Aetiology

Epilepsy is better defined as a symptom, rather than a disease which arises due to various conditions that involves the brain (1).

According to a UK National General Practice Study of Epilepsy, 60% of people with newly diagnosed or suspected epileptic seizures had epilepsy with no identifiable aetiology while in 15% and 6% vascular disease and tumour was the aetiology respectively (2).

When considering causes of seizures then they may be considered in terms of:

• idiopathic (60% of cases)
• the result of structural derangement of the brain
• the result of infection
• the result of metabolic derangement
• the result of the action of or withdrawal from drugs

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 (3).

• 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. At the present time, there is virtually no knowledge to support specific environmental influences as causes of or contributors to these forms of epilepsy
    
    
• 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. They may also be of genetic origin (e.g., tuberous sclerosis, many malformations of cortical development); however, as we currently understand it, 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) Maguire M et al. Clinical Evidence Handbook. A Publication of BMJ Publishing Group. Epilepsy (Generalized and Partial).Am Fam Physician. 2011;83(4):461-463
• (2) National Clinical Guideline Centre (NCGC) 2012. The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care.
• (3) 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.