Consequences of antiepileptic drug withdrawal: A randomized, double-blind study (Akershus Study)

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1 FULL-LENGTH ORIGINAL RESEARCH Consequences of antiepileptic drug withdrawal: A randomized, double-blind study (Akershus Study) Morten Ingvar Lossius, Erik Hessen, Petter Mowinckel, Knut Stavem, Jan Erikssen,, Paal Gulbrandsen, and, Leif Gjerstad Helse Øst Health Services Research Centre, Akershus University Hospital, Lorenskog, Norway; National Centre for Epilepsy, Division for Clinical Neuroscience, Rikshospitalet-Medical Centre, Oslo, Norway; Department of Neurology, Akershus University Hospital, Lorenskog, Norway; Department of Paediatrics, Division Woman and Child, Ullevål University Hospital, Oslo, Norway; Department of Medicine, Akershus University Hospital, Lorenskog, Norway; Department of Preventive Medicine, Akershus University Hospital, Lorenskog, Norway; Department of Neurology, Division for Clinical Neuroscience, Rikshospitalet Medical Centre, Oslo, Norway; and Faculty of Medicine, University of Oslo, Norway SUMMARY Objective: Despite side effects associated with the use of antiepileptic drugs (AEDs), withdrawal of AEDs remains controversial, even after prolonged seizure freedom. The main objective of this study was to assess the effects of AED withdrawal on cognitive functions, seizure relapse, health-related quality of life (HRQOL), and EEG results. Additionally, potential predictors for freedom from seizures after AED withdrawal were studied. Methods: Patients, seizure-free for more than 2 years on AED monotherapy, were recruited for a controlled, prospective, randomized, doubleblinded withdrawal study lasting for 12 months, or until seizure relapse. Patients were randomized to AED withdrawal (n = 79) and nonwithdrawal (n = 81) groups. The examination program included clinical neurological examinations, neuropsychological testing, EEG-recordings, cerebral MRI, and assessments of HRQOL. Follow-up data on seizure relapse were also collected beyond the 12-month study period (median 47 months). Results: Seizure relapse at 12 months occurred in 15% of the withdrawal group and 7% of the nonwithdrawal group (RR 2.46; 95% CI: ; p = 0.095). After withdrawal, seizure relapse rates were 27% after a median of 41 months off medication. A normal result to all 15 neuropsychological tests increased significantly from 11% to 28% postwithdrawal. We found no significant effects of withdrawal on quality of life and EEG. Predictors for remaining seizure-free after AED-withdrawal over 1 year were normal neurological examination and use of carbamazepine prior to withdrawal. Conclusion: Seizure-free epilepsy patients on AED monotherapy who taper their medication may improve neuropsychological performance with a relative risk of seizure relapse of 2.46, compared to those continuing therapy. KEY WORDS: RCT, Epilepsy, Withdrawal of antiepileptic drugs, Cognition, HRQOL, EEG, Seizure relapse. Approximately 70% of patients with recent onset epilepsy become seizure-free on antiepileptic drugs Accepted August 15, 2007; Online Early publication September 24, Address correspondence and reprint requests to Morten Ingvar Lossius National Centre for Epilepsy, P.O. Box 53, 1306 Baerum postterminal, Norway. Morten.lossius@epilepsy.no Blackwell Publishing, Inc. C 2008 International League Against Epilepsy (AEDs) (Kwan and Brodie, 2000), although many of them experience different drug side effects, some of which are serious (Specchio and Beghi, 2004). Reduced attention, mental speed, psychomotor slowing, and impaired memory (Vermeulen and Aldenkamp, 1995) are subtle side effects, with the potential to create problems during activities at work and in daily life. Despite the favorable reaction of side effects to AED withdrawal, this procedure remains controversial, even in persons with prolonged seizure freedom, because of the fear of provoking seizure relapse. 455

