Chronic epilepsy and cognition: A longitudinal study in temporal lobe epilepsy

Volumetric Magnetic Resonance Imaging of Functionally Relevant Structural Alterations in Chronic Epilepsy after Pilocarpine-induced Status Epilepticus in Rats

PURPOSE

After pilocarpine-induced epilepsy in rats, volumetric magnetic resonance imaging (MRI) reveals significant morphologic changes in functionally relevant structures of the brain. To relate structural changes to functional alteration, we studied the correlation of regional brain atrophy (e.g., of the hippocampus) with lesion-induced learning deficits in the Morris water maze.

METHODS

MRI experiments were performed on an MR scanner at 4.7 Tesla. For volumetric analysis, various cerebral structures were segmented in horizontal and coronal T(2)-weighted MR images. Before the MRI investigations, animals were trained for 10 days in a Morris water maze.

RESULTS

Volumetric MRI revealed a significant loss in hippocampal size in both the dorsal and ventral parts, correlated with an increase in ventricular size. Furthermore, significant losses were found in the relative size of thalamus, putamen, cortex, and the combined areas of perirhinal, entorhinal, and piriform cortices adjacent to the hippocampus. A significant correlation of learning performance in the Morris water maze with the relative hippocampal area and not with other areas tested was observed in pilocarpine-treated animals.

CONCLUSIONS

The data provide a quantitative analysis of functionally relevant structural alterations in rats with chronic epilepsy. Water maze performance of pilocarpine-treated animals correlates with the degree of hippocampal but not with the degree of cortical damage, demonstrating the potential of this method for the investigation of cognitive impairments in relation to cerebral changes. In addition, the data point to an important role of even the residual hippocampus in memory formation.

Long-term seizure outcomes following epilepsy surgery: a systematic review and meta-analysis

Assessment of long-term outcomes is essential in brain surgery for epilepsy, which is an irreversible intervention for a chronic condition. Excellent short-term results of resective epilepsy surgery have been established, but less is known about long-term outcomes. We performed a systematic review and meta-analysis of the evidence on this topic. To provide evidence-based estimates of long-term results of various types of epilepsy surgery and to identify sources of variation in results of published studies, we searched Medline, Index Medicus, the Cochrane database, bibliographies of reviews, original articles and book chapters to identify articles published since 1991 that contained > or =20 patients of any age, undergoing resective or non-resective epilepsy surgery, and followed for a mean/median of > or =5 years. Two reviewers independently assessed study eligibility and extracted data, resolving disagreements through discussion. Seventy-six articles fulfilled our eligibility criteria, of which 71 reported on resective surgery (93%) and five (7%) on non-resective surgery. There were no randomized trials and only six studies had a control group. Some articles contributed more than one study, yielding 83 studies of which 78 dealt with resective surgery and five with non-resective surgery. Forty studies (51%) of resective surgery referred to temporal lobe surgery, 25 (32%) to grouped temporal and extratemporal surgery, seven (9%) to frontal surgery, two (3%) to grouped extratemporal surgery, two (3%) to hemispherectomy, and one (1%) each to parietal and occipital surgery. In the non-resective category, three studies reported outcomes after callosotomy and two after multiple subpial transections. The median proportion of long-term seizure-free patients was 66% with temporal lobe resections, 46% with occipital and parietal resections, and 27% with frontal lobe resections. In the long term, only 35% of patients with callosotomy were free of most disabling seizures, and 16% with multiple subpial transections remained free of all seizures. The year of operation, duration of follow-up and outcome classification system were most strongly associated with outcomes. Almost all long-term outcome studies describe patient cohorts without controls. Although there is substantial variation in outcome definition and methodology among the studies, consistent patterns of results emerge for various surgical interventions after adjusting for sources of heterogeneity. The long-term (> or =5 years) seizure free rate following temporal lobe resective surgery was similar to that reported in short-term controlled studies. On the other hand, long-term seizure freedom was consistently lower after extratemporal surgery and palliative procedures.

