Cognitive functions, epileptic syndromes and antiepileptic drugs

Some antiepileptic compounds impair learning by rats in a Morris water maze

In the present experiments, we investigated the effects of several commonly employed antiepileptic drugs on the performance of adult rats in a Morris water maze task. We found that phenytoin treatment produced the most deleterious performance impairments across all days of training, and that these performance deficits are not likely due to any general sensorimotor impairments. Carbamazepine had milder, but detectable negative effects, as carbamazepine-treated animals exhibited initial acquisition deficits, but rapidly achieved escape levels comparable to controls. In marked contrast, valproate and ethosuximide had no detectable effects on learning in the water maze. These results parallel previous findings in rats treated with these compounds and tested in an instrumental learning task, and are in general agreement with the human clinical literature. To the extent that one might wish to minimize learning deficits associated with maintenance on antiepileptic drugs, phenytoin is definitely not the treatment of choice, while valproate or ethosuximide are apparently much less disruptive.

Should every child with epilepsy undergo a neuropsychological evaluation?

Neuropsychological (NP) testing has always been an important part of the presurgical workup of patients with epilepsy. Yet, there is no agreement on the timing or circumstances in which NP testing should be ordered in the evaluation of children with epilepsy. This article addresses this controversial question. The early identification of learning or of mental health problems constitutes one of the arguments in support of NP testing. The relative unavailability and high cost of NP testing, the potential inappropriate labeling of children as "learning disabled," and the risk of attached stigma are some of the arguments in support of limiting NP testing to children suspected of having cognitive or behavioral problems. Nevertheless, we concur that at the least, the need for NP testing should be considered by clinicians in the course of their evaluation of every child with epilepsy.

Cognitive side-effects of chronic antiepileptic drug treatment: a review of 25 years of research

Over 90 investigations have been conducted over the past 25 years to determine what effect AEDs have on cognition. No satisfactory answer to this problem can be given, however, chiefly because there is a paucity of studies that pass fairly basic standards of methodology, design and analysis that apply to the evaluation of any clinical research. This severely limits the precision of statements regarding cognitive AED effects. More particularly, there is little reason to recommend any of the first-line AEDs as the AED of choice from the standpoint of cognitive side-effects. On the basis of the present review we are not in a position to provide a straightforward answer to the most pertinent question, i.e., whether AEDs in therapeutic doses have any cognitive effects at all, good or bad. If we reduce the available database to monotherapy studies in epilepsy that use control group data for comparison, employ an appropriate form of repeated measures analysis, and provide sufficient information, very few studies remain that are directly relevant to this issue. This in itself precludes definitive conclusions. As can be seen from Table 9, absolute effects of CBZ and VPA have been examined in epilepsy patients three times each (in four studies), PB has been examined two times, PHT only once. In addition to the paucity of relevant data, there are miscellaneous validity concerns in all of these studies, one recurring theme being that of inconclusive 'no effect' findings with small samples. Without firm knowledge about absolute effects, relative effects, and particularly their absence, are difficult to interpret. Employing the above criteria (except that concerning controls), ten epilepsy studies that address this issue remain (Table 10). It is instructive to look at the number of times particular AEDs have been compared against each other (Table 11). CBZ has been compared to PHT five times, other comparisons occur only once or twice. Again, this is hardly a basis for definitive statements, particularly because validity concerns occur here as well. Recurring concerns here are scattered significant findings that tend to disappear if adjustment of the significance level for multiple comparisons is done, and inconclusive 'no difference' findings with small samples. Even if there were no conclusion validity concerns in individual studies, comparison between studies would be complicated by considerable variation in the subjects studied. Five of the studies summarized in Tables 8 and 9 use children as subject, nine use adults; results obtained in one group may not be generalizable to the other. Also, subjects may be newly diagnosed cases, or patients already on chronic treatment. The latter choice of subjects may be a factor working against detecting cognitive side-effects, as the damage (if any) may already have been done before the beginning of the trial. In addition, a wide variety of assessment tools have been used to search for cognitive effects of AEDs, ranging from measurements of reaction time and motor speed to intelligence tests. Some of these may be more sensitive to drug induced changes in cognition than others. Still, the tentative overall picture emerging from the creme de la creme of research on cognitive AED effects is that differences in cognitive profiles may not be very large. An important point here, of course, is the magnitude of the difference one considers worth detecting. Very few studies have attempted to answer this question. In the majority of studies we examined, a large treatment effect was anticipated implicitly, judging from the generally limited sample sizes. The choice of a study design based on a large treatment effect size may not always be appropriate, though. Of course, one could argue that it is only large effects that may be of practical or clinical significance anyways [30] and that effects of lesser magnitude are of no consequence. However, there are many examples where even a small benefit of one treatme