2 456 M. I. Lossius et al. So far withdrawal studies have been open, and have included a broad spectrum of epilepsy patients, on both mono and poly AED therapy (Overweg et al., 1987; Callaghan et al., 1988; Medical Research Council Antiepileptic Drug Withdrawal Study, 1991; Specchio et al, 2002). The MRC AED Withdrawal study assessed the risk benefit aspects of AED withdrawal in a broad sense and found no net gain in terms of overall quality of life for either treatment policy. The findings suggested however, that patients with low relapse risk may derive considerable psychosocial benefits from discontinuation of AED therapy (Jacoby et al., 1992). The risk-benefit aspect of AED withdrawal, in particularly the neuropschychological effects, has not been fully explored as this information can best be obtained through prospective, randomized, double-blind trials among seizure-free patients. Our primary aim was to conduct such a study, assessing effects of AED withdrawal on seizure relapse rate and possible changes in cognitive functions. Secondarily, we wanted to study possible effects on health related quality of life (HRQOL), and EEGfindings. In brief: Which beneficial effects can be offered by AED-withdrawal and at what risk? METHODS Sample size The anticipation of a difference in seizure relapse rates between the withdrawal and nonwithdrawal arms of the study enabled us to minimize the study population for ethical reasons. With this in mind, and in the absence of guidelines on what constitutes a significant change in neuropsychological scores, it was decided that a 0.5 standard deviation change in neuropsychological scores would probably be of clinical interest. Based on a Type I error of 0.05 and a Type II error of 0.90, 170 patients would be needed for the study, while a Type II error of 0.80 would require 138 patients. After discussions with our Ethical Committee, it was decided to include between 160 and 180 patients, anticipating a dropout rate of about 10%. Safety evaluation Our legal adviser formulated a legal document referring to possible claims arising from injuries connected to an epileptic seizure, and also clarifying the responsibilities of the Institute. To increase patient safety further, two sets of coded envelopes were made, one of which was kept in the patient record and the other given to each patient, for use in cases of emergency when it might be important to know whether a patient was on drug therapy or placebo. Envelopes were to be kept sealed and unopened until study termination (to be opened if seizures occurred) when they were to be returned. Given the adverse effects of AEDs we cannot rule out that some patients may have been aware of the treatment policy but this was not systematically assessed. Table 1. Inclusion and exclusion criteria Inclusion criteria: Epilepsy (at least two unprovoked seizures) Two years seizure freedom or longer Monotherapy Age: years If prior withdrawal attempted and unsuccessful, five years seizure freedom or longer is needed Exclusion criteria: Juvenile myoclonic epilepsy (JME) Polytherapy Paroxysmal epileptiform activity in patients with primarily generalized epilepsy Two prior withdrawal attempts Pregnant or seeking pregnancy Mental retardation Progressive neurological disease Other serious disease which may influence the health status of the patient in the study period Comedication (except postmenopausal hormone substitution, hormonal contraceptives, acetylic acid, antihypertensiva and thyroxin) The Regional Committee for Medical Research Ethics approved the study protocol (Approval S-127/ ). Patients Patients were selected from the epilepsy registries of our hospital and six neurological outpatient clinics in the Oslo area. Inclusion was stopped when 168 had given their informed, written consent to participate. Table 1 lists the inclusion criteria. Figure 1 indicates how the 241 patients, assessed for eligibility, were reduced to 160 who were finally included for randomization (79 to withdrawal and 81 to continued medication). None of the patients included had had epilepsy surgery. In the period between randomization and the start of the intervention, six patients withdrew themselves, two had generalized epileptic discharges on EEG, one experienced seizures while still on his AED, and one suffered a subarachnoid hemorrhage. Thus, 150 patients were included in the intervention part of the study (78 in the nonwithdrawal and 72 in the withdrawal group). Due to protocol violation, one patient was excluded from the analyses. Inclusion started in October 1999 and ended in March Design The study followed a prospective, randomized controlled, double-blind design. Patients came for five visits over a 12-month period, or until seizure relapse. Those experiencing seizure relapse or serious diseases, mandating code breaking, received appropriate treatment. All those randomized to the nonwithdrawal group were offered AED-withdrawal, controlled by the primary investigator, after study termination.

