Practice parameter: temporal lobe and localized neocortical resections for epilepsy: report of the Quality Standards Subcommittee of the American Academy of Neurology, in association with the American Epilepsy Society and the American Association of Neurological Surgeons

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.

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.

Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

Experts discussed the definition, natural history, pathologic features, pathogenesis, electroclinical, neurophysiological, neuropsychological, structural and functional imaging findings, as well as surgical outcome in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). After a long-lasting consensus process the ILAE Commission Neurosurgery of epilepsy accepted the resulting conclusions as state-of-the art report on MTLE-HS. The majority of contributors considered MTLE-HS to represent a sufficient cluster of signs and symptoms to make up a syndromic diagnostic entity.

Clinical outcome of epilepsy surgery

PURPOSE OF REVIEW

The outcome from current surgical methods of treating drug-resistant epilepsy will be considered, looking at changes in classical resective surgery and new methodology being introduced in the functional treatment of these patients.

RECENT FINDINGS

There is now class I evidence that temporal lobe surgery is effective. Sophisticated and appropriate magnetic resonance imaging sequences, together with an assessment of the electroclinical syndrome, allow patients to be assessed for resective surgery. The concept of 'surgically remediable syndromes' determines the type of procedure that is effective for particular patients. Technical advances such as neuronavigation techniques and intra-operative magnetic resonance imaging have improved the effectiveness of these procedures. Other techniques of disconnection, such as multiple subpial transection, and stimulation both indirectly using the vagus nerve and directly using various intracranial targets, are currently effective and have potential for future development.

SUMMARY

This review will demonstrate that current surgical techniques are safe and effective in relieving drug-resistant epilepsy.

The multicenter study of epilepsy surgery: recruitment and selection for surgery

PURPOSE

Multiple studies have examined predictors of seizure outcomes after epilepsy surgery. Most are single-center series with limited sample size. Little information is available about the selection process for surgery and, in particular, the proportion of patients who ultimately have surgery and the characteristics that identify those who do versus those who do not. Such information is necessary for providing the epidemiologic and clinical context in which epilepsy surgery is currently performed in the United States and in other developed countries.

METHODS

An observational cohort of 565 surgical candidates was prospectively recruited from June 1996 through January 2001 at six Northeastern and one Midwestern surgical centers. Standardized eligibility criteria and protocol for presurgical evaluations were used at all seven sites.

RESULTS

Three hundred ninety-six (70%) study subjects had resective surgery. Clinical factors such as a well-localized magnetic resonance imaging (MRI) abnormality and consistently localized EEG findings were most strongly associated with having surgery. Of those who underwent intracranial monitoring (189, 34%), 85% went on to have surgery. Race/ethnicity and marital status were marginally associated with having surgery. Age, education, and employment status were not. Demographic factors had little influence over the surgical decision. More than half of the patients had intractable epilepsy for >/=10 years and five or more drugs had failed by the time they initiated their surgical evaluation. During the recruitment period, eight new antiepileptic drugs were approved by the Food and Drug Administration for use in the United States and came into increasing use in this study's surgical candidates. Despite the increased availability of new therapeutic options, the proportion that had surgery each year did not fluctuate significantly from year to year. This suggests that, in this group of patients, the new drugs did not provide a substantial therapeutic benefit.

CONCLUSIONS

Up to 30% of patients who undergo presurgical evaluations for resective epilepsy surgery ultimately do not have this form of surgery. This is a group whose needs are not currently met by available therapies and procedures. Lack of clear localizing evidence appears to be the main reason for not having surgery. To the extent that these data can address the question, they suggest that repeated attempts to control intractable epilepsy with new drugs will not result in sustained seizure control, and eligible patients will proceed to surgery eventually. This is consistent with recent arguments to consider surgery earlier rather than later in the course of epilepsy. Postsurgical follow-up of this group will permit a detailed analysis of presurgical factors that predict the best and worst seizure outcomes.

Long-term outcome of nonsurgical candidates with medically refractory localization-related epilepsy

PURPOSE

Epilepsy surgery can result in complete seizure remission rates of upto 80% in patients with mesial temporal sclerosis and unilateral seizures. The seizure-free rate after surgery for patients with extratemporal nonlesional epilepsy has ranged between 30% and 40%. Some patients with medically refractory localization-related epilepsy cannot be offered surgical resection because of inadequate localization of the epileptogenic zone, documentation of bilateral ictal onsets, or functionally important areas of cortex that prohibit resection. The short-term rate of complete remission with medications in temporal lobe epilepsy is poor. Less is known about remission rates in patients who are not surgical candidates. In this study, we evaluated the outcome of medical treatment in patients with medically refractory partial epilepsy who were evaluated for possible epilepsy surgery but deemed to be inadequate surgical candidates.

