Epilepsy and child development

The complex relationship between epilepsy, language, behaviour and cognition is not well understood. However, epidemiological studies have consistently suggested a link between epilepsy and cognitive and behavioural impairments. The UK child health and education survey followed a cohort of over 16000 children bom in a particular week in 1970. After follow-up for 10 years, 30% o f the children with epilepsy were reported to have a developmental delay or disability, a figure that rose to 73% for children with symptomatic seizures (Verity, et al., 1992). McDermott and colleagues (1995) carried out a population-based study o f behaviour problems in US children using data from the 1988 National Health Interview Survey. They found that children with parent-reported seizures were 4.7 times more likely to have behaviour problems than controls. In addition, 21.5% were classified as having a developmental delay and 28.7% had repeated a grade at school. O f those with both seizures and behavioural problems, 57.1% required special education. Studies on African populations have found similar patterns of results. Eighteen percent o f Nigerian children with epilepsy were diagnosed as having learning difficulties (Iloeje and Paed, 1989), a rate that was increased in children with early-onset seizures or status epilepticus. Seventy-one percent of a group of rural South African children with epilepsy were found to have developmental disabilities, nearly one quarter o f which were moderate to severe (Christianson, et al., 2000).

Epidemiological research has also suggested that difficulties in childhood may have implications for adult life. In a long-term follow-up of adults with early-onset epilepsies, participants with uncomplicated epilepsy had significantly poorer outcomes on social, educational and employment-related variables than matched

controls o f similar socioeconomic status (Sillanpaa, et al., 1998). These results

remained consistent even in participants who were in remission without medication, in some cases for more than 20 years.

3.3.1 Interrelationships between epilepsy, cognition and behaviour

Epilepsy may interact with cognition in a number o f different ways:

1. Brain damage or dysfunction causes both epilepsy and cognitive impairments. 2. Epilepsy causes brain damage or dysfunction, which results in cognitive

impairments.

3. Epilepsy directly causes cognitive impairments.

The interrelationship between epilepsy and behaviour is more complex and reflects the interaction of biological and psychosocial factors. Besag (2002) recommends a five-fold systematic approach to determining causality in epilepsy-related behavioural disorders. First, the epilepsy itself can cause behavioural changes related to the peri- ictal or post-ictal period, inter-ictal psychoses, focal frontal or temporal lobe discharges or frequent absence seizures. The effects of antiepileptic medication on behaviour and cognition are well-recognised (Aldenkamp, 2001; Kalviainen, et al., 1996; Kwan and Brodie, 2001), as are negative reactions from others, both in the form of teasing and over-protectiveness. As with cognitive impairments, brain damage or dysfunction may affect behaviour, either directly, for example disinhibition as a result o f frontal lobe dysfunction or indirectly, with frustration at the loss o f other cognitive functions such as memory or language. Finally, behavioural disturbances may result from causes that are completely independent o f the epilepsy, as in any other child.

Children with epilepsy form a clinically heterogeneous group, differing along dimensions such as aetiology, seizure variables, electroencephalographic (EEG) activity, antiepileptic medication, age, sex and environment (Cull, 1988; Goldstein, 1991; Niemann, et al., 1985; Strauss, et al., 1995). In terms of aetiology, children

with symptomatic epilepsy are more likely to have cognitive or behavioural impairments than those with idiopathic epilepsy (Cull, 1988). Seizure syndrome is a significant influence on the risk of impairment, with malignant syndromes of epilepsy often resulting in very high rates of impairment. For example. West’s syndrome and Lennox-Gastaut syndrome may result in severe developmental impairments in 80- 90% of children (Neville, 1997). The study o f cognitive and behavioural comorbidity is further complicated by the multiplicity of other variables that may influence development in children with epilepsy and the fact that such children can be difficult to study reliably, showing fluctuating performance from one testing period to another (Metz-Lutz and Massa, 1999).

3.3.2 State dependent 'versus permanent disorders

Cognitive disorders associated with epilepsy fall into two categories: ‘permanent’ or ‘state dependent’. State-dependent learning disorders describe potentially reversible or treatable cognitive impairments, as opposed to the permanent learning disorder resulting from brain damage or stable brain dysfunction (Comaggia and Gobbi, 2001). Prolonged status epilepticus is the most well-known situation in which epilepsy may cause cognitive impairments through damage to the brain (Scott, et al., 1998). Nonconvulsive status epilepticus, classically accompanied by continuous generalised spike-wave discharges, is an example of ictal state-dependent cognitive impairment (Besag, 2002).

There is an emerging literature suggesting that there are children in whom epileptiform discharges may cause transitory cognitive impairments (TCIs) in the absence of clinical seizures (Aarts, et al., 1984; Binnie, 1993; Binnie, 2001), affecting alertness and memory (Aldenkamp, et al., 2001) and psychosocial functions (Marston, et al., 1993). For example, focal or generalised epileptiform discharges of less than one second duration to more than three seconds have been found to momentarily impair performance on intelligence tests (Kasteleijn-Nolst Trenite, et al., 1988; Siebelink, et al., 1988). Left-sided or dominant-hemisphere discharges have been shown to impair verbal tasks such as reading (Kasteleijn-Nolst Trenite, et al., 1990) whereas right-sided discharges affect visuo-spatial functioning (Aarts, et al., 1984).

Post-ictal state-dependent cognitive impairments may be persisting rather than transitory if the seizures experienced are so frequent as to induce an almost constant post-ictal state. It has been suggested that, if allowed to continue for a long time, state-dependent learning disorders may produce permanent learning disorders (Comaggia and Gobbi, 2001). Evidence to support this from rare models of epilepsy, such as Landau-Kleffher syndrome (LKS), benign epilepsy with centrotemporal or Rolandic spikes (BECRS) and the syndrome of continuous spikes and waves during slow sleep (CSWS), will be discussed in the following section.