Neuropsychology in epilepsy: Children are not small adults

One of the many remarkable aspects of Fred and Eva Andermann's careers is their interest in epilepsy across the life span. Just as there are differing diagnostic considerations from the perspective of the neurologist and neurogeneticist between epilepsies with onset in childhood and adulthood, the neuropsychology of epilepsy differs across age. The impact of seizures and their underlying abnormal neural substrate are different in the developing and the mature brain. In children, epilepsy occurs within a more dynamic nervous system and the neuropsychological implications reflect ongoing maturational changes, plasticity at the behavioral and structural level, and the impact of environmental and social factors on development (Fletcher & Taylor, 1984). In the adult, the conditions leading to or arising from epilepsy may result in a loss or interference with previously acquired functions. In contrast, in a child, there may be interference with development rather than a striking loss of function. This interference may affect eventual outcome in a number of ways: A child may fail to develop a skill, no longer progressing normally along the developmental continuum; the child may have a slowed rate of development in acquiring a behavior; or the child may actually regress or lose previously acquired developmental skills. In children, the time from insult to behavioral expression may be lengthy; the first two possible patterns may not be clinically manifested until the child must engage in a behavior that depends on the affected neurologic substrate. For example, injury to prefrontal regions may not be expressed until those brain systems are in ascendancy, in later childhood or adolescence. Patients with seizure onset in childhood experience pathology at an early stage of development. This timing in some instances may lead to greater neurologic compromise and may be accompanied by widespread and more severe neuropsychological compromise than is found in adult-onset seizures. In our work with children with intractable epilepsy, we have typically found that there is less specificity in the cognitive manifestations of focal seizures than is seen in adults; therefore, for example, we often do not find the same kind of differences in memory relating to the site of laterality of the seizure focus (Hepworth & Smith, 2002; Smith et al., 2002, 2004). Figure 1 shows that children with unilateral seizure foci in the frontal or temporal lobe do not differ on measures of verbal (delayed recall of a list of words) or visual (recognition of unfamiliar faces) memory; in addition, no differences were found related to the laterality of the focus. Performance of children with temporal or frontal lobe seizures on measures of face recognition and recall of a list of words. No differences were found relating to site or to laterality of seizure focus. One study that clearly illustrates the difference between the neuropsychological manifestations of early versus later onset epilepsy is that of Hermann et al. (2002), who compared neuropsychological and volumetric magnetic resonance imaging (MRI) measures in two groups of adults with temporal lobe epilepsy. One group had a mean age of seizure onset at 7.8 years of age, and the other at 23 years of age. The analyses were carefully controlled for duration of epilepsy, presence of initial precipitating injury, secondary generalized epilepsy, depression, comorbid medical disorders, duration of epilepsy, and number of anticonvulsant medications, but nonetheless showed striking differences between the groups. The early-onset patients performed more poorly on all cognitive measures (intelligence, language, visual perception, memory, and executive function) compared with controls and late-onset patients, whereas few differences were found between the late-onset patients and controls. The early-onset group had reduced total brain and white matter volume, whereas the late-onset group did not differ from controls. A difference in white matter volume was also found between the two patient groups, and these differences remained significant after controlling for duration of epilepsy. In the early-onset group, the reductions in brain tissue volume were not limited to the temporal lobe, and were seen both ipsilateral and contralateral to the side of seizure onset. There may, however, be some advantages associated with epilepsy in the younger brain. Earlier seizure onset may permit a redistribution of function to other brain areas, leading to fewer deficits after surgery. Gleissner et al. (2005) studied memory outcomes in 30 pairs of patients (one child and one adult within each pair) matched for age of onset, sex, number of seizures, seizure types, side of surgery, and type of temporal lobe resection. Three months after surgery, left-resected groups showed a significant decrease in verbal learning; by 1 year, however, the children, but not the adults, had recovered to their preoperative baseline. The authors hypothesized that the recovery in children was due to plasticity in the immature brain. One lesson learned in the field of developmental neuropsychology is that the brain-behavior rules derived from the study of adults do not necessarily apply to children. This lesson is well illustrated by the contrasting patterns of neuropsychological performance in children and adults with epilepsy. It is also important to be aware that developmental change may result in the emergence of different patterns of strengths and weaknesses in the child's cognitive abilities over time. Expectations for typical patterns and timing of developmental change may also need to be adjusted to account for the potential influence of changes in seizure status or treatments. The author has no conflict of interest to disclose.

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