Cognitive Skills in Children with Intractable Epilepsy: Comparison of Surgical and Nonsurgical Candidates

Cognitive Skills in Children with Intractable Epilepsy:Comparison of Surgical and Nonsurgical Candidates

*Mary Lou Smith, †Irene M. Elliott, and ‡Lucyna Lach

Departments of *Psychology, †Nursing, ‡Social Work, and Division of Neurology, University of Toronto, and Hospital for SickChildren, Toronto, Ontario, Canada

Summary: Purpose:To compare neuropsychological perfor-mance of two groups of children with intractable epilepsy:those who are surgical candidates, and those who are not.

Methods:Intelligence, verbal memory, visual memory, aca-demic skills, and sustained attention were measured in childrenaged 6–18 years. The effects of number of antiepileptic drugs(AEDs), seizure frequency, age at seizure onset, and duration ofseizure disorder were examined.

Results:Both groups had high rates of impairment. Groupdifferences were found only on the verbal memory task. Chil-dren who experienced seizures in clusters had higher IQ, read-

ing comprehension, and arithmetic scores. Age at seizure onsetand proportion of life with seizures were related to IQ. Perfor-mance did not vary with AED monotherapy versus poly-therapy.

Conclusions:Few differences exist in cognitive performancebetween children with intractable seizures who are and thosewho are not surgical candidates. These findings suggest thatchildren who are not surgical candidates can serve as goodcontrols in studies on cognitive outcome of surgery.KeyWords: Childhood epilepsy—Intelligence—Memory—Attention—Academic skills.

Epilepsy in childhood results in an increased risk forcognitive, behavioral, emotional, psychiatric, and socialimpairments (see 1 for a recent review). These impair-ments occur with higher frequency in epilepsy than inother chronic medical illnesses, highlighting the impor-tance of the underlying neurologic disorder in the etiol-ogy of the deficits (2–4). In the past several decades,epilepsy surgery has increased in prominence as a treat-ment for medically intractable seizures in children andadolescents (hereafter collectively referred to as childrenfor the sake of simplicity). In carefully selected candi-dates, epilepsy surgery can be of benefit by amelioratingor significantly decreasing seizures in 50 to 90% of chil-dren (5–11).

Although the outcome of surgery has been examinedwith respect to its impact on seizure frequency and otherneurologic variables, less is known about the effects onother aspects of the child and his or her development. Ina review of the literature on the effects of surgery onpsychosocial function in individuals younger than 16years, Hermann (12) concluded that the few studies thatexisted had major methodologic flaws, including the lack

of objective standardized measures, poor operationaldefinitions, and anecdotal evidence. He pointed out theneed for prospective studies testing consistent clinicalhypotheses through rigorous methods. In contrast to thestudies of psychosocial function, studies on cognitivefunction have used objective standardized measures, butthey also have been limited by their failure to use anonsurgical control group tested at comparable points intime (13–21). Ten years after Hermann wrote his critiqueof the outcome literature, a review by Strauss andWesterveld (22) again concluded that methodologicallysound studies on psychosocial and cognitive function arelacking, and they pointed out the need for comparisonswith unoperated-on patient control groups.

The choice of a control group for an evaluation of theeffect of surgery is critical but is constrained by a numberof practical factors. Although undoubtedly the best con-trol group would consist of children who are determinedto be good surgical candidates but who do not undergosurgery, it is very difficult to recruit such a group ofpatients. In our experience, very few parents and/or chil-dren refuse the surgical option once it has been decidedthat the child is a good candidate for surgery. Anotheroption might be a wait-list control group, but this groupwould not be suitable for longitudinal studies. In thework described here, we have included, as a comparisongroup, children with medically intractable seizures who

Accepted March 1, 2002.Address correspondence and reprint requests to Dr. M.L. Smith at

Department of Psychology, University of Toronto at Mississauga, 3359Mississauga Road North, Mississauga, ON L5L 1C6, Canada. E-mail:[email protected]

Epilepsia,43(6):631–637, 2002Blackwell Publishing, Inc.© International League Against Epilepsy

631

were evaluated in a tertiary-care epilepsy-monitoringunit, but who were deemed not to be surgical candidates.

