Page 9 - ILAE_Lectures_2015

Chapter 2

Classification and terminology to organise seizures and epilepsies

MARK P. RICHARDSON1 , DAVID W. CHADWICK2 and TIM WEHNER3

1Institute of Epileptology, King’s College London, 2Walton Centre for Neurology and
Neurosurgery, Fazakerley, Liverpool, and 3National Hospital for Neurology and
Neurosurgery, London
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Classification schemes can appear dull and cumbersome, but are crucial to facilitate diagnosis
of epilepsy, communication between health professionals, and communication between
professionals and people with epilepsy.

Because there is not a one-to-one mapping between underlying disease and clinical
phenomenology in the epilepsies, there is a need for at least two separate schemes: a
classification of seizures (i.e. a scheme based on clinically observable phenomenology) and
an organisation* of epilepsies (i.e. a scheme that considers aspects beyond seizure semiology
such as age at onset, neuroimaging and genetic aspects, aetiology, and prognosis). Even more
ambitiously, the International League against Epilepsy (ILAE) has recently proposed a set of
classification schemes based on five axes: ictal phenomenology, seizure type, syndrome,
aetiology, and impairment. However, this approach has not yet achieved consensus approval.

The ILAE commission on classification and terminology has created an online manual at
https://www.epilepsydiagnosis.org/index.html. This practical tool provides a three-tiered
structure of seizure classification, epilepsy syndromes, and aetiologic categories.

The ILAE established a standardised classification and terminology for epileptic seizures in
1981. It is important to recognise that this scheme utilised seizure manifestations and EEG
findings only. In the 30 plus years since then, advances, especially in neuroimaging and
genetics, have had a major impact on our understanding of epilepsy. The ILAE has recognised
the pressing need for a new scheme, and the proposal from 2010 will be discussed here
alongside the 1981 scheme (Tables 1 and 2).

Both classification schemes are based on the widely accepted concept that seizures can be
focal or generalised. A generalised seizure is conceptualised as originating within, and
rapidly engaging neuronal networks in both hemispheres (though not necessarily the entire
cortex). Nonetheless, generalised seizures can be asymmetric to some extent in their clinical
and EEG manifestations. A focal seizure is thought to arise within an area confined to one
hemisphere. Focal seizures can spread within the same hemisphere, and/or to areas in the
contralateral hemisphere, and evolve into a generalised convulsive seizure (i.e. adopt the
semiology of a primary generalised tonic-clonic seizure). The (initial) seizure semiology in
focal seizures often reflects the functional role of the cortex that is involved at the onset and
early evolution of the seizure.

*The ILAE commission uses the term organisation to recognise that knowledge about underlying seizure
mechanisms is evolving and often still inadequate to allow a scientifically based classification.