Cognitive impairments are very common in patients with epilepsy. If cognitive impairments are due to neuropathology (which causes the epilepsy) or due the clinical manifestations (for example a seizure) is the subject of this article.

Do seizures cause brain damage?

Experimental research conducted on animals showed that seizures on an immature brain produce less prominent damage to the brain compared to a mature brain. But when an immature brain is damaged by a seizure; neuronal loss, neoneurogenesis and synaptic reorganization, increased susceptibility to evoked and spontaneous seizures are found, which makes the brain more vulnerable to a new seizure. The cumulative effect of seizures cause even worse behavioural and cognitive deficits.

The study on humans does not have this clear conclusion and different proposals have been made. But recently is found that epilepsy in a developing brain causes a reduction in white brain matter and this was significantly associated with cognitive deficits, compared to a control group.

Methodological issues

Because measures on localization-related symptomatic epilepsy only measure a state, and not a change, it is hard to distinguish between the effects of epilepsy as a symptom and the effects of a seizure. A patient with idiopathic epilepsy does not have an identifiable cerebral disease, so it’s possible to measure the effects of a seizure. The only problem is that patients with idiopathic epilepsy usually only suffer from mild cognitive deficits. Longitudinal studies is another option, but the problem with this is the cumulative effect of seizures. This also increases the risk of seizure related closed-head injuries. Besides that the dose of antiepileptic drugs will be higher, causing cognitive impairments. Because of this not all patients will be in the same ‘stage’ at the same moment, which makes them hard to compare. The last problem with measuring epilepsy is the absence of a test-her test learning effect in patients with epilepsy, mostly explained from cognitive deficits. But to establish this there must be a control group making both tests too.

Cognitive consequences of seizures in children

Bourgeois et al. found that children with a high frequency of seizures and a toxic drug level showed an IQ drop from 10 points. Ellenberg et al. showed that children with relatively few seizures showed no IQ drop. Neyens et al. found that children with epilepsy have an already lower IQ score (compared to controls) and their grow in IQ score is smaller. This effect is mostly seen in children with a recent onset of a seizure, not in the children with the most seizures. Bjornaes et al. showed that even after surgery and the drug treatment period children with active seizures show IQ drops, but when the children became epilepsy free after the surgery the IQ-decline stopped.

Studies showed that epilepsy does not have this big effects on cognition. The percent of patients in the study with severe cognitive deficits also had poor parenting, unhappy family situations and prior behaviour problems, which can also cause the deficits. Nolan et al. found that the age of onset, high seizure frequency and higher number/intake of antiepileptic drugs were a precursor of IQ decline. Caplan et al. found a fourth important factor: EEG. Also the type of syndrome is a precursor, with performances from best to worse in this order: 1. generalized idiopathic epilepsy group/central epilepsy group/temporal lobe epilepsy group 2. non-localized partial epilepsy/frontal lobe epilepsy 3.generalized symptomatic epilepsy.

Cognitive consequences of adults in children

Dodril and Wilensky found that adults with a history of status epilepticus in a 5 year period have a significantly smaller increase in IQ compared to adults who have not this history. Selwa et al. investigated people with a temporal lobe epilepsy, who showed no impairments on IQ and memory over 8 years. However, Helmstaedler found that these patients had impairments in verbal and figural memory. Holmes et al. also showed the there was no change in IQ on high frequency seizure patients, but he did find that visual memory, attention, perception and problem solving were significantly impaired. Studies correlating the neuropsychological morbidity with the duration of epilepsy also give mixed results.

Conclusion

Intellectual performance does measurably decline in children and adults. But due to many other factors, the effect of the seizure alone is hard to distinguish, but seems limited.