Task Force Proposes Revised, More Practical Definition of Epilepsy

A task force commissioned by the International League Against Epilepsy (ILAE) to “formulate an operational definition of epilepsy for purposes of clinical diagnosis” has published new recommendations that offer a more detailed view of the condition that is more in line with how clinicians actually think about the seizure condition and is designed to aid in making treatment decisions.

The authors of the ILAE Official Report “A Practical Clinical Definition of Epilepsy,” published in Epilepsia, noted that a previous task force report (published in 2005) defined an epileptic seizure as “a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain,” and defined epilepsy as “a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures, and by the neurobiologic, cognitive, psychological, and social consequences of this condition. The definition of epilepsy requires the occurrence of at least one epileptic seizure.”

These definitions were problematic on several levels. In a news release accompanying publication of the task force’s report, lead author Dr. Robert Fisher, Department of Neurology and Neurological Sciences, Stanford University School of Medicine, said the current definition of epilepsy “does not allow a patient to outgrow epilepsy, nor does it take into account some clinicians' views that epilepsy is present after a first unprovoked seizure when there is a high risk for another.”

He said the revised definition and approach outlined by the new task force “resolves these issues with the new, more practical, definition of epilepsy that is aimed at clinicians.”

The new, practical clinical definition states epilepsy is a disease of the brain defined by any of the following conditions:

• At least two unprovoked (or reflex) seizures occurring more than 24 hours apart
• One unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk (at least 60%) after two unprovoked seizures, occurring over the next 10 years
• Diagnosis of an epilepsy syndrome

The authors also wrote that “Epilepsy is considered to be resolved for individuals who had an age-dependent epilepsy syndrome but are now past the applicable age or those who have remained seizure-free for the last 10 years, with no seizure medicines for the last 5 years.”

The revised definition of epilepsy has several potential implications for treatment. The authors wrote that although “diagnosing epilepsy after a single unprovoked seizure when there is high risk for recurrence may or may not lead to a decision to initiate treatment,” the new definition “may provide support to a physician who wishes to treat a patient with high recurrence risk after a single unprovoked seizure.”

However, the authors cautioned that “a treatment decision is distinct from a diagnosis, and should be individualized depending upon the desires of the patient, the individual risk-benefit ratio and the available options. The physician should weigh the possible avoidance of a second seizure with associated risks against the risk for drug-related side effects and costs for the patients.”

Other potential consequences of adopting the new, more practical definition of epilepsy could include:

• Improved outcomes due to clinicians giving greater consideration to the risk of recurrence after a single unprovoked seizure
• Clinicians becoming more comfortable in initiating individualized treatment after initial unprovoked seizures
• Earlier diagnoses preventing unnecessary risks of physical injuries or social consequences resulting from recurrent seizures in patients deemed to be susceptible to a high risk for recurrence
• Expanded opportunity for disease-modifying interventions that prevent the progression of epilepsy and onset of comorbidities

In their concluding remarks, the authors acknowledged that “the new definition is more complicated than is the old definition” of epilepsy and that it “is intended for clinical diagnosis, and might not be suitable for all research studies.” By implying that “epilepsy also can be considered to be present after one unprovoked seizure in individuals who have other factors that are associated with a high likelihood of a persistently lowered seizure threshold and therefore a high recurrence risk,” the new definition of epilepsy “brings the term in concordance with common use by most epileptologists.”