Brain Advance Access originally published online on December 5, 2007
Brain 2008 131(2):535-542; doi:10.1093/brain/awm296
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Seizure outcome after resective epilepsy surgery in patients with low IQ
1Institute of Neuroscience and Physiology, Epilepsy Research Group, 2Institute of Clinical specialities, Department of Paediatrics, Sahlgrenska Academy at Göteborg University, Göteborg, Sweden and 3Department of Clinical Neurophysiology, Akademiska University Hospital, Uppsala, Sweden
Correspondence to: Kristina Malmgren, Institute of Neuroscience and Physiology, Epilepsy Research Group, Sahlgrenska Academy at Göteborg University, Guldhedsgatan 19, 1 tr, SE 413 45 Göteborg, Sweden E-mail: Kristina.malmgren{at}neuro.gu.se
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Summary |
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Epilepsy surgery has been questioned for patients with low IQ, since a low cognitive level is taken to indicate a widespread disturbance of cerebral function with unsatisfactory prognosis following resective surgery. The prevalence of epilepsy in patients with cognitive dysfunction is, however, higher than in the general population and the epilepsy is often more severe and difficult to treat. It is therefore important to try to clarify whether IQ predicts seizure outcome after resective epilepsy surgery. The Swedish National Epilepsy Surgery Register, which includes data on all epilepsy surgery procedures in Sweden since 1990, was analysed for all resective procedures performed 1990–99. Sustained seizure freedom with or without aura at the 2-year follow-up was analysed as a function of pre-operative IQ level categorized as IQ <50, IQ 50–69 and IQ
70 and was also adjusted for the following variables: age at epilepsy onset, age at surgery, pre-operative seizure frequency, pre-operative neurological impairment, resection type and histopathological diagnosis. Four hundred and forty-eight patients underwent resective epilepsy surgery in Sweden from 1990 to 1999 and completed the 2-year follow-up: 72 (16%) had IQ <70, (18 with IQ <50 and 54 with IQ 50–69) and 376 IQ 70. There were 313 adults and 135 children 
18 years. Three hundred and twenty-five patients underwent temporal lobe resections (TLR) and 123 underwent various extratemporal resections (XTLR). At the 2-year follow-up, 56% (252/448) of the patients were seizure free: 22% (4/18) in the IQ <50 group, 37% (20/54) in the IQ 50–69 group and 61% (228/376) in the IQ 70 group. There was a significant relation between IQ category and seizure freedom [odds ratio (OR) 0.41, 95% confidence interval (CI) 0.27–0.62] and this held also when adjusting for clinical variables [OR 0.58 (95% CI 0.35–0.95)]. In this population-based epilepsy surgery series, IQ level was shown to be an independent predictor of seizure freedom at the 2-year follow-up. However, many of the low-IQ patients benefit from surgery, especially patients with lesions. Low IQ should not exclude patients from resective epilepsy surgery, but is an important prognostic factor to consider in the counselling process.
Key Words: epilepsy surgery; focal epilepsy; seizure outcome; low IQ
Abbreviations: AED, antiepileptic drug; FLR, frontal lobe resection; HE, hemispherectomy; MLR, multilobe resection; OLR, occipital lobe resection; PLR, parietal lobe resection; RCPM, Raven Coloured Progressive Matrices; TLR, temporal lobe resection; WAIS-R, Wechsler Adult Intelligence Scale-Revised; WISC, Wechsler Intelligence Scale for Children; WPPSI-R, Wechsler Preschool and Primary Scale of Intelligence-Revised
Received June 14, 2007. Revised September 28, 2007. Accepted November 14, 2007.
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Introduction |
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Resective surgery for pharmacoresistant focal epilepsy is recognized as a valuable treatment option in carefully selected patients (Wiebe et al., 2001
). A low IQ has for a long time been considered a contraindication to resective epilepsy surgery (Falconer, 1973; Engel Jr and Shewmon, 1993a; Engel Jr, 1996). The assumption has been that low intellectual functioning indicates bilateral or diffuse brain damage and hence less probability of a good seizure outcome. Intellectually, impaired persons have also been considered to be at special risk with respect to post-operative cognitive outcome (Rausch, 1991).
