) and HC (p=.1), while similar levels (p=.69) were observed in HC and -sz (Fig. 1). There was a medium-large effect size of CORT between +sz and -sz at t=3 (Cohen's d=.65); with larger sample sizes of 21 per group and level of significance set at p=.05, we would have 81% power to detect group differences in post-stress challenge CORT. Conclusions: LTLE +sz show increased response to stress compared to HC and -sz groups, while HC and -sz show similar patterns of CORT throughout. The elevated stress response in +sz patients may be a factor contributing to or resulting from the continued seizures observed in this group. Given that temporal lobe regions are involved in the endocrine stress response, seizure activity may have an adverse modulatory effect. This is the first study of its kind to investigate the relationship between the endocrine stress response and human epilepsy.