To assess the long-term effects of temporal lobe epilepsy surgery on verbal memory.Methods:
We assessed verbal memory performance as measured by a verbal learning test (“15 Words Test,” a Dutch adaptation of Rey's Auditory Verbal Learning Test) before surgery and at three specific times after surgery: 6 months, 2 years, and 6 years in 85 patients (34 left temporal lobe [LTL] vs. 51 right temporal lobe [RTL]). An amygdalo-hippocampectomy and a neocortical temporal resection between 2.5 and 8 cm were carried out in all patients.Results:
LTL patients showed an ongoing memory decline for consolidation and acquisition of verbal material (both 2/3 SDs) for up to 2 years after surgery. RTL patients at first showed a gain in both memory acquisition and consolidation, which vanished in the long term. Breaking the group up into a mesiotemporal (MTS) group and a non-MTS group showed clear differences. The group with pure MTS showed an overall lower verbal memory performance than the group without pure MTS, in the LTL group more pronounced than in the RTL group. After surgery, both pathology groups showed an ongoing decline for up to 2 years, but the degree of decline was greater for the LTL patients with MTS compared with the non-MTS group. Becoming and remaining seizure-free after surgery does not result in a better performance in the long term. Predictors of postoperative verbal memory performance at 6 years after surgery were side of surgery, preoperative memory score, and age.Conclusions:
The results provide evidence for a dynamic decline of verbal memory functions up to 2 years after left temporal lobectomy, which then levels off.