The data reported here were collected in the baselinephase of an ongoing prospective longitudinal study of theoutcome of pediatric epilepsy surgery. There are threemain purposes of the initial phase of this study: (a) todescribe the nature and extent of impairment across arange of cognitive variables in children with intractableepilepsy; (b) to determine whether there are similaritiesand differences between children who are deemed to beappropriate surgical candidates and those who are not.This objective will help establish, for future studies inother centers, whether children with nonfocal epilepsiescan serve as appropriate comparison subjects for evalu-ating the short- and long-term effects of surgery. If dif-ferences are found, potential factors related to thesedifferences (e.g., laterality of focus, site of focus) will beexplored; and (c) to gather data with which to comparethe effects of surgery and the effects of potential othermedical variables (such as the effects of the eventualdiscontinuation of medication in those children who doobtain complete seizure relief after surgery).

We report on the first two of these objectives. Intelli-gence, memory, attention, and academic skills were ex-amined in surgical candidates and a comparison group ofchildren with intractable epilepsy. The influence of sei-zure variables and medication on cognitive performancewas also evaluated.

METHODS

SubjectsSubjects were 51 patients recruited through the Epi-

lepsy Monitoring Unit at the Hospital for Sick Childrenin Toronto. All patients were in the Unit for prolongedvideo-EEG recordings lasting from 3 to 5 days for thepurpose of determining the localization and types of sei-zures. In addition to the video-EEG recordings, all sub-jects had clinical neurologic examinations and magneticresonance imaging (MRI) scans. Fourteen children (fivesurgical and nine nonsurgical) had normal MRI scans.Other investigations included positron emission tomog-raphy (PET), single-photon emission computed tomog-raphy (SPECT), subdural grids or strip electrodes, depthelectrodes, and magnetoencephalography (MEG)/magnetic source imaging (MSI), although not all chil-dren underwent each of those procedures. Based on theresults of these investigations, a determination wasmade, by a team of medical experts on epilepsy andepilepsy surgery, whether the child was a surgical can-didate (n4 30) or not (n4 21). Three patients in thesurgical group had had prior epilepsy surgery; one pa-tient in this group had previously had a biopsy [revealinga dysembryoplastic neuroepithelial tumor (DNET)].

Table 1 presents the demographic and seizure-related

characteristics of the two groups. Information on later-ality and site of focus was based on the concordance ofinformation across multiple tests. Further confirmationwithin the surgical group was obtained by intraoperativeand, in the extratemporal cases, extraoperative electro-corticography. Without such information, there may begreater uncertainty with respect to the accuracy of thelocalizing features of the seizures in the control group(23,24); however, in all patients, these variables wereclassified according to the most current results withstate-of-the art investigations. The control group did notinclude any children who had epilepsy syndromes thatwould not be treated with surgery (e.g., Lennox–Gastautsyndrome) or epilepsy associated with neurodegenera-tive disorders (e.g., progressive myoclonic epilepsy).

A review of the seizure history indicated that seizurefrequency varied considerably among the children, andthat, within individuals, seizure frequency varied overtime. In addition, some children had nocturnal seizures,

TABLE 1. Demographic and medical characteristics of thetwo groups

Group

Surgical(n 4 30)

Nonsurgical(n 4 21)

Age (yr)Mean (SD) 13.25 (2.99) 13.02 (3.21)Range 6.33–18.25 7.25–17.75

SexMale 15 11Female 15 10

Full-scale IQMean (SD) 85.07 (17.92) 82.67 (20.34)Range 52–137 46–118

Age at onset of seizures (yr)Mean SD) 6.67 (3.71) 5.38 (4.70)Range 0–14 0–13

Number of AEDs0 0 5%1 27% 19%2 50% 52%3 23% 19%4 0 5%

Laterality of focusLeft 47% 33%Right 53% 10%Othera 0 57%

Site of focusTemporal 60% 24%Frontal 20% 33%Occipital 3% 5%Parietal 3% 0Multilobar/generalized 13% 38%

Seizure frequencyDaily 40% 43%Weekly 20% 24%Monthly 20% 24%Clusteringb 20% 10%

AED, antiepileptic drug.a Includes cases with diffuse bilateral abnormalities, generalized sei-

zures, and independent bilateral focal electrographic abnormalities.b Days to weeks without seizures, then several over 1–2 days.

M. L. SMITH ET AL.632

Epilepsia, Vol. 43, No. 6, 2002

or seizures at school that were not always accuratelyreported. For these reasons, it was not possible to obtainan accurate lifetime estimate of seizure frequency. Astraight count of seizure frequency, even over a shortperiod, may also mask important effects; for example, itmay be that having one seizure per day each week is notthe same as having 6 days free of seizures followed byseven seizures on the next day, even though the seizurefrequency would be the same in both cases. Therefore, ashas been done in other studies (25,26), we developed acategoric classification of seizure frequency. Patientswere placed in one of the following four categories: sei-zures occurring daily (n4 21); seizures not occurringdaily but at least one per week (n4 11); seizures notoccurring every week, but at least once per month (n411); and seizures occurring in clusters (the patient expe-rienced more than two seizures over a 24- to 48-h periodfollowed by intervals of 2 weeks to 3 months with noseizures (n4 8).