3 457 Akershus Double-blinded AED Withdrawal Study Figure 1. Patient flowchart (adpt. from The consort E-Flowchart Aug 2005) Epilepsia C ILAE Randomization The patients were randomized in blocks of 10, between visit one and visit two, to receive blindly active medication or placebo in prepacked dispensers (dosett, Item Development AB, Stocksund, Sweden), one for each of the 12 withdrawal weeks. Those randomized to withdrawal had AED dose reduction by 20% of the initial dose in the first 6 weeks and 20% of the initial dose every second week over the following weeks. The reduced medication was substituted with placebo to keep the study double-blinded. Survey examination program (5 visits) 1. Interview, neurological examination (MIL), neuropsychological testing (EH), EEG, cerebral MRI, HRQOL, ECG, and fasting blood samples. 2. (At one month); intervention started (tablet supply). 3. (At three months); clinical control visit (tablet supply). 4. (At seven months); repeat of all investigations performed at visit 1, except MRI. 5. (At 12 months); study terminated, code-breaking. Further follow-up In September 2006, we collected additional follow-up data on medication and seizures for all but three patients, who could not be reached despite extensive efforts. Since the study period, four patients had died; two of serious somatic disease not connected to epilepsy and two were apparently sudden unexpected death in epilepsy. Of these, one died only a few weeks after withdrawal and one died 4 years after withdrawal.

4 458 M. I. Lossius et al. Median follow-up was 47 months, and 41 months for patients off medication. Neuropsychology 15 tests were applied: 1 2: Immediate verbal and visual memory (Rey, 1964; Wechsler, 1987; Schmidt, 1996). 3 4: Delayed verbal and visual memory (30 minutes) (Rey, 1964; Wechsler, 1987; Schmidt, 1996). 5 6: Attention and psychomotor speed (Lewis and Rennick, 1979; Reitan and Wolfson, 1985). 7 9: Executive functions like verbal fluency, response inhibition, and divided attention (Lewis and Rennick, 1979; Benton and Hamsher, 1989; Trennery et al., 1989) : Simple reaction time with both hands and choice reaction time with lexical and figurative stimuli (Miller, 1990) : Motor speed and complex coordination with both hands (Kløve, 1963). All tests have previously been validated thoroughly, and for all tests normative data are defined (Kløve, 1963; Miller, 1990; Heaton et al., 1991). When differentiating between normal and abnormal test scores, a T-score >39 was used as normal (Heaton et al., 1991). A sum score was created, based on the proportion of patients scoring normal on all 15 tests before and after intervention. EEG recordings EEGs were recorded according to international electrode placement system (16 channels). The EEG variables registered were: epileptiform activity, focal epileptiform activity, generalized epileptiform activity, abnormal activity others than epileptiform. Quality of life For assessment of HRQOL, we used the validated Norwegian version of the disease-specific Quality of Life in Epilepsy Inventory (QOLIE-89, version 1) (Vickrey et al., 1993; Stavem et al., 2000), the generic EQ-5D including a 20 cm visual analog scale (EQ-VAS) (The EuroQol Group, 1990), and the 15D questionnaire (Sintonen, 1994a; Sintonen, 1994b; Stavem et al., 2001). Questionnaire scoring followed defined procedures (The EuroQol Group, 1990; Sintonen, 1994b; Stavem et al., 2001). Statistical analysis The primary outcomes were seizure relapse and changes in cognitive function. Secondary outcomes were changes in HRQOL and EEG. Seizure relapse was assed continually and cognitive function, HRQOL and EEG were assessed at inclusion and 7 months after intervention started, that is, 8 months after inclusion and 4 months after end of withdrawal. Student s t-test and chi-square test were used for testing group differences for continuous and categorical variables, respectively. For occurrence of seizures, a Kaplan Meier curve with log-rank test was used. Intention to treat analyses was performed. Odds ratios for seizure relapse were estimated with logistic regression analyses. To assess possible predictors for seizure relapse in the withdrawal group, we tested variables of importance in logistic bivariate