Few investigations have focused on the results of resective epilepsy surgery in patients with IQ <70 and it seems that at least in adults, temporal lobe resection (TLR) is seldom considered an option for patients with low IQ. In a multicentre study of 1034 TLR patients from eight epilepsy surgery centres in the US, only 2.3% of the patients had IQ <70 (Chelune et al., 1998). In the epilepsy surgery series from the National Hospital for Neurology and Neurosurgery, London, 1.6% of 321 adult TLR patients had VIQ <70 and 3.8% had PIQ <70 (personal communication from Sallie Baxendale) and in the Bonn adult series of TLR patients the corresponding proportion was 2% (personal communication from Ulrike Gleissner). In contrast, learning disability is a common finding in paediatric epilepsy surgery patients: in one study of TLR in children 47% had learning disability, which was mild in 8%, moderate in 22% and severe in 17% (McLellan et al., 2005).
In the paediatric epilepsy surgery literature, there are several reports on epilepsy surgery in patients with low IQ demonstrating good seizure outcome, comparable to that in patients with normal IQ (Levisohn, 2000). In a consecutive series of children <19 years operated in Göteborg of which 65% became seizure free or had a >75% reduction of seizure frequency, 54% had an IQ level <70 (Olsson et al., 2005). Many reports, however, focus on specific aspects of epilepsy surgery in children, like tuberous sclerosis (Jarrar et al., 2004), malformation of cortical development (Hamiwka et al., 2005), hemispherectomies (HEs) (van Empelen et al., 2004; González-Martinez et al., 2005) and do not particularly address the question of epilepsy surgery and learning disabilities.
The aim of the present study was to analyse data from the population-based Swedish National Epilepsy Surgery Register 1990–99 with regard to resective epilepsy surgery and IQ in adults and children and to test the hypothesis that there is an independent relation between seizure outcome at the 2-year follow-up and pre-operative IQ category. Secondary aims were to relate surgical complications and histopathological diagnoses to IQ category. We chose to use IQ level instead of the terms mental retardation or learning disability, IQ level being a pragmatic way of describing the impairment of cognitive functioning in the patient group. It has also been used in this way by others before, thus making comparisons between studies possible (Chelune et al., 1998; Gleissner et al., 1999; Freitag and Tuxhorn, 2005; Gleissner et al., 2006).
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Methods and Patients |
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Every epilepsy surgery procedure in Sweden is reported to the Swedish National Epilepsy Surgery Register from a defined start of the assessment. The register was initiated by the Swedish Board of Health and Welfare as a quality control register and is controlled by the Swedish Data Inspection Board. All patients whose data are included in the register have given their informed consent. The register protocol includes data on the patients’ social situation, epilepsy history, pre-operative seizure situation defined as the mean seizure frequency during the year preceding the pre-surgical investigation, and pre-operative anti-epileptic drug (AED) medication. IQ level is categorized as IQ <50, IQ 50–69 or IQ
70 based on the pre-operative neuropsychological assessments, which are, however, not included in the database. The choice of methods and cut-off levels have been agreed upon by all neuropsychologists from the six operating centres at several consensus meetings. The individual's level of functioning and estimated mental age rather than the chronological age are taken into consideration when choosing the method for assessment. For the IQ assessments, age appropriate Wechsler Intelligence scales are used: the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R), (Wechsler, 1999), the Wechsler Intelligence Scale for Children (WISC) (WISC-III, 1994) and the Wechsler Adult Intelligence Scale-Revised (WAIS-R) (Wechsler, 1981; Bartfai et al., 1992). Griffiths’ Developmental Scales (Swedish version), (Alin-Åkerman and Norberg, 1991) are used to score infants and children according to developmental age. Raven Coloured Progressive Matrices (RCPM), (Raven, 1965, 1974) are applied for a few children in the 5 to 11-year-old range when the WPPSI or WISC would be inappropriate.
Co-existing neurological deficits or impairments are also reported to the register. Further items include investigational findings, side and site of the operation, histopathological diagnoses, complications during the pre-surgical evaluation or at surgery, and a 2-year follow-up of seizure outcome, AED medication and psychosocial data. At the 2-year follow-up, seizure freedom is defined as no seizures (or auras only) since surgery (immediate post-operative seizures excluded), which corresponds to Engel classes I a and I b (Engel Jr et al., 1993b) or to classes 1 and 2 in the International League Against Epilepsy (ILAE) proposal for a new classification of surgical outcome (Wieser et al., 2001). In this study, we have chosen to report seizure freedom with or without aura, since it is considered unlikely that auras are consistently reported by all patients with low IQ. For patients with continuing seizures post-operatively, the mean seizure frequency during the year preceding the follow-up is reported and the change (reduction or, in a few cases, increase) pre- to post-operatively is reported in percent. The following seizure outcome categories have been used: (i) seizure free (with or without aura); (ii) >75% reduction of seizure frequency; (iii) 50–75% reduction of seizure frequency; (iv) 0–50% reduction of seizure frequency and (v) increased seizure frequency.