All patients in both groups had tried and found unsuc-cessful at least two antiepileptic drugs (AEDs). One childhad tried all conventional AEDs and combinations ofAEDs with no effect on seizure frequency, and thereforewas not taking any medications at the time of the study.Of the remaining 50 participants, 12 children were takingone medication, 26 were taking two medications, 11were taking three medications, and one child was takingfour medications. There were five different single medi-cations, 15 different two-medication combinations, andseven three-medication combinations represented in thissample, making it impossible to examine for specificdrug effects. Instead, we investigated the potential influ-ence of monotherapy versus polytherapy, given thatpolytherapy has been indicated as a risk factor for cog-nitive side effects (27–29).

ProceduresThis study was approved by the Research Ethics

Board (REB) of the Hospital for Sick Children. Informedconsent was obtained from the parents, and informedassent or consent from each of the children, in accor-

dance with the REB guidelines. Each subject was testedindividually by an experienced psychometrician. Mea-sures of intelligence, attention, memory, and academicskills were administered (30–37). Table 2 provides de-tails of the domains, tests, and scores obtained from thesemeasures. The assessment was conducted across two ormore sessions. Breaks were permitted when necessary toavoid fatigue and to accommodate the limited attentionspans of some of the patients. Occasionally a child didnot complete all tests because of time limitations or non-cooperation.

RESULTS

Mean differences were explored with independentgroup t tests or analyses of variance, and categoric datawere examined withx2 tests. When necessary, analyseswere adjusted for heterogeneity of variance. Pearson pro-duct–moment correlations were used to investigate rela-tions between medical and cognitive variables.

Demographic and epilepsy variablesThere were no differences between the groups in age

at the time of the assessment (t49 4 0.26; p < 0.79),Full-Scale IQ (FSIQ; t49 4 0.45; p < 0.66), age at seizureonset (t49 4 1.10; p < 0.27), sex distribution [x2 (1) 40.03; p < 0.86], number of medications [x2 (4) 4 3.28;p < 0.51], or category of seizure frequency [x2 (3) 41.06; p < 0.78]. As would be expected, there was agreater proportion in the nonsurgical group who did nothave lateralized seizures [x2 (2) 4 24.39; p < 0.001].Although there was a higher proportion in the surgicalgroup with a temporal-lobe focus, the distribution of sei-zure foci did not differ significantly between the twogroups [x2 (4) 4 7.52; p < 0.11]. There were no differ-ences in task performance between those children withnormal and those with abnormal MRI findings.

Cognitive variablesThe means for both groups on all tasks, as well as the

number within each group completing each task, are pre-sented in Table 3. Two dependent variables were ana-

TABLE 2. Cognitive domains and measures

Cognitivedomain

Cognitivetest

Dependentmeasures Metric

Intelligence WISC-III (30); WAIS-3 (31) Full-scale IQ (FSIQ), Verbal IQ (VIQ),Performance IQ (PIQ)

Standard scoresa

Academic skills Wechsler Individual Achievement Test (32) Reading decoding, reading comprehension,arithmetic, spelling

Standard scoresa

Verbal memory Children’s Memory Scale (33); DenmanNeuropsychology Memory Scale (34)

Delayed recall of story Scaled scoresb

Visual memory Rey-Osterrieth Complex Figure (35, 36) Delayed recall of geometric design Scaled scoresb

Sustained visualattention

Vigilance and distractibility tasks from GordonDiagnostic System (37)

Number correct and errors of commission Percentile scores

a Standard scores have a mean of 100 and SD of 15 in the general population.b Scaled scores have a mean of 10 and a SD of 3 in the general population.

COGNITIVE SKILLS IN CHILDREN WITH EPILEPSY 633


lyzed for each of the sustained-attention tasks: numbercorrect and errors of commission; the analyses showedthe same pattern of results for both measures, and thusonly the results for number correct are presented in theResults tables. Six children in each of the surgical andnonsurgical groups were unable to comply with the de-mands of the distractibility task, and the test had to bediscontinued for them. Two different measures of de-layed story recall were used, but there was no differencein performance on the two tasks (p > 0.98); therefore theresults across the two tasks were pooled for the analysisto examine group differences. The surgical group per-formed worse than the nonsurgical group at recalling thedetails of a story after a delay. No other group compari-sons were significant.