models. The independent variables were carbamazepine (CBZ) versus other medications, normal neurological examination versus abnormal, partial versus generalized epilepsy, age, gender, duration of seizure freedom, MRI pathology versus no pathology, and age at epilepsy onset. Since only 11 events (seizure relapse) occurred among those who had withdrawn AEDs, the number of variables in the multivariate logistic model was limited to two (neurological examination that is no sensory, motor, or cranial nerve deficits, and type of medication). We calculated the overall risk for seizure relapse after withdrawal based on a total of patients that had ended medication both within the study period (12 months) and at study termination (median follow-up 47 months). All reported p-values were 2-sided and not adjusted for multiple testing. No interim analysis was scheduled or performed. Statistical analyses were performed using SPSS, version 14. RESULTS Among those who were found to fulfill the inclusion/exclusion criteria, but chose not participate (n = 28), 13 were women (46%), and mean age was 38 years (range: years). There were no significant differences between the withdrawal and nonwithdrawal groups for the following baseline variables: age, gender, epilepsy onset, duration of freedom from seizures, seizure type, MRI pathology, etiology, epileptic activity on the EEG, serum concentration of AED within therapeutic range, and medication (Table 2). Seizure relapse Within 12 months, five of the 77 nonwithdrawers (7%) and 11 of the 72 withdrawers (15%) had experienced seizure relapse (RR 2.46; 95% CI: ; p = 0.095) (Figure 2). The seizures caused no serious harm to the patients in the study period (12 months). One of the 11 experiencing seizure relapse in the withdrawal group, had a seizure provoked by extreme physical exertion after discontinuing CBZ-therapy. He refused to restart medication. The intention-to-treat analyses showed no significant effects on the estimates. At termination of the double-blind period (12 months), 64 of the 72 patients in the nonwithdrawal group (those that had not experienced seizure relapse during the study) decided to taper their AEDs (i.e., eight chose to remain on

5 459 Akershus Double-blinded AED Withdrawal Study Table 2. Baseline characteristics of study patients No withdrawal (n = 78) Withdrawal (n = 72) p-values Mean age (range) 37 (18 66) 40 (19 65) Female (percent) 39 (50) 41 (57) 0.39 Epilepsy onset; no. of patients (percent) 0 11 years 10 (13) 4 (6) years 22 (28) 22 (31) years 46 (59) 46 (64) Seizure-free; no. of patients (percent) 2 3 years 3 (4) 6 (8) years 20 (26) 21 (29) >5 years 55 (71) 45 (63) Epilepsy type; no. of patients (percent) Localization related 59 (76) 55 (76) 0.39 Generalized 17 (22) 17 (24) Unclassified 2 (3) 0 Seizure type; no. of patients (percent) Partial epilepsy Secondarily generalized tonic clonic seizures 52 (68) 44 (61) 0.49 Complex partial seizures 19 (25) 26 (36) 0.15 Simple partial seizures 19 (25) 17 (24) 1.00 Unclassified seizures 0 1 (1) 0.48 Generalized epilepsy Primarily generalized tonic clonic seizures 14 (18) 16 (22) 0.55 Absences 1 (1) 1 (1) 1.00 Other 1(1) 1 (1) 1.00 No. of patients (percent) Normal neurological status 72 (92) 68 (94) 0.60 MRI pathology 21 (28) 16 (23) 0.45 Known etiology 23 (30) 20 (28) 0.82 Epileptic activity on the EEG 35 (45) 25 (34) 0.13 Serum concentration in therapeutic range 63 (81) 55 (76) 0.51 Medication; no. of patients (percent) Carbamazepine 52 (67) 41 (57) 0.22 Valproate 18 (23) 15 (21) 0.74 Phenytoin 5 (6) 8 (11) 0.30 Phenobarbital 2 (3) 3 (4) NA Lamotrigine 1 (1) 5 (7) NA NA = not applicable. medication). Four of 61 in the intervention group (11 had seizure relapse in the randomized controlled trial (RCT) and one patient was not applicable for follow-up) chose, despite no seizure relapse, to recommence their AEDs. The 1-year risk of seizure relapse among the 60 patients in the nonwithdrawal group, who then stopped their AEDmedication subsequent to the double-blind period, was similar to that observed in the intervention group during the first year (Figure 2). Eleven patients experienced seizure relapse after withdrawal in the nonwithdrawal group 1 year after withdrawal started after study termination, that