METHODS

A retrospective chart review and telephone survey with a self-rating questionnaire were completed for all patients who underwent epilepsy surgery evaluation but were not ultimately offered surgical treatment at the University of Michigan from 1990 through 1998. We assessed changes in seizure frequency and type, imaging characteristics, ictal recordings, interim medication history, and subjective changes in quality of life.

RESULTS

Thirty-four subjects were available for follow-up study, at an average of >4 years after surgical evaluation. A significant reduction in seizure frequency was noted at the time of follow-up compared with that at the time of surgical evaluation. Of patients, 21% achieved seizure remission and remained seizure free for an average of 2.5 years. Four of the seven seizure-free patients attributed their remission to new antiepileptic drugs (AEDs). On a global self-rating item, 15 of 34, or 44%, felt more or much more satisfied with their lives, and 41% felt their quality of life was stable.

CONCLUSIONS

A surprisingly large number of patients we surveyed, with refractory partial epilepsy not eligible for surgical management, reported reduced seizure frequency at follow-up, and 21% were seizure free. Our findings suggest that the long-term prognosis in patients with refractory partial epilepsy who are not surgical candidates may be more positive than might be generally expected.

Understanding the delay before epilepsy surgery: who develops intractable focal epilepsy and when?

Intractable temporal lobe epilepsy that is surgically treated in adulthood is a disorder whose onset frequently occurs during childhood and early adolescence. The average duration of epilepsy prior to surgery is on the order of 20 years. The long delay between onset and surgery has at least two components: time from onset to intractability and time from evidence of intractability to surgery. The first interval is prolonged >10 years especially if the onset is during childhood. This suggests a complex natural history that we have not fully appreciated as well as a potential window of opportunity for early secondary intervention. The second interval is also prolonged, especially if onset was during childhood. Reasons for this are not fully clear but may include a reluctance to consider surgery and perhaps difficulty deciding whether seizures are sufficiently intractable to warrant surgery especially after what may have been a relatively benign initial course. Factors involved in the second delay need to be better understood so that surgical interventions can be appropriately targeted early rather than late, thereby reducing serious social, psychological, and educational consequences associated with uncontrolled seizures.

Effectiveness and safety of epilepsy surgery: what is the evidence?

Evidence from a recent randomized controlled trial of surgical versus medical therapy of temporal lobe epilepsy proves that antero-mesial resection is safe and more effective than medical therapy. The number of patients needed to treat for one patient to become free of disabling seizures is two, which is superior to most interventions in neurology. A meta-analysis of non-randomized trials gives almost identical results; about two-thirds of patients become seizure-free, compared with only 8% with medical therapy. The results are remarkably similar among studies from different parts of the world. Quality of life improves early after epilepsy surgery, the improvements are both statistically and clinically significant, and they are sustained. Surgical morbidity with clinically important permanent sequelae is 2%. Epilepsy surgery remains underutilized in developed countries and it does not exist in all but a few developing countries. Current randomized trials are underway to explore the effect of early surgery versus optimum medical therapy on the prevention of disability in patients with mesial temporal lobe epilepsy, and to examine the effectiveness of novel interventions, such as minimally invasive surgery and brain stimulation.

The goal of epilepsy therapy: no seizures, no side effects, as soon as possible

Epilepsy is a significant health problem. Ten percent of people living a normal lifespan will experience at least one epileptic seizure and one third will develop a chronic epileptic condition. At any given time, 0.5% to 1% of the world's population has active epilepsy, amounting to over 40 million people. A World Health Organization-sponsored study determined that epilepsy accounts for 1% of the global burden of disease, measured as disability-adjusted life years equivalent to the global burden of lung cancer in men and to breast cancer in women. Disability-adjusted life years measure years of productivity lost as a result of disability or death, which is relatively high for epilepsy because this condition often begins in childhood. The cost of epilepsy in the United States has been estimated at $12.5 billion/year, and 80% of this cost is borne by the 30% of patients whose seizures are not controlled.

The cost of uncontrolled epileptic seizures to society, and to individuals with epilepsy and their families, is measured not only in economic terms, but also in terms of human suffering. In this month's first article, Michael R. Sperling, MD, who has authored seminal papers on consequences of epilepsy, provides evidence that epilepsy is not a benign disorder; that early control of epileptic seizures is important to avoid irreversible disability due to the development of psychological and social disturbances and progressive cerebral dysfunction, as well as epilepsy-related death. The burden imposed on society and on individuals by uncontrolled epileptic seizures is all the more tragic because many suffer needlessly. For a significant number of adults who have had recurrent seizures since infancy, childhood, or adolescence, more aggressive early intervention might have rescued them from a lifetime of disability. Consequently, the goal of therapy today should be no seizures and no side effects, as soon as possible.