All surgical complications are reported to the register and are graded as major or minor as described earlier (Rydenhag and Silander, 2001). A complication is defined as an unwanted, unexpected and uncommon event after a diagnostic or therapeutic procedure. (Hence, an expected worsening of a hemiparesis after a HE and an upper quadrantanopia after a temporal lobe resection are not regarded as complications.) The severity of a complication is graded as major or minor, major if it lasts longer than 3 months and affects the activities of daily living. Significant neurological deficits are also defined as major, even if activities of daily living are not affected.
The validity of the data collected from the centres is regularly checked by several systems. Intrinsic checkpoints within the database reject certain impossible combinations. An external revision is regularly performed: two epilepsy nurses visit all centres and compare the data entered into the data base with the original data from the patient files for a random yearly sample of the patients operated at each centre. The items controlled in this external revision include side and site of operation, complications, main histopathological findings and seizure outcome at the 2-year follow-up. So far, there have been no mismatches in the reporting on any of these central items.
For the purpose of this study, the main histopathological diagnoses were categorized into four groups: lesions, cortical malformations, gliosis and other diagnoses. Lesions included gangliogliomas, dysembryoplastic neuroepithelial tumour (DNET), low grade astrocytomas and cavernomas. Cortical malformations encompassed both major malformations and microdysgenesis (Nordborg et al., 1987). Gliosis included atrophic-gliotic lesions but also mesial sclerosis, since this was not a separate diagnostical entity in the register protocol until 1995. Other diagnoses included cases of tuberous sclerosis, epidermoid, Sturge–Weber and a few other vascular malformations.
Statistical analysis
A univariate logistic regression was performed between the dependent variable seizure freedom and the independent variable IQ to determine whether IQ was an independent predictor in the unadjusted model. Then a multiple logistic regression was performed to determine if IQ was an independent predictor in the model adjusted for the following clinical variables: age at epilepsy onset, age at surgery, pre-operative seizure frequency, pre-operative neurological impairment (yes or no), resection type (dichotomized as TLR or XTLR) and histopathological diagnosis (dichotomized as lesion or no lesion).
IQ was then reparameterized into two variables to describe the change in odds ratio (OR) from IQ 70 to IQ 50–69 and from IQ 70 to IQ<50. Then a multiple logistic regression was performed to determine the OR in the unadjusted and adjusted models.
Area under ROC curve (c-statistics) was calculated for description of goodness for the model.
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Results |
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Description of the series
In the present study, data on all patients who had undergone resective epilepsy surgery in Sweden during the 10-year period from 1990 to 1999 were analysed. Five hundred and one procedures were identified of which 53 patients had not been subjected to 2-year follow-up. In 28 cases, this was due to re-operation during the period, four patients turned out to have malignant tumours and were therefore excluded, six were lost to follow-up because they had moved abroad, 11 had not been able to undergo the 2-year follow-up due to miscellaneous causes and six patients died within the first two post-operative years. The causes of death were the following: a perioperative haematoma in one case, malignified astrocytoma in two cases, probable SUDEP in two cases and unknown in one case. The analysis was based on data from the 448 patients who completed the 2-year follow-up. Of the 448 patients, 313 were adults (>18 years) and 135 were children (
18 years) at the time of surgery. Eighteen patients (4.0%) had an IQ <50 (one adult and 17 children), a mean age at surgery of 8.8 years (range 1.9–36 years) and a mean age at epilepsy onset of 0.8 years (range 0.1–3 years). Fifty-four patients (12.1%) had an IQ between 50 and 69 (24 adults and 30 children), a mean age at surgery of 18.4 years (range 1.4–45 years) and a mean epilepsy onset age of 4.5 years (range 0–41 years). Three hundred and seventy-six patients (83.9%) had an IQ 70 (288 adults and 88 children), a mean age at surgery in this group of 29.3 years (range 0.6–60 years) and a mean epilepsy onset age of 14.1 years (range 0–53 years). The baseline seizure frequency was higher in patients who had XTLR than in those who had TLR and irrespective of resection type the low IQ patients had a higher seizure frequency at baseline than the patients with IQ 70 (Table 1).