is, 9 months after end of withdrawal. Among the combined group of patients who tapered their AEDs with a median follow-up of 41 months off medication, we found a declining monthly risk of seizures from (95% CI: ) immediately after tapering to (95% CI: ) at 6 months, (95% CI: ) at 12 months, (95% CI: ) at 24 months, and (95% CI: ) at 36 months. Neuropsychological findings Improvement in neuropsychological function from first to second assessment (4 months after end of withdrawal) was evident for all tests in both groups. Apart from for two tests, the improvement was greater in the withdrawal group than in the nonwithdrawal group. Table 3 shows the five tests with significant differences between the groups; verbal fluency under time pressure, complex motor coordination with nondominant hand, response inhibition under time pressure, choice reaction time with lexical stimuli, and form discrimination. Further details on the two latter have now been published (Hessen et al., 2006). A normal result to all 15 tests increased from 11% to 28% postwithdrawal (Table 3) contrasting with a decrease in the proportion of normal results for all tests, from 11% to 9%, in the nonwithdrawal group (Table 3). The beneficial effect was similar in all age groups, but significantly better in patients with serum CBZ-values above median compared to those below median (p = 0.03). A more

6 460 M. I. Lossius et al. Figure 2. Seizure relapse in the two randomized groups of AED withdrawal ( ) and nonwithdrawal ( ) in the study period (12 months), and open follow-up (all patients off medication) Epilepsia C ILAE detailed presentation on neuropsychological effects of AEDs has been published (Hessen et al., 2007). Quality of life No significant group differences were observed (Table 3). EEG-findings Abnormal EEG-findings (including epileptiform activity) at baseline and at test 2 remained insignificantly different in the two groups (Table 3). Predictors of freedom from seizures Bivariate logistic analysis demonstrated that neither patient age, gender, age of epilepsy onset, partial versus generalized epilepsy, MRI-findings, nor duration of seizure freedom predicted seizure freedom after AED withdrawal. Three of those who had seizure relapse in the withdrawal group had used CBZ, compared with eight on other medications. In a multivariate logistic analysis, this gave an odds ratio of 6.33 (95% CI: ) of remaining seizurefree for 1 year, when prior use of CBZ was compared with prior use of any other AED. At a median of 41 months, patients on CBZ had an almost threefold chance of remaining seizure-free after withdrawal, compared with patients on any other AED (OR 2.86; 95% CI: ; p = 0.01). A normal neurological examination was also a significant predictor (multivariate analysis) for seizure freedom at 12 months (OR 2.77; 95% CI: ; p = 0.036). DISCUSSION The study described here used a double-blind, randomized comparison of consequences of AED-withdrawal versus nonwithdrawal, to enable an assessment of the advantages/disadvantages of AED-withdrawal. We observed an increase in seizure relapse rate among withdrawers at 12 months, and if all the data are considered, the relative risk may be more than doubled. At two years, 81% of the withdrawers from the RCT remained seizure-free, i.e. a relapse rate of 19%. Three more patients had seizure relapse within 12 months after study termination in the withdrawal group. The declining monthly risk of

7 461 Akershus Double-blinded AED Withdrawal Study Table 3. Changes in main outcome measures recorded before and seven months after intervention No withdrawal Withdrawal Mean difference Before After Before After in changes between n intervention intervention n intervention intervention the two groups (CI) p-values Neuropsychological parameters No. of patients with all 74 9 (11) 7 (9) 64 8 (11) 18 (28) NA <0.005 b normal neuropsychological tests (percent) Raw scores of: FAS-Word fluency (13.3) 35.6 (13.1) (10.8) 39.2 (13.6) 3.51 ( ) a (words) mean (SD) Stroop Color Word (17.6) (15) (18.8) (15.2) 3.63 ( ) a (words) mean (SD) Motor test, (11.7) 69.4 (10.8) (13.7) 69.2 (12.7) 3.66 ( 6.64 to 0.68) a nondominant hand (secs) mean (SD) Choice reaction (81.0) (85.8) (84.2) (71.5) ( to 8.74) a time-lexical (ms) mean (SD) c Form Discrimination (161.1) (148.5) (163.4) (151.0) ( to 9.14) a (ms) mean (SD) c Quality of life parameters QOLIE-89 overall (6.4) 60.9 (6.2) (6.8) 59.8 (6.4) 0.3 ( 1.55 to 2.07) 0.78 a score mean (SD) 15D utility score (0.07) 0.94 (0.07) (0.07) 0.93 (0.05) ( to 0.005) 0.22 a mean (SD) EQ visual analog scale (13.3) 78.5 (15.6) (13.1) 83.0 (10.5) 3.03 ( 0.99 to 7.06) 0.14 a mean (SD) EEG-findings; no. of patients (percent) Abnormal EEG (73) 51 (69) (55) 37 (60) NA 0.64 b Epileptiform activity on EEG (45) 34 (47) (30) 19 (31) NA 0.28 b a t-test b chi-square test c published elsewhere; NA, not applicable. seizures in the combined group further underlines that most patients will experience seizures after withdrawal within the first six to nine months after ended discontinuation. Although one of the inclusion criterions was a minimum of 2 years free of seizures, 67% of the study patients had bee seizure-free for more than five years. This may have increased the likelihood of remaining seizure-free. The MRC Antiepileptic Drug Withdrawal Study Group (1991) reported a two-year relapse rate of 22% among nonwithdrawers, compared to 41% among withdrawers. The marked difference in relapse rate between the two studies is probably due to different inclusion criteria in the two studies. The MRC study included a broad spectrum of patients, also including some on AED polytherapy. Our inclusion criteria may have been strict, but a large proportion of epilepsy patients are seizure-free and on monotherapy (Kwan and Brodie, 2000). We observed a declining risk of seizure relapse over time after withdrawal. This is probably due to continuous selection of those least likely to have seizures. A modest, but general, improvement in neuropsychological function was demonstrated among those who had withdrawn AEDs. The favorable results among those with higher, versus lower, CBZ serum values support this observation. The findings indicate that AEDs have a modest, but reversible, depressing effect on some cognitive functions and complex motor coordination. The practice effect might have meant that greater cognitive improvement due to AED withdrawal could not be observed. The effects on patients who abstain from AEDs for a more prolonged period remain to be seen. Our results differ from those reported in two previous studies on neuropsychological consequences of CBZ in healthy volunteers and epilepsy patients (Thompson et al., 1980; Aldenkamp et al., 1993), and from those in a comparative study of CBZ and valproate (Prevey et al., 1996). However, our data are in close agreement with those of Meador et al. (1991 and 1993), who showed improved concentration and memory following AED withdrawal. The implications that these changes in neuropsychological functions may have on daily life remain unknown, however it seems probable that the ability to perform activities that demand rapid cognitive performance and

8 462 M. I. Lossius et al. complex motor coordination may be improved after AED withdrawal. Despite improvement in neuropsychological performance, no improvement in HRQOL was observed after AED withdrawal. Adaptation to a new steady state of health (or ill-health) may be reported as no change, if measurement is made after a prolonged drug-free period. The double-blinded design excludes one known positive effect of being off medication; namely not having to take drugs regularly. Fear of seizure relapse due to patients being blinded would be expected to have a negative impact on HRQOL. Both the neuropsychological and HRQOL results may be influenced by the relative short period (four months after the end of the withdrawal period (three months) to the second investigation. The Medical Research Council (MRC) Drug Withdrawal Group suggested that open AED-withdrawal was associated with an improved (although statistically nonsignificant) feeling of well-being (Jacoby et al., 1992). The overall effects on quality of life associated with AEDwithdrawal remain unresolved. Both at baseline and during follow-up, EEG-findings were without prognostic information on seizure relapse among both those who had withdrawn and those who had not withdrawn AEDs. Since as many as 31% of those who had withdrawn AEDs had epileptic discharges at