This finding for story recall was explored further byexamining the potential contributions of variables relat-ing to the site and side of the seizure focus. These analy-ses were done first by pooling the surgical andnonsurgical patients, and second by examination withineach of the surgical and nonsurgical groups. Analyses onsubgroups formed by dividing the patients into thosewith left hemisphere, right hemisphere, and nonlateral-ized foci revealed no differences for either the combinedor separate surgical and nonsurgical groups. When sub-groups were compared on the basis of the site ofdysfunction (temporal only, frontal only, other), no

significant differences emerged for the combined pa-tients or the separate surgical and nonsurgical groups.

Rates of impairmentInspection of the results for the two groups indicated

considerable variability in performance across all mea-sures. For this reason, the data were examined further byestablishing ranges in terms of clinical criteria for per-formance. Scores >−1 SD of the mean for the normalpopulation were classified as “average or above”; scoresbetween 1 and 2 SDs below the mean were classified asrepresenting “mild–moderate impairments”; and scores>2 standard deviations below the mean were consideredto represent “severe impairments.” The percentage ofpatients within each group in each of these performanceranges is presented in Table 4, and potential differenceswere explored by usingx2 analyses. The only variable onwhich the distribution was statistically different betweenthe groups was that of story recall, in which more chil-dren who were surgical candidates showed severe im-pairments [x2 (2) 4 8.21; p < 0.02].

Seizure frequencyThe next question that was addressed was whether

seizure frequency had an impact on the cognitive perfor-mance of these children. The results of the surgical andnonsurgical groups were pooled, and an analysis of vari-ance was conducted to compare each cognitive variable

TABLE 3. Mean performance by both groups across tasks

Measure

Surgical Nonsurgical

t ValueMean (SD) No. Mean (SD) No.

Verbal IQ 88.3 (17.9) 30 87.1 (18.6) 21 0.23, NSPerformance IQ 84.7 (17.5) 30 80.3 (21.7) 21 0.80, NSReading decoding 92.2 (17.2) 29 86.1 (18.5) 20 1.20, NSReading comprehension 90.6 (19.3) 26 91.2 (18.8) 19 −0.09, NSSpelling 91.5 (15.8) 29 86.1 (18.5) 20 1.10, NSArithmetic 83.3 (15.3) 29 79.8 (22.0) 20 0.68, NSStory recall 6.9 (4.4) 29 8.9 (2.4) 21 −2.03, p < 0.05Design recall 6.0 (2.9) 28 6.7 (4.0) 16 −0.68, NSVigilance 39.9 (41.4) 26 44.3 (36.3) 19 −0.38, NSDistractibility 32.9 (26.8) 24 38.5 (35.5) 15 −0.56, NS

TABLE 4. Percentage of subjects in each group in each of the three performance ranges

Measure

Range of performance

x2 Value

Average or above Mild–moderate impairment Severe impairment

Surgical Nonsurgical Surgical Nonsurgical Surgical Nonsurgical

Verbal IQ 63.3 57.1 23.3 28.6 13.3 14.3 0.22, NSPerformance IQ 43.3 42.9 36.7 19.0 20.0 38.1 2.78, NSReading Decoding 72.4 50.0 17.3 30.0 10.3 20.0 2.57, NSReading Comprehension 61.5 57.9 23.1 31.6 15.4 10.5 0.52, NSSpelling 79.3 55.0 10.3 25.0 10.3 20.0 3.33, NSArithmetic 44.8 30.0 37.9 45.0 17.2 25.0 1.17, NSStory Recall 37.9 71.4 24.1 23.8 37.9 4.8 8.72, p < 0.02Design Recall 35.7 50.0 42.9 25.0 21.4 25.0 1.48, NSVigilance 53.8 68.4 30.8 15.8 15.4 15.8 1.39, NSDistractibility 72.7 85.7 18.2 7.2 9.1 7.1 0.98, NS



across the seizure-frequency categories. Because theVerbal and Performance IQ were highly correlated (r40.76; p < 0.001), the composite measure of intellectualfunctioning, FSIQ, was used in this and subsequentanalyses. The results, shown in Table 5, indicate thatseizure frequency had an impact on FSIQ, Reading Com-prehension, and Arithmetic. Post hoc comparisons usingTukey’s test indicated that FSIQ was higher in the pa-tients who had clusters of seizures compared with thosepatients who had seizures on either a daily (p < 0.02) ora weekly basis (p < 0.006). Children with seizures inclusters also had an advantage over those who had sei-zures on a weekly basis in performance on ReadingComprehension (p < 0.04) and Arithmetic (p < 0.03).