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Surgical procedures and complications
The distribution of surgical procedures in the different IQ groups is shown in Fig. 1, which illustrates that the extensive resections (multilobar resections and HEs) were mainly performed in the low-IQ groups, while proportionally more patients in the IQ
70 group underwent TLR. In all groups, TLR was the most common procedure.
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Of the 448 patients in this series, nine (2%) experienced a major unexpected complication (hemiparesis in seven patients, hemianopia in two). Seven of these nine patients were in the IQ
70 group (resulting in a complication rate for this group of 1.9%), two in the IQ 50–70 group (3.7%) and none in the IQ <50 group. If divided into age groups, there were seven major complications in patients >18 years (N = 313) giving a complication rate of 2.2% and two in patients 18 years (N = 135) giving a complication rate of 1.5%. Of the minor complications, 17 resolving neurological deficits were reported in the IQ 70 group (4.5%) and two in the IQ 50–70 group (3.7%) and none in the IQ <50 group.
Seizure outcome
In the whole series and across all resection types, the seizure outcome at the 2-year follow-up was as follows: 56% seizure free (252/448), 17% (74/448) with >75% reduction of seizure frequency, 11% (50/448) with 50–75% reduction of seizure frequency, 13% (59/448) with <50% reduction of seizure frequency and in 3% (13/448) there was an increase in seizure frequency. As shown in Fig. 2 the proportion of seizure free patients was lowest in the IQ <50 group and highest in the IQ 70 group: 22% (4/18) in the IQ <50 group were seizure free 2 years after surgery versus 37% (20/54) in the IQ 50–69 group and 61% (228/376) in the IQ 70 group. Additionally, 22% (4/18) in the IQ <50 group, 26% (14/54) in the IQ 50–69 group and 15% (56/376) in the IQ 70 group obtained a reduction of seizure frequency of >75%. Fifty to seventy-five percent reduction of seizure frequency was obtained by 33% (6/18) in the IQ <50 group, 17% (9/54) in the IQ 50–69 group and 9% (35/376) in the IQ 70 group. The seizure outcome was below 50% reduction of seizure frequency in 11% (2/18) of the IQ <50 group, 17% (9/54) of the IQ 50–69 group and 13% (48/376) of the IQ 70 group and in a total of 13 patients there was an increase in seizure frequency (11% or 2/18 in the IQ <50 group, 4% or 2/54 in the IQ 50–69 group and 2% or 9/376 in the IQ 70 group).
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When seizure freedom was related to main histopathological diagnoses, 79% (85/108) of all of the patients with lesions were seizure free, while 54% (26/67) of those with cortical malformations, 50% (108/218) of those with gliosis and 42% (23/55) of those with other diagnoses were free from seizures. The histopathological diagnoses were unevenly distributed in the different IQ groups. In the two low IQ groups, there were proportionally fewer cases with lesions than in the IQ
70 group and more cortical malformations and other diagnoses (Table 2). When seizure outcome was related to histopathological diagnoses, the lesional cases had the best outcome across all three groups. Seizure freedom was obtained in the single patient with a lesion and IQ <50, in three of the five patients with lesions and IQ 50–69 and in 78% (81/102) of the patients with lesions and IQ 70. In the TLR subgroup, 62% of the adults and 60% of the children were seizure free 2 years after TLR and seizure freedom in relation to main histopathological diagnoses is illustrated for adults and children, respectively in Table 3.
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IQ was shown to be an independent predictor of seizure outcome 2 years after epilepsy surgery in the unadjusted model [OR 0.41, 95% confidence interval (CI) 0.27–0.62, P < 0.0001] as well as in the model adjusted for age at epilepsy onset, age at surgery, pre-operative seizure frequency, pre-operative neurological impairment, resection type and histopathological diagnosis (OR 0.58, 95% CI 0.35–0.95, P = 0.0317). When IQ was reparametrized into two variables to describe the change in OR when IQ changed from IQ
70 to IQ 50–69 and from IQ 70 to IQ <50, both IQ variables were significant predictors of seizure outcome. When adjusting for the same clinical variables as above, the two IQ variables did not separately predict seizure outcome. The model with IQ as an independent predictor was still significant (P-value simultaneously = 0.0292) as illustrated in Table 4.