Epilepsia do lobo temporal: Relato de um paciente intacto após 26 anos de evolução sem tratamento

Apresentamos o caso de um paciente de 36 anos de idade com quadro clínico de epilepsia do lobo temporal, com crises tônico-clônicas desde os 10 anos de idade e parciais complexas desde os 30 anos, que nunca havia recebido tratamento. O diagnóstico foi feito clinicamente e com apoio do eletrencefalograma. A tomografia computadorizada de crânio foi normal. Foi realizado estudo das funções cognitivas com métodos validados em população de pacientes com epilepsia, da mesma origem social e geográfica que o paciente; os resultados foram semelhantes aos obtidos para a população de controle. O paciente também não mostrava alterações aos exames clínico geral, neurológico e das funções mentais. Ele tinha desempenho normal na sociedade, com estrutura familiar estável composta de esposa e filhos, e com emprego estável.

Phenytoin and carbamazepine: differential effects on cognitive function

This review summarizes the studies on the cognitive side-effects of two important antiepileptic drugs: phenytoin and carbamazepine. A large literature database was compiled through the DIMDI computer database and the inspection of recent reviews. Only scientific articles published in peer-reviewed journals during the last 25 years were selected. Of the 358 potentially relevant papers on cognitive effects of AEDs, a total of 16 studies have been found that have studied both carbamazepine and phenytoin. After excluding studies with designs that do not permit valid inferences regarding the cognitive effects of AEDs, only five studies remained. The evaluation of these studies reveal that our current knowledge allows us to draw conclusions about the cognitive side-effects of phenytoin and carbamazepine only with great caution. The claim in reviews that 'both drugs have an impact on cognitive function, PHT to a larger degree than CBZ' is simply not supported by valid 'high quality' data. The same is true for the overall conclusion in more recent reviews that 'drug-induced cognitive effects of these AEDs on cognitive function are probably mild or even negligible'. Apparently, the only information that we have is that the differential impact of PHT and CBZ on cognitive function is not extremely different. No conclusive and reconfirmed data are available on the absolute effects of CBZ and PHT (differences between the two drugs and a no-treatment condition). Our review summarizes some recommendations for future studies.

Vigabatrin: clinical evidence supporting rational polytherapy in management of uncontrolled seizures

Monotherapy is the policy for management of patients with epilepsy. With increasing knowledge of the biology of epilepsy and of the modes of action of antiepileptic drugs (AEDs), this concept must be reevaluated. When monotherapy fails to control seizures, subsequent treatment should be based on "rational pharmacology," taking into consideration the mode of action of the drugs, to provide improved efficacy with maintained tolerance and ease of administration. Introduction of vigabatrin (VGB) as a new AED calls for just such a reevaluation. VGB is an enzyme-activated irreversible inhibitor of gamma-aminobutyric acid (GABA)-transaminase that increases brain and cerebrospinal (CSF) GABA concentrations in animals and humans. It has limited efficacy in the classic animal seizure screening tests, but in many clinical studies has halved the incidence of seizures in approximately 50% of patients, especially those with partial epilepsies. We evaluated the efficacy of VGB in "socially integrated and active outpatients" as a likely subset to demonstrate any advantage of rational polytherapy. The criteria for this evaluation included the effects on seizure frequency, patient tolerability, and cognitive performance in a battery of psychometric tests. Fourteen of the 19 patients (73%) completing the study had > 50% reduction in seizure frequency, and 10 of 19 (52%) had > 70% reduction in seizure frequency. Tolerability appeared good; somnolence was the most frequent adverse event. Three patients complained of a worsening of their seizures, 1 with an increase in frequency and 2 with development of myoclonic jerks not previously reported.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbamazepine and phenytoin in epilepsies refractory to barbiturates: efficacy, toxicity and mental function

A group of 51 patients with chronic cryptogenic or symptomatic localized epilepsy refractory to therapy with barbiturates underwent progressive substitution with phenytoin or carbamazepine, in standardized and randomized fashion. After drug changes were completed two thirds of the patients remained seizure free during a period of 6 months. A clearer effect of phenytoin and carbamazepine was seen on secondary generalized than on partial seizures. The frequency of severe side effects decreased after the change to phenytoin and carbamazepine. The group on carbamazepine improved in immediate and late recall, and in immediate and late recognition of pictures. The group on phenytoin improved significantly in the Stroop test. Patients changed to phenytoin, but not those changed to carbamazepine, became significantly more aggressive, anxious and depressive than when on phenobarbital, as measured by subjective scales. The results indicate that patients should not be considered refractory to antiepileptic drug therapy while on barbiturates. Cognitive dysfunction and mood changes observed in epilepsy may be temporary and dependent on the presence of seizures and/or on use of barbiturates.