baseline, and 30% at test 2, the prognostic role of abnormal and epileptiform discharges in EEG of adults with known epilepsy is not fully understood. Although the prognostic significance of EEG pathology at drug withdrawal in children seems undisputed (Specchio and Beghi, 2004), the value of EEG in predicting outcome after withdrawal in adults is controversial (Specchio and Beghi, 2004). Some studies in adults (Callaghan et al., 1988; Specchio et al., 2002) showed an increased risk of relapse in patients with EEG abnormalities in bivariate analysis, but not in multivariate analysis. We are not aware of studies in adults, using multivariate analysis, which report any significant predictive value of EEG abnormalities prior to withdrawal. Reliable predictors for remaining seizure-free after discontinuation of AEDs in adults have been difficult to find. However, multiple AEDs (Medical Research Council Antiepileptic Drug Withdrawal Study Group, 1991 and 1993), adolescent or adult onset epilepsy (Callaghan et al., 1988), an underlying cerebral substrate (Specchio et al., 2002), partial seizures (Specchio et al., 2002), specific AEDs used prior to withdrawal (Medical Research Council Antiepileptic Drug Withdrawal Study Group, 1993), and epilepsy syndromes with high potential for seizure relapse (e.g., juvenile myoclonic epilepsy) (Specchio and Beghi, 2004) are claimed to be negative predictors for remaining seizure-free after withdrawal. We found normal neurological examination and CBZ use prior to withdrawal to be significant positive predictors for remaining seizure-free after AED-withdrawal at 12 months, and the latter also at 41 months (median). The positive effect of CBZ use prior to withdrawal was also reported in the MRC study (Chadwick, 1999) who found that patients on CBZ-monotherapy would be less likely to have a relapse after withdrawal, than patients stopping treatment with any other AEDs. Since CBZ is the first-line treatment in partial epilepsy, patients demonstrating a good response to CBZ probably have easy-to-treat epilepsy although we were unable to find significant data in our study to confirm that the CBZ treated patients had a more benign epilepsy than those treated with other AEDs (data not shown). We still have no evidence to suggest that the observation should be attributed to particular, intrinsic properties of CBZ. The withdrawal of AED therapy must always be discussed thoroughly with the patient. Most seizures will occur during the first 6 months after withdrawal, and if a seizure does not occur in this period, then the risk after 1 year is almost the same as if AED use had continued (i.e., nonwithdrawal). If CBZ is the AED in use, or if the patient considering withdrawal has normal neurological status, it should be noted that these factors are associated with lower risk of seizure relapse following AED withdrawal. Furthermore, the likely effects of AED withdrawal on neuropsychological functions should be provided in as much detail as possible, whilst ensuring that the patient understands that changes in the quality of life may be modest, at least initially. However, the study described here demonstrates that for the majority of patients with significant predictors for remaining seizure-free after AED withdrawal, controlled AED withdrawal may have beneficial effects. ACKNOWLEDGMENTS We would like to thank all the patients who, without any compensation, visited the hospital seven times and spent many hours there due undergoing extensive testing and examinations, despite being busy at work or in education. We also wish to thank the following colleagues: Kari- Anne Huuser, Gunhild Hammarstrøm, Bjørn Guldvog, Dag Hofoss, Ole Morten Rønning, Saga Høgheim, Karl Otto Nakken, Leiv Sandvik, and Kari Mette Lillestølen. The study received financial support from: The Norwegian Foundation for Health and Rehabilitation (EXTRA FUND), The Norwegian Epilepsy Association, and The Norwegian Chapter of the International League Against Epilepsy. The various active drugs and placebo tablets were provided from The Pharmacy in Krageroe (Norway), GlaxoSmithKline, Desitin, and Novartis. Conflict of interest: The authors reported no conflicts of interest. 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