Seizure Recurrence after Planned Discontinuation of Antiepileptic Drugs in Seizure-free Patients after Epilepsy Surgery: A Review of Current Clinical Experience

PURPOSE

Although epilepsy surgery, especially temporal lobe epilepsy surgery, is well established to control seizures in patients remaining on antiepileptic drug (AED) treatment, less information is available about how many seizure-free surgical patients will relapse after discontinuation of AEDs under medical supervision.

METHODS

A literature review yielded six retrospective clinical observations.

RESULTS

After planned discontinuation of AEDs in patients rendered seizure free after epilepsy surgery, most often various forms of temporal lobe surgery, the mean percentage recurrence rate in adults in four studies was 33.8%[95% confidence interval (CI), 32.4-35.2%], with maximum follow-up ranging from 1 to 5 years. Seizure recurrence increased during the follow-up of 1 to 3 years and occurred within 3 years of AED discontinuation. In one study of children with temporal lobe epilepsy, the recurrence rate was 20%. More than 90% of adult patients with seizure recurrence regained seizure control with reinstitution of previous AED therapy. Seizure recurrence was unaffected by the duration of postoperative AED treatment; as a consequence, delaying discontinuation beyond 1 to 2 years of complete postoperative seizure control seems to have no added benefit. The occurrence of rare seizures or auras after surgery did not eliminate the possibility of eventual successful AED discontinuation.

CONCLUSIONS

AED discontinuation is associated with a seizure recurrence in one in three patients rendered seizure free by epilepsy surgery. These results will be useful in counseling patients about discontinuing AED treatment after successful epilepsy surgery.

Barriers to the management of patients with surgically remediable intractable epilepsy

It is estimated that only a small proportion of patients with surgically remediable intractable epilepsy receive surgical treatment. There are multiple reasons why this is the case. Patients with intractable epilepsy are sometimes severely disabled and disability can create barriers to getting recommended care. Patients with epilepsy are not well informed about their condition and the available treatments. The incidence of epilepsy is similar in minority populations, and surgically remediable epilepsy frequently presents in adolescence. Nevertheless, these vulnerable populations have specific barriers to receiving epilepsy care, which are often not addressed. In addition, despite scientific evidence for the benefits of the surgical treatment of epilepsy, many healthcare providers do not recommend or adequately discuss surgery with patients. Solutions to these barriers will require interventions that result in informed and capable patients who actively participate in their care and healthcare providers who practice culturally sensitive, recommended care.

The impact of temporal lobe surgery on cure and mortality of drug-resistant epilepsy: summary of a workshop

The Third International Spring Epilepsy Research Conference took place in Georgetown, Cayman Islands from April 26 to May 3, 2003. One workshop discussed the impact of epilepsy surgery on seizure outcome and mortality of antiepileptic drug (AED)-resistant temporal lobe epilepsy. This article summarizes the information presented at this workshop. Although two-thirds of adult patients undergoing epilepsy surgery become seizure-free with continued AED treatment, current clinical experience shows that seizure recurrence occurs in one-third of patients when AEDs are withdrawn under medical supervision. Additional seizure recurrence occurring after AED taper, poor drug compliance and even while patients continue on AEDs after surgery leave only approximately one-third of patients cured after temporal lobe resection. Mostly because so many patients prefer to stay on AEDs although they are free of disabling seizures after surgery, a randomised controlled trial of AED discontinuation is needed to determine if in fact only one-third of patients are cured after surgery. Based on the functional anatomy of temporal lobe surgery two hypotheses are presented why only a minority of patients are cured after surgery. The type and the prognostic significance of seizures after surgery is discussed. Recent studies have suggested that successful temporal lobe surgery may be able to normalize the increased standard mortality ratio (SMR) of drug-resistant temporal lobe epilepsy. However, pre-existing differences in SMR between those cured and those not cured by temporal lobe surgery and other unresolved methodological issues make it difficult at present to fully evaluate the impact of surgery on mortality. Future studies are thus warranted to specifically address the impact of temporal lobe surgery on cure and mortality.

How effective is surgery to cure seizures in drug-resistant temporal lobe epilepsy?

It is well recognized that two-thirds of patients with drug-resistant temporal lobe epilepsy will be free of disabling seizures with continued medical treatment after temporal resection. Seizure recurrence has been noted during a five-year follow-up in approximately one-third of these seizure-free patients mostly but not exclusively following planned complete discontinuation of antiepileptic drugs (AEDs). This leaves one-third of patients without disabling seizures and without AEDs several years after surgery. Despite improvements in seizure frequency or severity, seizures persist in another third of patients undergoing surgery. Although cure (five years without any seizures and off AEDs) is the ultimate aim of epilepsy surgery, the percentage of patients cured by surgery cannot be well defined at the moment. We need a long-term randomized controlled trial on AED discontinuation in seizure-free patients followed by long-term open extension to determine if only one in three adult patients with drug-resistant temporal lobe epilepsy is cured by surgical intervention.