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Adult onset IGE is more common than generally realised
The commonest epileptic syndrome is the so-called idiopathic generalised epilepsy (IGE), which accounts for at least a third of all cases of epilepsy in the community.1 This proportion is even higher in the paediatric age range. The syndrome is characterised by the presence of generalised tonic clonic, myoclonic, and typical absence seizures on their own or in different combinations. The onset is usually before the age of 16. IGE has a typical electroencephalographic (EEG) pattern with paroxysms of generalised spike and wave and polyspike discharges, which is the hallmark of the syndrome. Age of onset and main seizure type are used to classify IGE further into four main subsyndromes: IGE with tonic-clonic seizures only, childhood absence epilepsy, juvenile absence epilepsy, and juvenile myoclonic epilepsy. As the majority of patients have the onset of IGE in childhood or adolescence, the international classification currently in use only recognises subsyndromes with onset in childhood. Although it is well known in epilepsy specialist centres that IGE may present in adult life, this is often not well recognised by neurologists who do not have a specialist interest in epilepsy. Therefore, the paper by Marini et al (this issue, page 192-196)2 is of interest as they describe 34 consecutive patients with IGE beginning after the second decade of life, including several people over the age of 50 presenting with “de novo” IGE. The authors quite rightly suggest that adult onset IGE is more common than generally realised and this is an important takeaway message. The second message is the importance of a directed diagnostic EEG strategy in all patients presenting with a first unprovoked epileptic seizure independent of age. This goes against the suggestion that after the age of 25 years, EEG is less important as an investigative tool in epilepsy.3 The authors’ practice is to record an early postictal EEG, followed by a sleep deprivation EEG in negative cases and they have previously shown that this leads to a higher diagnostic yield in first seizure cases in all ages.4 A second spin off seems to be a relatively frequent identification of adult-onset IGE that might otherwise have been regarded as being partial epilepsy of uncertain origin. The paper also highlights the growing importance of genetics in epilepsy, particularly in IGE.5 Early onset IGE has a genetic aetiology with complex inheritance. Family and twin studies suggest a common genetic origin for all subtypes of IGE and this seems also to apply to the late onset form. Currently, intensive work is ongoing to clarify fully the genetic blueprints of IGE, and the Melbourne group, which authored this article, are major players in this area. For the general neurologist the recognition of adult-onset IGE has implications for accurate diagnosis and treatment. Adults with a family history of IGE and in whom other causes have been ruled out are prime candidates for adult-onset IGE. The diagnosis of adult-onset IGE can avoid unnecessary investigations, direct appropriate treatment, and allow an optimistic prognosis, and this should not be forgotten.
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