Summary of key recommendations from the Commission on Classification and Terminology –
For Discussion at the ICE in Budapest
The Commission on Classification and Terminology will be holding a parallel session at the ICE in Budapest on 30 June 2009 from 10:30am – 12:00pm in Hall #3. We present the following synopsis of some of the key recommendations regarding terminology and concepts used in the classifications of the epilepsies and epileptic seizures which will be discussed during this session. A full report of the recommendations from the Commission on Classification and Terminology is underway. A draft is available by following the link at the end of this summary document
1. Mode of seizure onset and Classification of Seizures:
Generalized epileptic seizures originate at some point within, and rapidly engage, bilaterally distributed networks. Such bilateral networks can include cortical and subcortical structures, but do not necessarily include the entire cortex. Although individual seizure onsets can appear localized, the location and lateralization are not consistent from one seizure to another. Generalized seizures can be asymmetric.
Focal epileptic seizures originate within networks limited to one hemisphere, which may be discretely localized or more widely distributed. For each seizure type, ictal onset is consistent from one seizure to another with preferential propagation patterns, which can involve the contralateral hemisphere. In some cases, however, there is more than one epileptogenic network, and more than one seizure type, but each individual seizure type has a consistent site of onset.
Specific changes recommended to the 1981 classification of seizures are as follows:
- Neonatal seizures will no longer regarded as a separate entity.
- The previous subclassification of absence seizures has been simplified and altered. Myoclonic absence seizures and eyelid myoclonia are now recognized.
- Epileptic spasms are now included and are classified under generalized seizures. Note, however, that spasms may be associated with focal pathology and seizure initiation, thus spasms could potentially exist in either category.
- Under focal seizures the distinction between the different types (e.g. complex partial and simple partial) is eliminated. It is important however to recognize that impairment of awareness or other dyscognitive features, localization, and progression of ictal events can be of primary importance in the evaluation of individual patients and for specific purposes (e.g. randomized trials, surgery). Nothing in this recommendation precludes describing focal seizures according to these features.
- Myoclonic atonic (sometimes referred to as myoclonic astatic) seizures are now recognized
- The category of unclassified epileptic seizures has been eliminated
Recommended classification of seizures
GENERALIZED SEIZURES
Tonic clonic (in any combination)
Absence
1.Typical
2. Atypical
3. Absence with special features
Myoclonic absence
Eyelid myoclonia
Myoclonic
1. Myoclonic
2. Myoclonic atonic
3. Myoclonic tonic
Clonic
Tonic
Atonic
Epileptic spasms
FOCAL SEIZURES
These can be further described as a function of seizure severity, putative site of origin, elemental sequence of events, or other features.
Syndromes themselves will no longer be classified as being focal (or localization-related or partial) versus generalized.
2. Syndrome versus epilepsy:
We recommend that the use of the term “syndrome” be restricted to a group of clinical entities that are reliably identified by a cluster of electro-clinical characteristics. Patients whose epilepsy does not fit the criteria for a specific electro-clinical syndrome can be described with respect to a variety of clinically relevant factors. We recommend that those with known structural-metabolic causes be first organized by those causes (e.g. stroke, malformation of cortical development). Those with epilepsy of unknown cause may be grouped and organized according to whichever dimensions are most useful for a given purposes (seizure type, age at onset, interictal focus etc) This does not, however, provide a precise (syndromic) diagnosis of their epilepsy.
In the 1989 publication, syndromes were organized primarily according to “mode” of expression (localization-related versus generalized) and underlying cause (idiopathic, symptomatic, and cryptogenic). We recommend that such a rigid approach to classification be abandoned and, in preparation for the paradigmatic shift in classification, which will be forthcoming, that we organize our knowledge regarding syndromes and epilepsies in a flexible, multidimensional manner as appropriate for the specific purpose.
3. Underlying type of cause (etiology)
We propose that the current terms, idiopathic, symptomatic, and cryptogenic used to classify epilepsies be replaced with the terms genetic, structural/metabolic, and unknown.
1. Instead of idiopathic, the term
genetic (or presumed genetic) epilepsy is recommended. The concept of genetic epilepsy is that
the seizures are, as best as is understood, the direct result of a known or presumed genetic defect(s) in which seiz
ures are the core symptom of the disorder. The knowledge regarding the genetic contributions may derive from specific molecular genetic studies that have been well replicated and even become the basis of diagnostic tests (e.g.
SCN1A and Dravet syndrome) or the central role of a genetic component may be
presumed based on analyses of appropriately designed family studies. Note that in the 1989 classification, Dravet syndrome was not classified as idiopathic epilepsy. It will now be considered as a genetic epilepsy. In doing this, we will no longer equate cause with prognosis; the implication that ‘idiopathic’ implies ‘benign’ is intentionally discarded.
2. Instead of “symptomatic” the term “
structural/metabolic” is recommended. A structural/metabolic cause of epilepsy represents a distinct other condition or disease that has been demonstrated to be associated with a substantially increased risk of developing epilepsy. Structural lesions include acquired disorders such stroke, trauma, and infection. As well as those of genetic origin (e.g. tuberous sclerosis, many malformations of cortical development, in-born errors of metabolism). The distinction is that there is a separate disorder that appears to be interposed between the genetic defect and the epilepsy.
A clear determination for genetic disorders may not always be readily made. We recommend that the role of the specific genetic error be recognized but that it is not necessary to pigeon-hole the cause of the disorder further unless there is an adequate basis for doing so. The overly simplistic designation of “genetic” versus “structural-metabolic” will ultimately be replaced by a more precise characterization of the underlying cause. Groups and names for groups of causes should ultimately reflect natural classes.
3. To replace the term “cryptogenic,” the term
“epilepsy of unknown cause” is recommended. Unlike “cryptogenic” which has at times been linked to the presumption of “symptomatic,” in the sense of structural/metabolic cause, unknown is meant to be taken neutrally to designate that the nature of the underlying cause is as yet unknown, it may have a fundamental genetic defect at its core or it may be the consequence of a separate disorder or condition not yet recognized. Examples of syndromes that would be classified as “of unknown cause” include migrating partial seizures of infancy and myoclonic epilepsy in infancy (formerly benign myoclonic epilepsy of infancy. At the present time, it might be reasonable to include some of the traditional “idiopathic” developmental syndromes such as benign rolandic epilepsy and the benign occipital epilepsies of childhood, both Panayiotopoulos and Gastaut types.in this category as well.
Certain electro-clinical syndromes, such as infantile spasms, may have multiple different causes. This should be acknowledged when describing the syndrome in general, and the specific cause should be identified for the individual patient.
For those interested in further detail and discussion, a draft of the working document is available:
LINK