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Discussion |
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The prevalence of epilepsy in patients with cognitive dysfunction is higher than in the general population and the epilepsy is often more severe and difficult to treat. Forsgren et al. (1990
) found active epilepsy in 20.2% of all mentally retarded children and adults in northern Sweden, and 27% of these patients had daily to weekly seizures. In an unselected population of Finnish children with epilepsy, mental retardation occurred in 31.4% (Sillanpää, 1992). In a population-based study of children with mental retardation in Göteborg, Sweden, 45% had intractable epilepsy, defined as seizures at least weekly (Steffenburg et al., 1996). In a community sample of individuals with autism and mental retardation, followed from childhood to adulthood, 38% had epilepsy. In these patients, epilepsy was considered to be the factor of greatest impact on the person's daily life by a third of the carers (Danielsson et al., 2005).
Several recent paediatric epilepsy surgery reports have included children with low cognitive level. In the study by Freitag and Tuxhorn, where 70% of 50 children had IQ <70, seizure outcome was more favourable in the less retarded children. However, even in the group of severely retarded children almost half became seizure free (Freitag and Tuxhorn, 2005). Few studies focus specifically on the surgical outcome in children with intellectual disability but in one recent study three groups of patients were compared with regards to seizure as well as cognitive outcome: one group with IQ <70, one group with IQ 70–84 and one group with IQ >85. The authors found that seizure outcome or post-operative cognitive development did not depend on IQ level (Gleissner et al., 2006).
To our knowledge, only two earlier studies have explicitly focused on seizure outcome after resective epilepsy surgery in adults with cognitive impairment. In the US multicentre study, only 24 out of 1034 individuals who underwent TLR had an IQ of 50–69 (and none had an IQ <50). These patients had a seizure free outcome in 54% as compared to 76% in the total series (Chelune et al., 1998). In the study by Bjørnæs et al. (2004), of 31 patients with IQ <70 who underwent resective surgery for intractable epilepsy, 52% of those who underwent TLR (12/23) had a seizure free outcome. Hence, these studies indicate that seizure free rates after TLR may be somewhat lower in patients with low IQ, but the number of patients is very limited.
Our study represents the largest series of low-IQ patients in a population-based epilepsy surgery program, with 72 patients out of 448 (16%, 8% of the adults and 35% of the children) with IQ <70. IQ was shown to be an independent predictor of seizure outcome and this held true also when adjusting for possible confounding clinical variables. In the unadjusted model with two variables (from IQ 70 to IQ 50–69 and from IQ 70 to IQ <50), each of these variables independently predicted seizure outcome, demonstrating lower odds for the patients with IQ <50 to become seizure-free than for the patients with IQ 50–69. Hence, the assumption that low intellectual functioning per se is indicative of a lower probability of good seizure outcome was shown to be true.
There is a methodological problem associated with the use of different methods to assess IQ, which is a limit to this study. However, it was unavoidable in this series of both adults and children, where the methods had to be appropriate not only for the chronological age but also for the mental age and the level of functioning. The long study period also raises problems in this respect, since Griffiths’ scales were mainly used for pre-school children in Sweden before the introduction of the WPPSI-R. The RCPM and the Griffiths’ developmental quotient give approximations of IQ values. Well-established charts (Spreen and Strauss, 1998) are available and used in clinical practice to get an equivalence of different types of scores and methods. These equations are considered the best possible solution for the categorization of IQ. On the other hand, one advantage in our study was the consensus between the neuropsychologists engaged in the assessments at the different centres.
A secondary aim of this study was to relate surgical complications and histopathological diagnoses to IQ category. The risk of major complications following resective epilepsy surgery was low (2% in the whole series) and in the same order of magnitude in all IQ groups, giving no indication that cognitively disabled patients are at a greater risk to develop major complications. The histopathological diagnoses varied somewhat between the IQ groups, with a slightly higher proportion of cortical malformations in the low IQ groups as expected. Unfortunately, the cases of mesial sclerosis cannot be sorted out from other kinds of gliosis in this series, since mesial sclerosis was first acknowledged as a separate histopathological diagnosis in the register in 1995. The most surprising finding was that there were so few lesional cases in the low IQ groups. The reason for this is not clear, but one might speculate that patients with epilepsy and low IQ to a lesser degree are subjected to neuroradiological investigations as discussed subsequently.