ApoE epsilon4 allele and disease duration affect verbal learning in mild temporal lobe epilepsy

PURPOSE

To clarify the possible role of other factors including the ApoE epsilon4 allele for memory decline in temporal lobe epilepsy (TLE).

METHODS

We conducted a neuropsychological and molecular study in 138 consecutive patients (78 female patients; mean age, 50.2 years, SD +/- 17.9; range, 14 to 87 years) with mild nonlesional TLE, who rarely or never had seizures at long-term follow-up. The mean age at seizure onset was 33.0 years (SD, +/-21.7), and the mean duration of epilepsy was 17.1 years (SD, +/-15.7).

RESULTS

Thirty-four (25%) of 138 patients had test scores indicating verbal learning deficit (VLD). The presence of an ApoE epsilon4 allele was associated with an increased risk of VLD (OR, 4.18; 95% CI, 1.66-10.55). The effect of the ApoE genotype was independent of both the age at epilepsy onset and disease duration as well as of a low educational level, which were separately associated with VLD (p values = 0.045, 0.001, and 0.001, respectively). A significant linear trend (p = 0.005) was seen in the relation between disease duration and cognitive impairment, with the highest risk being in patients with an epilepsy duration > or =25.5 years (OR, 7.06; 95% CI, 1.67-29.85), especially if they carried the epsilon4 allele (OR, 32.29; 95% CI, 5.23-195.72).

CONCLUSIONS

These results provide evidence for an alteration in cognitive performance as a function of the presence of the ApoE epsilon4 allele and point to the critical role of disease duration itself for cognitive impairment in TLE.

Whole-brain voxel-based statistical analysis of gray matter and white matter in temporal lobe epilepsy

Volumetric MRI studies based on manual labeling of selected anatomical structures have provided in vivo evidence that brain abnormalities associated with temporal lobe epilepsy (TLE) extend beyond the hippocampus. Voxel-based morphometry (VBM) is a fully automated image analysis technique allowing identification of regional differences in gray matter (GM) and white matter (WM) between groups of subjects without a prior region of interest. The purpose of this study was to determine whole-brain GM and WM changes in TLE and to investigate the relationship between these abnormalities and clinical parameters. We studied 85 patients with pharmacologically intractable TLE and unilateral hippocampal atrophy and 47 age- and sex-matched healthy control subjects. The seizure focus was right sided in 40 patients and left sided in 45. Student's t test statistical maps of differences between patients' and controls' GM and WM concentrations were obtained using a general linear model. A further regression against duration of epilepsy, age of onset, presence of febrile convulsions, and secondary generalized seizures was performed with the TLE population. Voxel-based morphometry revealed that GM pathology in TLE extends beyond the hippocampus involving other limbic areas such as the cingulum and the thalamus, as well as extralimbic areas, particularly the frontal lobe. White matter reduction was found only ipsilateral to the seizure focus, including the temporopolar, entorhinal, and perirhinal areas. This pattern of structural changes is suggestive of disconnection involving preferentially frontolimbic pathways in patients with pharmacologically intractable TLE.

Intelligence functions disorders in patients with complex partial epilepsy

OBJECTIVES: To compare the performance of patients with complex partial epilepsy with the normal controls in the subtests of an instrument used to assess intelligence function. METHOD: Fifty epileptic patients, whose ages ranged from 19 to 49 years and 20 normal controls without any neuropsychiatric disorders. The Wechsler-Bellevue adult intelligence test was applied in groups, epileptic patients and control subjects. This test is composed of several subtests that assess specific cognitive functions. A statistical analysis was performed using non-parametric tests. RESULTS: All the Wechsler-Bellevue subtests revealed that the intelligence functions of the patients were significantly inferior to that of the controls (p<0.05). This performance was supported by the patient's complaints in relation to their cognitive performance. CONCLUSION: Patients with complex partial epilepsy presented poorer results in the intelligence test when compared with individuals without neuropsychiatric disorders.