Antiepileptic drugsAnalyses of covariance, using seizure frequency as a

covariate, were also conducted to evaluate the potentialimpact of monotherapy versus polytherapy on cognitiveperformance. The one child taking no medication waseliminated from these analyses. No significant differ-ences were found related to number of AEDs.

Age and time variablesCorrelation coefficients were used to investigate the

effects of three other seizure-related variables, age atseizure onset, duration (in years) of epilepsy, and theproportion of the child’s life for which seizures werepresent [calculated as (duration/chronologic age)]. Wechose to examine proportion of life with epilepsy in ad-dition to duration, as the latter can be confounded by thechild’s age. For example, there is potentially a largerdifference in the impact of a seizure disorder of 3 years’duration on a child who is age 4 years compared with oneof age 12 years (the proportion in the former being 0.75and in the latter being 0.25). Age at seizure onset waspositively correlated with FSIQ (r4 0.302; p < 0.03),whereas proportion of life with seizures was negativelycorrelated (r4 –0.301; p < 0.03) with FSIQ. Neither ageat seizure onset nor proportion of life with seizures wascorrelated with any other cognitive variable. Duration of

the seizure disorder did not correlate with any of themeasures.

DISCUSSION

In this study we captured a high rate of cognitiveimpairment among children with intractable epilepsy.Although it is often assumed that the degree of cognitiveimpairment in epilepsy is a consequence of a long-standing history of seizures, these results demonstratethat even children with a relatively short duration canshow considerable impairment in neuropsychologicalfunction.

It also was remarkable that there was a wide range offunctioning within the groups. For example, IQ rangedfrom the Intellectually Deficient (<1st percentile) to theVery Superior (>99th percentile) level. Although theseresults demonstrate that epilepsy does not necessarilyaffect the child’s cognitive function, the risk is very high.Depending on the measure used, 14 to 70% of the chil-dren had an impairment of a mild degree or greater, andthe average rate of impairment across tasks for bothgroups was 45%. This rate is considerably higher thanthat expected in the general population, where∼16% ofchildren would be expected to have impairments of thedegree as defined in our study. All of the children are inschool, and the majority require modifications to accom-modate their cognitive impairments and enhance theirlearning potential. These modifications differ dependingon the school or school district, but encompass a numberof approaches such as special class placement, one-to-one help within the classroom from an educational as-sistant, and curriculum modifications.

Comparability of the groupsThese data were collected in the baseline phase of a

longitudinal study of children undergoing epilepsy sur-gery. At this stage, our purpose was to document thepoints of similarities and differences in the cognitivefunction of children who are surgical candidates andthose who are not. Because of statistical restraints im-

TABLE 5. Cognitive performance in relation to category of seizure frequency

Measure

Seizure frequency

F ValueDaily (n 4 21)

Mean (SD)1–10/wk (n4 11)

Mean (SD)1–10/mo (n4 11)

Mean (SD)Clustering (n4 8)

Mean (SD)

Full-scale IQ 80.3 (17.2) 75.0 (20.7) 86.2 (10.6) 102 (17.3) 4.56, p < 0.007Reading decoding 91.5 (16.3) 82.8 (23.3) 90.3 (16.6) 94.8 (15.7) 1.01, NSReading comprehension 93.1 (18.3) 78.9 (19.0) 90.6 (11.9) 102.9 (22.5) 2.83, p < 0.05Spelling 91.4 (14.0) 82.4 (20.0) 87.8 (13.3) 95.1 (23.3) 1.41, NSArithmetic 80.1 (16.5) 74.7 (21.0) 84.8 (15.7) 94.5 (18.3) 3.02, p < 0.04Story recall 7.5 (3.9) 6.1 (3.1) 8.9 (3.8) 8.9 (4.2) 0.83, NSDesign recall 6.9 (2.9) 5.1 (3.1) 4.8 (3.1) 8.1 (3.5) 2.36, NSVigilance correct 40.3 (36.4) 22.1 (38.5) 54.2 (40.8) 47.4 (41,9) 1.12, NSDistractibility correct 33.1 (33.5) 15.0 (8.4) 39.7 (27.9) 37.3 (31.9) 1.06, NS



posed by our relatively small samples, we had restrictedthe number of measures to include intelligence and thoseareas that have consistently been reported as problematicin children with epilepsy: attention, memory, and aca-demic function. The only measure on which a differencebetween groups was obtained was for the test of delayedstory recall, an index of verbal memory. Analyses wereconducted across all patients and within each of the sur-gical and nonsurgical groups to attempt to identify thevariables that might impinge on this aspect of verbalmemory; however, no differences relating to site (tem-poral, frontal, other), or to laterality (left hemisphere,right hemisphere, or nonlateralized foci) were found.

