Page 120 - ILAE_Lectures_2015

Chapter 11

Idiopathic generalised epilepsies

MICHAEL KOUTROUMANIDIS

St Thomas’ Hospital, Guy’s and St Thomas’ NHS Foundation Trust, London
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Introduction

The idiopathic generalised epilepsies (IGE) constitute roughly one-third of all epilepsies.
Etymologically, the term ‘idiopathic’ comes from the Greek word ‘idios’, which simply
means ‘oneself’. An idiopathic syndrome therefore may be conceptualised as a disease unto
itself, a sui generis condition. It follows that an idiopathic epilepsy syndrome:

 Consists only of recurrent epileptic seizures
 Is not associated with structural brain lesions on MRI or abnormal neurological

symptoms and/or signs inter-ictally and implies normal neuropsychological
status.

It should be also made clear that the term idiopathic is not synonymous with ‘benign’, as
some subtypes such as juvenile myoclonic epilepsy (JME) are often life-long conditions, or
with ‘genetic’, as not all genetic conditions are idiopathic, such as the progressive myoclonic
epilepsies, or finally with ‘unknown aetiology’, as the genetic background of some subtypes
such as JME and childhood absence epilepsy (CAE) has already been identified1.

The term ‘generalised’ refers to the seizures ‘in which the first clinical changes indicate initial
involvement of both hemispheres… The ictal encephalographic patterns initially are
bilateral’2,3. This statement however is not entirely true. Video-EEG experience has taught us
that typical absences (TA) may show an interhemispheric difference of 100–200 ms at their
onset (without consistent side emphasis), and that some patients may show focal or
lateralising ictal clinical features4,5. Finally, at least 40% of patients with idiopathic
generalised epilepsies (IGE) display non-localising focal discharges in the inter-ictal EEG
(with or without generalised discharges)4-6.

The IGEs comprise several sub-syndromes, characterised by all or some of the three seizure
types – TA, myoclonic jerks and generalised tonic-clonic seizures (GTCS) – in different
combinations and emphasis. These sub-syndromes usually have distinct electroclinical
features and prognosis; some are life-long while others are age-related. However, accurate
syndromic diagnosis may not be possible from the first presentation, and a number of patients
with IGE may be difficult to classify.

The classification of IGE sub-syndromes over recent years has been controversial and a lively
debate continues in view of the long-awaited new classification scheme of the ILAE7. There
are two schools of thought: the ‘lumpers’, who hold that although IGE sub-syndromes can be
recognised, their boundaries are indistinct, and that all forms of IGE fall into the same
neurobiological continuum with genetic relationships8,9; and the ‘splitters’, who take the view
that precise syndromic classification provides a nosologic framework of utmost importance
for treatment and prognosis of an individual patient, and a sound basis for genetic and
neurobiological research10-12.