Memory in Patients with Drug-responsive Mesial Temporal Lobe Epilepsy and Hippocampal Sclerosis

PURPOSE

Mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) is the most common of the antiepileptic drug (AED)-resistant seizure syndromes that are remediable mostly with surgery, although a small group of patients have benign prognosis with fewer seizures. Material-specific memory impairment is an important feature in these patients and may be related to both the structural abnormality and the frequent seizures. In this study, we investigated the relation between memory deficit and HS by taking seizure frequency into account.

METHODS

The patients were evaluated according to a standard protocol and divided into two groups, considering their response to AEDs: the good-responder group (GRg, n = 18) and the pharmacoresistant group (PRg, n = 95). They were administered a neuropsychological test battery that included verbal and nonverbal memory tests, compared with each other and with a normal control group (n = 29). The responder group was evaluated by the same battery once again (mean, 23 months; SD, 8.25; range, 14-38 months).

RESULTS

Both GR and PR patient groups had poorer memory than the normal controls in all memory tests (p < 0.05). However, the comparison of GRg with PRg revealed that only the digit-span test was significantly worse in PRg (p = 0.0061), and no difference was found in any other memory scores. The reevaluation of the GRg showed no significant difference between the first and second evaluation.

CONCLUSIONS

We concluded that the memory impairment in patients with MTLE-HS was permanent and might be related to the direct effect of HS itself. Therefore patients with good response to AEDs can be used as a model for investigating the memory problems in patients with MTLE-HS.

Prescribing antiepileptic drugs: should patients be switched on the basis of cost?

To assess the costs of switching from one antiepileptic drug (AED) to another, all associated direct and indirect costs, not only drug acquisition costs, must be considered. The perspective of the healthcare system evaluated in cost-effectiveness analysis is of crucial importance. Multiple clinical factors can influence clinical decisions regarding switching AEDs. The economic cost of poorly controlled epilepsy is enormous and the most cost-effective intervention is an AED that provides total seizure control. Cost-minimisation studies have evaluated costs associated with various medications. If only efficacy and adverse events were considered, then the 'older' AEDs were generally more cost effective than the 'newer' AEDs. Most studies only examine very specific clinical situations and are not suitable for establishing general clinical recommendations. The pharmacoeconomics of AED choice is highly country specific. While switching to generic formulations is, in general, cost effective, some changes may be detrimental and more costly than remaining on the trade name preparation. For example, as a result of differences in bioavailability and possible loss of seizure control, changing patients to generic phenytoin and carbamazepine can be problematic. Fosphenytoin may only be cost effective in certain clinical situations compared with intravenous phenytoin. Seizure control should not be sacrificed on the basis of costs alone, as the major endpoint in treating epilepsy with AEDs is seizure control without adverse effects. Switching AEDs in clinical practice still depends on the individual clinical situation and choosing AED therapy solely on the basis of initial acquisition costs is unlikely to be cost effective in the long-term care of patients with epilepsy.

Verbal memory decline and adverse effects on cognition in adult patients with pharmacoresistant partial epilepsy: a longitudinal controlled study of 36 patients

The aim of this study was to delineate possible longitudinal cognitive changes in adult patients with a long history of pharmacoresistant partial epilepsy. Thirty-six patients and thirty healthy controls were investigated at baseline. A reassessment was conducted, with median test intervals of 4.8 years for the patients and 3.1 years for controls. A standardized battery was used for assessment of general cognitive level and memory. At baseline, patients performed at a significantly lower level on general cognition, immediate recall of pairs of associated words, and retention of learned words and visuospatial stimuli, compared with controls. Analyses of change over time in the patients disclosed significant verbal memory decline in retention of pairs of associated words. Group comparisons of change over time revealed adverse effects in the performance aspect of general cognition on the patients. Also, group comparisons indicated impaired performance across time for the patients in retention of pairs of associated words and retention of visuospatial stimuli. The adverse effect on memory and general cognition in this patient group over the period was clear-cut when compared with the longitudinal changes in an adequate control group.

