Classification of the epilepsies and epilepsy syndromes

Classification of epilepsy is important for the management and prognosis and failure to do so will result in inappropriate treatment and persistence of seizures (1).

The 1989 ILAE classification of epilepsies and epileptic syndromes is as follows:

• localization-related (local, focal, partial) epilepsies and syndromes
  • idiopathic
  • symptomatic
  • cryptogenic
• generalized epilepsies and syndromes
  • idiopathic (with age-related onset) - juvenile myoclonic epilepsy, benign neonatal familial convulsions etc.
  • cryptogenic or symptomatic - West syndrome (infantile spasms), Lennox-Gastaut syndrome
  • symptomatic
• epilepsies and syndromes undetermined whether local or generalized
  • with both generalized and focal seizures - neonatal seizures, severe myoclonic epilepsy in infancy etc
  • without unequivocal generalized or focal features
• special syndromes
  • situation-related seizures - febrile convulsions, isolated seizures or isolated status epilepticus etc (1)

Although this classification remains in common use it has been the subject of criticism and debate. Therefore

• in 2001, the ILAE proposed that clinicians and researchers should use a multi-axial diagnostic scheme which includes:
  • description of seizure (ictal phenomenology)
  • seizure type
  • syndrome
  • aetiology
  • impairment (optional parameter) (1).
• a further report of the task force for classification was published in 2006 with an updated list of epilepsy syndromes
• in the latest proposed terminology (2010) the descriptors of aetiology have been updated, the terms idiopathic, symptomatic and cryptogenic have been replaced with genetic, structural/metabolic and unknown (1).

The ILAE has recommended the following three terms and their associated concepts for underlying type or cause (aetiology) of epilepsy instead of the terms idiopathic, symptomatic and cryptogenic (2).

• Genetic:
  • concept of genetic epilepsy is that the epilepsy is, as best as understood, the direct result of a known or presumed genetic defect(s) in which seizures 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 evidence for a central role of a genetic component may come from appropriately designed family studies
  • designation of the fundamental nature of the disorder as genetic does not exclude the possibility that environmental factors (outside the individual) may contribute to the expression of disease
    
    
• Structural/metabolic:
  • conceptually, there is a distinct other structural or metabolic condition or disease that has been demonstrated to be associated with a substantially increased risk of developing epilepsy in appropriately designed studies. Structural lesions of course include acquired disorders such as stroke, trauma, and infection
  • may also be of genetic origin (e.g., tuberous sclerosis, many malformations of cortical development); however there is a separate disorder interposed between the genetic defect and the epilepsy
    
    
• Unknown cause:
  • unknown is meant to be viewed neutrally and 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 as yet unrecognized disorder

.Reference:

• (1) National Clinical Guideline Centre (NCGC) 2012. The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care.
• (2) Berg AT et al. Revised terminology and concepts for organization of seizures and epilepsies: report of the ILAE Commission on Classification and Terminology, 2005-2009. Epilepsia. 2010;51(4):676-85.