A longitudinal study of cognitive changes after surgical treatment for epilepsy

Sammanfattning: Epilepsy surgery is a valuable therapeutic option for some patients with pharmaco-resistant partial epilepsy, but resection of cortical tissue carries a risk of creating or worsening a dysfunction. Therefore pre-and postoperative levels of cognitive function are systematically monitored in epilepsy surgery programs. One aim of the present neuropsychological study was to describe general cognitive function and memory preoperatively, and change two years postoperatively, in adults in the Göteborg epilepsy surgery series. For this purpose data were analysed for 70 consecutive patients in Study I. In study II the purpose was to explore the hypothesis that analysis with appropriate methods would yield more knowledge about the individual variability separately from group patterns in a more homogeneous group of 54 temporal lobectomy patients. In study III the long-term change (10 years) after surgery was studied in a subgroup of 25 temporal lobectomy patients. In study IV the purpose was to investigate cognitive changes across time in 36 patients with pharmaco-resistant partial epilepsy who had not been operated and to explore the hypothesis that a cognitive decline over time would be disclosed. A control group of 30 neurologically healthy persons was matched to the patients and 25 of these participated in a follow-up. Results in Study I showed that preoperatively the general cognitive level (Full Scale IQ and Impairment Index) was lower in patients than in controls (p<0.01). Performance in aspects of verbal and visual memory was more impaired in the temporal lobe subgroups than in controls (p<0.01). The impairment was congruent with the lateralisation of seizure origin (verbal in the speech-dominant and visual in the non-dominant group). Postoperatively a slight increment in general intellectual status was found (p<0.01) for the total patient group and for the frontal lobe group (p<0.05). In Study II a significant (p<0.05) postoperative impairment in verbal associative memory was found in the left temporal lobectomy group. Individual heterogeneity (declines as well as improvements) unexplained by group patterns was significant in both verbal and visuospatial memory variables and was measurable with the non-parametric relative rank variance parameter. In Study III cognitive stability was the main finding at long-term follow-up together with patterns of residual decrement and increment at an individual level in 28% versus 16% of the patients. In Study IV, deterioration was found in the non-operated patients in delayed recall of verbal associative memory (p<0.05) as well as adverse change in aspects of general cognition (p<0.01) across time.Cognitive stability was the main postoperative result at group level together with a significant postoperative impairment in verbal associative/episodic memory after left temporal lobectomy at the two year follow-up. There were no long-term changes in cognition at group level. Impairment in verbal associative/episodic memory was also found in the group of non-operated patients at follow-up. However, with comprehensive evaluation methods important patterns of change with decrements as well as increments at an individual level could be discerned. Factors relevant for the interpretation of this heterogeneity, such as practice effects, regression toward the median and reliability issues related to memory tests, are discussed. Other aspects may have to be studied in larger series. At present prediction of memory outcome after epilepsy surgery can to some extent be made at group level, but not at an individual level.