Qualitative and quantitative imaging of the hippocampus in mesial temporal lobe epilepsy with hippocampal sclerosis

MR imaging allows the in vivo detection of hippocampal sclerosis (HS) and has been instrumental in the delineation of the syndrome of mesial temporal lobe epilepsy with HS (mTLE-HS). MR features of HS include hippocampal atrophy with an increased T2 signal. Quantitative MR imaging accurately reflects the degree of hippocampal damage.Ictal single photon emission computed tomography (SPECT) in mTLE-HS shows typical perfusion patterns of ipsilateral temporal lobe hyperperfusion, and ipsilateral frontoparietal and contralateral cerebellar hypoperfusion. Interictal 18fluoro-2-deoxyglucose positron emission tomography (PET) shows multiregional hypometabolism, involving predominantly the ipsilateral temporal lobe. 11C-flumazenil PET shows hippocampal decreases in central benzodiazepine receptor density. Future strategies to study the etiology and pathogenesis of HS should include longitudinal MR imaging studies,MR studies in families with epilepsy and febrile seizures, stratification for genetic background, coregistration with SPECT and PET, partial volume correction and statistical parametric mapping analysis of SPECT and PET images.

Mechanisms of epilepsy progression: current theories and perspectives from neuroplasticity in adulthood and development

Clinical and epidemiological studies have repeatedly demonstrated that a subset of patients with epilepsy have progressive syndromes with increasing seizure frequency and cumulative adverse effects despite optimal anticonvulsant therapy. Recent longitudinal imaging studies and long-term neuropsychological studies have confirmed that a substantial subset of people with epilepsy undergo progressive brain atrophy accompanied by functional declines that worsen with duration of epilepsy. As further evidence of the progressive and adverse effects of inadequately controlled epilepsy, chronic experimental models of epilepsy and the phenomenon of kindling have provided abundant evidence that neural circuits undergo long-term progressive structural and functional alterations in response to seizures. This long-term seizure-induced plasticity in neural circuits appears to be "bidirectional", inducing progressive damage while also inducing resistance to additional damage, as a function of timing or inter-seizure interval. Seizure-induced plasticity has pronounced age-dependence, and influences long-term cognitive consequences of seizures during early life and acquired susceptibility to epilepsy in adulthood. While it is clear from clinical and epidemiological studies that human epilepsy is a heterogeneous disorder and that not all epileptic syndromes are progressive, emerging results from studies of activity-dependent and seizure-induced plasticity and perspectives from "complex systems" analysis are providing new insights into systematic neurobiological processes that are likely to influence the progressive features of epileptic syndromes and patterns of progression in individual patients. The emerging perspective is that phenomena of plasticity and genetic background exert powerful effects in development and adulthood through regulation of activity-dependent structural and functional remodeling of neural circuitry, and that these effects not only influence progression and consequences of seizures, but also offer new opportunities for therapeutic intervention.

Neuropsychological Outcome after Selective Amygdalohippocampectomy with Transsylvian versus Transcortical Approach: A Randomized Prospective Clinical Trial of Surgery for Temporal Lobe Epilepsy

PURPOSE

Selective amygdalohippocampectomy (SAH) is a surgical treatment option for patients with medically intractable mesial temporal lobe epilepsy. In contrast to standard anterior temporal lobectomy, resection of unaffected tissue is limited, although it achieves equal seizure outcomes in selected patients. In SAH, the mesial structures can be approached by different routes, the transsylvian approach and the transcortical approach. Advantages or disadvantages with respect to postoperative cognitive outcome are still a matter of debate.