At first glance it might seem that the lack of relationwith laterality and site may result from small samplesizes once our group is broken down into these dimen-sions, but the finding is consistent with other reports ofmemory in children who undergo surgery. Studies ofpediatric surgical candidates have shown no preoperativedifferences related to laterality on measures of verbalmemory or visual memory (13,15,18,19,21,38). Further-more, Mabbott and Smith (38) found no differences instory recall between children with temporal lobe seizurefoci and those with foci in extratemporal sites. Thus in-tractable seizures in childhood appear not to have spe-cific effects on memory that vary reliably with thelaterality and site of the seizure focus. Such specific ef-fects have been demonstrated, however, in children withmedically controlled seizures (39,40), suggesting that se-verity of the seizure disorder may play a role in theexpression of the memory deficits.

AED findingsThe literature on the effects of AED treatment on cog-

nitive function is characterized by contradictory findingsand methodologic confounds (41–43). Although it hasbeen suggested that polypharmacy may be most detri-mental to cognitive performance (27–29), that relationwas not observed here. However, a wide variety of singleAEDs, combinations of AEDs, and of doses were repre-sented within the sample, and any potential differencesmay have been obscured by these variations and the re-sulting small number of children taking any particulardrug or combination (44). Neurologic factors, such as thepresence of the underlying brain pathology and the rela-tively high frequency of seizures, may outweigh any ad-ditional contribution of taking more than one AED (1). Italso is possible that aspects of neuropsychological func-tion not examined in the present study may be differen-tially affected by number of AEDs. For example, Dodrill(42) suggested that the effects of AEDs are most likely tobe seen on tasks of psychomotor speed.

Timing variablesThe negative impact of seizures on cognitive develop-

ment was seen in the correlation between age at seizure

onset and IQ. The duration of the seizure disorder alsowas found to be negatively correlated with IQ, but onlywhen measured by the proportion of life with seizuresrather than by the total number of years. The formermeasure may take better account of the impact of recur-ring seizures on development.

Seizure frequencyThe adverse effects of epilepsy on cognition in adults

and children has also been documented in the associationbetween seizure frequency and performance on cognitivetasks (26,45–49), although this relation is not alwaysfound (e.g., 25,50). In this study, we demonstrated aneffect not reported before, that children who experiencedtheir seizures in clusters with seizure-free intervals be-tween have an advantage in IQ and certain academicskills (reading comprehension and arithmetic). Theremay be a protective effect of a more prolonged “rest”from seizures that translates into higher functioning inthis group. Although other studies have used a categoricapproach to classifying seizure frequency, none has usedthat of clustering as used here, so this finding awaitsfurther verification in additional and larger samples ofchildren with epilepsy. The results also emphasize thatchildren with reliably chronic and frequent seizures havethe most deleterious outcome with respect to cognition.

Implications of the findingsThe two groups studied here were comparable on a

number of important dimensions: age, sex, age at seizureonset, seizure frequency, and number of medications.The important finding in this study is the high degree ofsimilarity between the surgical and nonsurgical groups intheir cognitive performance. The Pediatric Surgery Com-mission of the International League Against Epilepsyrecently emphasized the lack of outcome studies on sur-gery and cognition in children (51). Our experience dem-onstrates the feasibility of recruiting a comparison groupof children with intractable epilepsy for the purpose ofconducting prospective outcome research on the effectsof epilepsy surgery.

Acknowledgment: This research was assisted by the On-tario Mental Health Foundation. We thank Dr. Mary Desrocherand Shameela Hoosen-Shakeel for their assistance in testing thepatients, and Nicholas Blanchette and Darren Kadis for helpwith the data analysis. We are grateful to Drs. William Logan,J. Rutka, O. C. Snead III, and S. Weiss for the opportunity tostudy their patients. Finally, we thank all the children, teenag-ers, and their parents who generously gave of their time toparticipate in this study.

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Cognitive Skills in Children with Intractable Epilepsy: Comparison of Surgical and Nonsurgical Candidates