The first major multicenter study to examine this issue analyzed data retrospectively from over 1,000 adults who had undergone temporal lobe resective surgery in eight centers in the United States6 and had full pre- and postoperative neuropsychological assessments. Only 24 patients (2.3%) had an IQ less than 70, highlighting the tendency for such patients to not receive resective surgical treatment. This study did show a relationship between preoperative IQ and seizure outcome, but the effect was modest. Indeed the remission rate in those with an IQ less than 70 was 54.2%, and was 73.2% for those with a borderline IQ level. This emphasizes that although a lower IQ may predict a slightly worse outcome in some, there are a significant proportion of patients who can derive great benefit. The poorest outcome in this study was in those with a low IQ who had a structural lesion other than hippocampal sclerosis.
Several other small studies have also addressed this issue of preoperative IQ level and outcome following surgery. In 16 adults with an IQ less than 85, Gleissner and colleagues7 found a remission rate of 64%, with no deterioration in neuropsychological function and some positive socioeconomic outcomes. The main predictor of a poor outcome was a left-sided lesion, which is likely to be because the surgery in the dominant hemisphere was more restricted.
The same group examined 285 consecutive children who underwent resective epilepsy surgery, and examined the outcome in relation to IQ level.8 Twenty-one patients (7.4%) had an IQ less than 70, with 24 (8.4%) of below average level (IQ 71-85). There was no significant difference between these groups and those with an average IQ in terms of seizure outcome one year after surgery, with 67% seizure free in the low IQ group, 77% of those with a borderline IQ, and 78% in the group with average intelligence. No change was found in neuropsychological testing, other than an improvement in executive functioning of those with a low IQ. Attention improved and behavioral problems were less marked postoperatively in all groups.
Bjornaes and colleagues9 found a remission rate of 48% in 31 patients with an IQ less than 70 who underwent resective surgery. Remission was more likely in those with temporal compared with extratemporal epilepsy (52% versus 38%), but the main factor predictive of outcome was the duration of epilepsy. In those with epilepsy for less than 12 years, 80% were seizure free. This raises the crucial issue of timing of epilepsy surgery in general, but in particular in this group with ID. It is well known that chronic refractory epilepsy has a negative neuropsychological and psychosocial effect, and it may be that rather than excluding patients with ID from the option of curative treatment, we should be more aggressive at an earlier stage.
There is a significantly higher rate of psychiatric problems in patients with epilepsy than the general population, particularly in those with drug-refractory partial epilepsy. A mood disorder is very common in such patients, and depending on the definition used, may occur in up to 75% of patients10; anxiety has been reported in over 40%11 of individuals with refractory epilepsy. Suicide rates may be up to 25 times more common in patients with temporal lobe epilepsy compared with people without epilepsy.12 It has been recognized that psychiatric symptoms may worsen or appear de novo following epilepsy surgery, and so surgery is often undertaken with extreme caution or refused on the grounds of pre-existing psychiatric problems. This issue may be of particular relevance to the ID population with epilepsy where behavioral problems and other psychiatric symptoms may coexist. Many clinicians may have reservations about epilepsy surgery in a patient with ID for the reasons already stated, and if they have psychiatric symptoms in addition, the patient is often rejected for surgery.
However, some reports have suggested that the psychiatric status of epilepsy patients is either not influenced, or may even improve, following epilepsy sur-gery1314 and that even patients with chronic psychosis may have a successful outcome.15 The evidence for the psychiatric outcome in patients with ID is limited, but one of the studies examining the seizure outcome in patients with different IQ scores commented on an overall improvement in behavioral problems in patients with ID.8
A study of 226 consecutive patients who underwent epilepsy surgery at a single center showed a favorable psychiatric outcome overall1 6 but did not specifically examine patients with ID. There was a high proportion (34.5%) of some psychiatric disturbance preoperatively, with psychosis in 16%. In 22 patients (28%) the psychiatric symptoms resolved post surgery; the main symptom was postictal psychosis, which suggests that this may be a factor favoring surgery. Thirty-nine patients (50%) had a persistence of psychiatric symptoms postoperatively, and the symptoms appeared de novo in 17 (22%). In many of those patients with new-onset psychiatric symptoms there were detectable personality traits presurgery that would predispose to psychiatric problems, which has been reported previously." De novo postsurgery psychosis has been reported to be more common in nondominant resections18 • 19 and some tumors such as gangliogliomas,20 but this has not been confirmed in other studies.16 Major depressive episodes may occur following epilepsy surgery, but these are usually transitory and in individuals with a history of a milder mood disorder.17
Despite concerns over performing surgery in patients with ID, recent evidence, albeit from small studies, suggests that a low IQ should not itself be an exclusion factor for resective epilepsy surgery. There may be a trend for patients who have more severe ID to have a slightly worse outcome, but still a significant proportion derive great benefit, with no evidence of worsening cognitive performance or behavior. However, further studies on this issue are required in larger numbers to confirm these findings and also to examine whether patients with a more severe ID may also benefit from resective surgery, as the data for the group with an IQ less than 50 are very limited. It seems intuitive that if surgery is to be considered, it should be undertaken as early as possible, rather than waiting for years of chronic drug-refractory epilepsy and the consequential negative impact that this has, particularly on a child's development. This will require a fundamental shift in thinking outside of specialist centers, as currently many such patients may be managed in the community or by psychiatrists with an interest in ID and may never have access to neurological and specialist epilepsy services.
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