METHODS

Eighty randomized patients were included in the analyses. In 41 patients, the transsylvian approach, and in 39 patients, the transcortical approach was performed. All patients received comprehensive neuropsychological testing of verbal and nonverbal memory, attention, and executive functions before and 6 months or 1 year after SAH.

RESULTS

Seventy-five percent of patients became completely seizure free with no difference depending on the chosen approach. Repeated measures multivariate analysis of variance (MANOVA) showed that cognitive outcomes after both approaches were essentially the same. The only exception was phonemic fluency, which was significantly improved after transcortical but not after transsylvian SAH.

CONCLUSIONS

The results indicate that either surgical approach can be chosen independent of cognitive outcome criteria. Improvement in phonemic fluency after transcortical SAH may reflect selective normalization of cognitive function after epilepsy surgery, whereas frontal lobe manipulation might have hindered recovery of this function after transsylvian SAH.

Selective Posterior Cerebral Artery Amobarbital Test: Its Role in Presurgical Memory Assessment in Temporal Lobe Epilepsy

PURPOSE

To evaluate the efficacy and risk of complications of selective posterior cerebral artery (PCA) amobarbital anesthesia in memory assessment of patients with epilepsy under consideration for temporal lobe resection.

METHODS

Thirty-two candidates for temporal lobectomy in whom conclusive memory assessment could not be obtained by the standard intracarotid amobarbital procedure were submitted to a selective PCA amobarbital test. A mean dose of 75 mg amobarbital was injected via microcatheter into the P2 segment of the PCA. Ten common objects were presented for naming and remembering while the anesthesia was judged efficient. After return to neurologic baseline, recall and recognition memory were assessed.

RESULTS

In all of the 32 patients, angiography and PCA anesthesia were successfully accomplished without serious adverse events. All but one of the patients remained alert and cooperative for memory testing under the anesthesia, and 28 of these patients showed adequate memory capacity of the hemisphere contralateral to the side targeted for surgery. So far, 19 patients have proceeded to surgery, and no case of global amnesia or serious, material-specific memory impairment has resulted. Three patients failed the PCA test (fewer than 67% items correctly recognized) and were excluded from surgery, partly on the basis of the PCA test results, but also supported by an overall evaluation of all the diagnostic procedures used.

CONCLUSIONS

The selective PCA amobarbital test appears justifiable when performed by interventional neuroradiologists and may significantly reduce the risk of erroneously excluding patients with epilepsy from temporal resection. Further corroboration of the safety of the procedure seems warranted.

Early epilepsy surgery

Uncontrolled epilepsy is associated with progressive cortical and hippocampal atrophy, substantial cognitive and psychosocial morbidity, and increased mortality. Seizure freedom is required to reverse such morbidity and mortality. Surgery is vastly superior to medical therapy for patients with chronic, refractory temporal lobe seizures, and is now the standard of care for these patients. On the other hand, the concept of early surgery requires further exploration and definition. Although there is no robust, direct evidence to support early epilepsy surgery, case series and cohort studies report an association between earlier surgery and better outcomes. The evidence for earlier epilepsy surgery is reviewed.

The impact of sex and language dominance on material-specific memory before and after left temporal lobe surgery

