Aetiology

Advances in understanding epilepsy in childhood have come from the newer medical technologies. Recognition of a typical spike-wave pattern has led to the identification of benign focal epilepsy; CT scanning and high-resolution magnetic resonance imaging ( MRI) have led to the recognition of mesial temporal sclerosis, tuberous sclerosis, neuroblast migrational disorders, and small temporal lobe tumours. Positron emission tomography scanning can demonstrate lesions undetected by MRI, such as focal lesions in patients with hypsarrthymia. Advances in surgical procedures have decreased the risks associated with callosotomies and hemispherectomies used for catastrophic seizures. New understanding about neurotransmitters involved in the production and inhibition of seizures has led to advances in seizure medications.

Epileptic seizures are the result of an imbalance between inhibitory (g-aminobutyric acid ( GABA)) and excitatory (glutamate) neurotransmitter systems. Neuronal hyperexcitability leading to seizures may result from decreased inhibition or increased excitation. (58) Epilepsy has its highest incidence in childhood, suggesting that the immature brain is more vulnerable to seizures than the mature brain—a finding that is borne out by animal studies. Decreased inhibition or increased excitation may result in neuronal excitability and seizures.(58) The specific mechanisms responsible for this imbalance remain uncertain.(58) However, it is known that the binding of GABA to GABAa receptors opens a chloride channel (ionophore) leading to a flux of chloride ions and consequent membrane hyperpolarization: it is also known that there are fewer GABAA high-affinity receptors in immature animals. Similarly, there are maturational differences in the development of major ionotrophic receptors in excitatory systems and in the activation of M-methyl-D-aspartate receptors. In younger animals this results in larger excitatory post-synaptic potentials. It remains a puzzle why certain seizure types are age-specific in their onset.(59)

Epilepsy syndromes may have a genetic basis.(6,9 Gene localization for five epilepsy syndromes with Mendelian inheritance are recognized, and localization has been suggested in three epilepsies with complex inheritance. Those epilepsies with a single gene inheritance include symptomatic epilepsies with associated diffuse brain dysfunction and idiopathic epilepsies, where the seizures are the primary brain abnormality. Idiopathic single gene epilepsies include benign, familial neonatal convulsions, in which genetic linkage to chromosomes 20q and 8q have been demonstrated. to date, four autosomal dominant forms of epilepsy have been described. The first genetic defect described in idiopathic epilepsy is in autosomal-dominant nocturnal frontal-lobe epilepsy ( ADNFLE), where a genetic defect with two different mutations in the a4-subunit of the nicotinic acetylcholine receptor has been identified. Subsequently, it has been shown that, although the ADNFLE phenotype is clinically homogeneous, there are a variety of molecular deficits responsible for this disorder, (61) highlighting the complexity in understanding the basic mechanisms of epileptogenesis. Molecular genetic studies are expected to lead to the discovery of other epilepsy genes. Investigation of animal models of epilepsy are continuing. (62>

The aetiology of temporal lobe seizures includes mesial temporal sclerosis, tumours, and cortical dysplasia. The younger the child, the less frequent is mesial temporal sclerosis. Other factors linked to aetiology are proposed: temporal lobe hypoperfusion and hypometabolism in Landau-Kleffner syndrome, and diffuse cortical and subcortical hypoperfusion in Lennox-Gastaut syndrome.

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