Long-Term Cognitive Outcomes After Epilepsy Surgery in Adults

Abstract

The literature on the long-term (>5 years) changes in cognitive function in people who undergo epilepsy surgery is small and currently limited to series who have undergone temporal lobe resections. This reflects both pragmatic and cultural factors. Longitudinal studies suggest that the majority of epilepsy surgery candidates have stable memory functions at assessments conducted more than 5 years after surgery, with scores comparable to those they obtained 12–24 months after the operation. There is a subset of patients in whom ongoing seizures are associated with progressive memory impairment. These individual patterns of change are obscured in group analyses. Left temporal lobe resections are consistently identified as a risk factor for progressive deterioration in verbal memory decline, particularly in those with good preoperative function. However, “floor effects” on the standardized tests used to assess cognitive function, evident prior to surgery or soon afterwards, may mask long-term deterioration in a considerably larger proportion of these patients than the literature currently suggests. Some improvements in verbal memory function have been reported at long-term follow-up in patients who have undergone right temporal lobe resections. More research is urgently needed to identify those most at risk of long-term deterioration in memory function following a temporal lobe resection and to examine the long-term trajectories of cognitive function following extratemporal surgeries.

Conflicts of Interest

The author has no conflicts of interest to declare.

Appendix. Summary of Study Characteristics and Results from Long-Term Cognitive Outcome Series

Authors	Participants	Follow-up	Neuropsychological Tests	Analyses	Results
Andersson - Roswall et al. (2012) [7] Sweden	N = 51 23 DTL 28 NDTL	2 years 10 years	The Claeson–Dahl Learning and Retention Test (CD) – List learning task Cronholm–Molander Memory Test (CM) (word pair associations)	Reliable change indices to determine significant change	Most patients had stable verbal memory postoperatively. Some patients showed partial recovery, especially in the NDTL group. Fewer patients had reliable declines at 10 years than at 2 years. The only risk factor for decline both short- and long-term was DTL resection
Baxendale et al. (2012) [8] UK	N = 70 33 LTL 37 RTL	3 months 1 year >5 years (mean 9.1 years; range 5–17 years)	Wechsler Adult Intelligence Scales Adult Memory & Information Processing Battery Verbal Learning Visual Learning	Group changes over time Reliable change indices to determine significant change	The majority of patients had stable memory function across the assessments. However, many were functioning below the 15th percentile on the test norms preoperatively with little capacity for further decline. Progressive decline in cognitive function was associated with poor postoperative seizure control
Andersson - Roswall et al. (2010) [6] Sweden	N = 51 23 DTL 28 NDTL	2 years 10 years	The Claeson–Dahl Learning and Retention Test (CD)  List learning task  Visual memory task Rey Osterreith Complex Figure Task Cronholm–Molander Memory Test (CM) (word pair associations)	Group analyses	The DTL group had declined in verbal memory at the 10-year follow-up compared to the NDTL group and to the controls. However, this decline was detected already 2 years postoperatively, with no further decline from 2 to 10 years
Alpherts et al. (2006) [5] Netherlands	34 LTL 54 RTL (SAH)	6 months 2 years 6 years	Wechsler Adult Intelligence Scales Rey Auditory Verbal Learning Test (Dutch Version)	Group analyses	LTL patients demonstrated a progressive decline in consolidation and acquisition of verbal material for up to 2 years after surgery. This decline is greater in patients with mesial temporal sclerosis. The RTL patients demonstrated an initial gain in both memory acquisition and consolidation, which vanished in the long-term Predictors of postoperative verbal memory performance at 6 years after surgery were side of surgery, preoperative memory score and older age. Memory outcome was not related to postoperative seizure control
Engman et al. (2006) [9] Sweden	N = 25 10 DTL 15 NDTL 25 healthy controls	2 years 10 years	Wechsler Adult Intelligence Scales Cronholm–Molander Memory Test (CM) – word pair associations Rey Osterreith Complex Figure Test	Group analyses	At the group level, there was a significant increment across time in IQ, partly due to practice effects. This was not seen in the memory scores. The analysis at the individual level of change from baseline to 2 years suggested a decline in memory scores which returned towards baseline level at the 10-year follow-up. These findings suggest that some deterioration in memory function recorded at the 2-year follow-up may not be stable in the long-term
Rausch et al. (2003) [11] USA	N = 21 LTL 23 RTL N = 8 Non surgical, epilepsy controls	1 year >9 year (mean 12.1, range 9.1–19 years)	Wechsler Adult Intelligence Scales Wechsler Memory Scales  Paired associate learning  Prose recall  Visual reproduction	Group analyses	Patients with LTL surgery showed selective early decreases in verbal memory. At the long-term follow-up, further decreases in verbal memory and visual memory scores were seen for all patient groups. Non- memory scores remained stable over time. LTL surgery and initial high scores were predictors of verbal memory decreases seen at the early follow-up. Late memory declines were predicted by higher 1-year scores. LTL surgery was an additional predictor of late verbal memory decline
Helmstaedter et al. (2003) [10] Germany	N = 147 surgical patients 72 LTL 75 RTL 102 non surgical, epilepsy controls	1 year 2–10 years (median = 49 months)	Verbal learning memory test (German version) Figural memory test Letter cancellation task Phonetic word fluency task Vocabulary test	Group analyses Reliable change indices	Fifty percent of the medically treated and 60 % of the surgical patients showed significant memory decline at long-term follow-up with no significant change in non-memory functions. Surgery accelerated the decline seen in the medically treated group and exceeded it when surgery was performed on the left, or if seizures continued postoperatively. Seizure-free surgical patients showed recovery of non-memory functions at 1 year after surgery and of memory functions at long-term follow-up. Multiple regression indicated retest interval, seizure control, and mental reserve capacity as predictors of performance changes