Recent findings raised evidence that in early-onset left temporal lobe epilepsy, women show greater functional plasticity for verbal memory than men. In particular, women with lesion- or epilepsy-driven atypical language dominance show an advantage over men. The question asked in this study was whether there is evidence of sex- and language dominance-dependent late, i.e. adult age, plasticity for verbal memory when epilepsy surgery is performed in these patients. Pre- and 1-year postoperative memory performance was evaluated in 169 patients (94 males and 75 females) who underwent left temporal lobe surgery and who had WADA testing of hemispheric language dominance prior to surgery. Verbal memory and figural memory were assessed by list-learning paradigms. According to the Bonn intracarotid amobarbital test (IAT) protocol, patients were categorized into left dominant or atypically dominant (right, incomplete left or right, and bilateral dominant) groups. Results were controlled for the hypothesized sex differences. Thirty-four percent of men and 47% of women displayed patterns of atypical language dominance. Atypical dominance was related to an early onset of epilepsy. Men showed a larger time window for development of atypical dominance but, differently from women, the pattern of atypical dominance was more strictly determined by the age at onset of epilepsy. Atypically dominant women showed better verbal memory than typically dominant women or men. After surgery, right dominant patients had better verbal memory outcome than patients with bilateral or left language dominance who showed significant memory loss. No effect of sex on verbal memory change was found. Figural memory deteriorated in men and improved in women, when they were not left dominant. Seizure outcome had no effect on performance changes. It was concluded that better preserved verbal memory in atypically dominant women before surgery indicates greater benefit from atypical dominance in women than men with regard to the initial damage associated with left hemisphere epilepsy. Later in life, when epilepsy surgery causes additional damage, no such sex difference is observed, indicating that the women's advantage over men is fixed to an early time window in life. Postoperative changes in figural memory suggest dynamics in crowding and suppression patterns. Whether this reflects late plasticity and compensation needs further demonstration. For clinical practice, it is important to note that incomplete right hemisphere and bilateral language dominance do not protect against verbal memory loss after left-sided temporal lobe surgery.

Neuropsychological effects of seizures

The neuropsychological effects of seizures, including an accumulation of single attacks, on mental abilities are explored through a selective review of the world's literature. Each paper included in this review was longitudinal in nature, and in each case, formal psychological testing was accomplished both at the beginning and at the end of the study. Of the 22 investigations meeting all requirements for inclusion, 9 focused on children and 13 on adolescents and adults. Some difficulties were encountered in that the types and numbers of seizures occurring during the studies were rarely included. Except in three studies where there were very few seizures of any kind, it appears justifiable to assume that the patients in all other studies had active seizure disorders. Assuming this to be true, in 12 of the remaining 20 papers, a relationship was found between seizures and changes in mental abilities, in 5 cases the results were mixed or uncertain, and in 3 cases the available evidence was against such a relationship. Mild but definite relationships between seizures and mental decline are supported by this literature review, but these relationships require much more study, particularly with a clearer understanding of the types and frequencies of seizures experienced. Suggestions for future research are offered.

Neuropsychological aspects of epilepsy surgery

Neuropsychological evaluation of a patient's cognitive capabilities before and after epilepsy surgery is essential in elective epilepsy surgery. On the one hand, neuropsychology provides accessory information regarding the localization and lateralization of epilepsy-associated cognitive impairment; on the other hand, it is a useful tool for quality and outcome control of epilepsy surgery which helps to make surgery more effective and safe. Evaluation of the adequacy of the brain tissues to be resected and of the patient's mental reserve capacities allows for a prediction of the postoperative cognitive development. Successful surgery can stop mental decline due to chronic epilepsy and it can reverse this negative trend by release of functions and capacities that were secondarily affected before surgery. However, surgery bears the risk of additional impairments which, in interaction with normal or even pathological processes of mental aging, may accelerate cognitive decline at an older age. From a neuropsychological point of view, early recognition of pharmacoresistance is important along with early and complete seizure control with maximal sparing of functional tissues.

Advances in epilepsy

Advances in understanding of both the causes and consequences of epilepsy have been paralleled by a number of recent reports and clinical guidelines highlighting the complexities involved in both diagnosing and treating epilepsy. We review recent developments, including comments on the evolution of clinical guidelines, anti-epileptic drugs, epilepsy surgery and new treatment approaches in development. Epilepsy genetics and emerging evidence on mechanisms of drug resistance in epilepsy will also be discussed. Issues with respect to pregnancy and epilepsy are considered, together with more recently identified dilemmas including bone health in epilepsy and whether seizures themselves cause brain damage. Imaging in epilepsy has recently been reviewed elsewhere, and will not be discussed.