In our study, the issue of post-surgical cognitive vulnerability in low-IQ patients could not be addressed since the Swedish Epilepsy Surgery Register does not contain details concerning cognition, only the categorized IQ data. In order to address this issue, we plan to do a separate follow-up of cognition in the 72 patients with low IQ, together with the respective neuropsychologists who have tested the patients at baseline and at the 2-year follow-up. However, the fear that epilepsy surgery might lead to cognitive deterioration in low IQ patients has not found support in recent studies (Bjornaes et al., 2004; Freitag and Tuxhorn, 2005). Early seizure control by surgical treatment may even lead to a catch-up development in children (Freitag and Tuxhorn, 2005), and several studies report improved alertness and attention after surgery (Olsson et al., 2005; Gleissner et al., 2006).
Patients with cognitive dysfunction often have severe epilepsy but represent a very small proportion of those who receive surgical treatment for their epilepsy, from around 2–3% (US, UK and Germany) to around 15% (Norway, Sweden). The reasons for the low and varying numbers are not clear, but some possibilities can be mentioned. There may be a selection bias due to fear of worse post-operative seizure outcome as well as post-operative cognitive deterioration as discussed earlier. There may also be a referral bias, referring physicians not being aware of the fact that IQ <70 is not today considered to be a contraindication to resective epilepsy surgery. Also, patients with cognitive dysfunction and epilepsy are often not cared for by neurologists or neuropaediatricians, but many other categories of physicians may be involved (Malmgren et al., 2003) and these may not even be aware that the option of epilepsy surgery exists. In our series, patients with lesions did better in all IQ groups than those without lesions, but there were notably fewer lesions in the low-IQ patients. The more favourable outcome in patients with lesions irrespective of IQ level in our series supports the findings of Gleissner et al. who found that 67–78% of patients were seizure-free 1 year after surgery and that seizure outcome did not differ between their three study groups (with IQ <70, IQ 70–84 and IQ >85, respectively). Interestingly, as many as 52% in the IQ <70 group, 58% in the IQ 70–84 group and 48% in the IQ >85 group had a tumour or other lesion, which might be one reason for the favourable seizure outcome (Gleissner et al., 2006). However, if epilepsy surgery is not considered a therapeutic option in the management of patients with epilepsy and low IQ, many cognitively disabled persons might never undergo a neuroradiological investigation in search of an epileptogenic lesion.
Our study is the first that clearly shows that IQ level is an independent predictor of seizure freedom 2 years after resective epilepsy surgery. This should not, however, be taken to indicate that epilepsy surgery is not worthwhile in patients with low IQ. In patients with IQ 50–69 with a baseline seizure frequency of more than 100 per month, it might well be that both the 37% of patients who obtained seizure freedom and the 17% whose seizures were reduced by >75% have gained from surgical treatment of their epilepsy. Even if the seizure free outcome was only 22% in the IQ <50 group, it still indicates that some patients may profit from epilepsy surgery also in this severely disabled group of patients, mainly children.
Seizure frequency should, however, not be the only way of measuring surgical outcome and quality of life questionnaires are part of the follow-up in many epilepsy surgery centres (Vickrey et al., 1995; Malmgren et al., 1997; Wiebe et al., 2001). This might be difficult in cognitively disabled persons and one possibility could be to use special scales that address the concerns of family carers or staff carers. The importance to define the aims for epilepsy surgery has been pointed out by Taylor et al. (2001). In this study a desire for changes in social process (e. g to achieve independence from supervision, and to socialize independently) predominated among the patients’ aims for epilepsy surgery, and in case of cognitive disability changes in behaviour were desired by parents and carers on behalf of the patients. Further studies on the cognitive effects of epilepsy surgery in patients with low IQ are also needed as discussed earlier. Clearly, there is a lack of knowledge of the effects of epilepsy surgery on many aspects of life in patients with epilepsy and low IQ. Addressing these issues is an important challenge, in order to evaluate epilepsy surgery comprehensively in these disabled patients. Such studies are needed before it is possible to make any firm recommendations about which patients with epilepsy and low IQ are likely to benefit from epilepsy surgery.
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Acknowledgements |
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The authors wish to thank the following: all the Swedish epilepsy surgery teams (Lund, Göteborg, Linköping, Stockholm, Uppsala and Umeå); the steering committee of the Swedish National Epilepsy Surgery Register, especially paediatric neuropsychologist Gerd Viggedal; statisticians Nils-Gunnar Pehrsson and Mikael Holtenberg. This work was funded by The Swedish Board of Health and Welfare; The Federation of County Councils; Sahlgrenska Academy at Göteborg University through the LUA-ALF agreement.
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