The International League Against Epilepsy has revised its definition of epilepsy to include additional criteria for clinical diagnosis, according to a report from the organization published April 14.
The existing definition of the disease requires that a patient have two unprovoked seizures more than 24 hours apart, wrote Dr. Robert S. Fisher of the department of neurology and neurological sciences at Stanford (Calif.) University. The new proposed definition expands upon this to include two additional criteria: 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; and diagnosis of an epilepsy syndrome (Epilepsia 2014;55:475-82).
The changes to the definition are the result of attempts by an International League Against Epilepsy (ILAE) task force to account for clinical situations that may not be covered by the "two unprovoked seizures" requirement under the ILAE’s existing definition of epilepsy, originally published in 2005 (Epilepsia 2005;46:470-2).
Dr. Fisher and his colleagues differentiated between provoked and unprovoked seizures in the report, but emphasized that risk of seizure recurrence should also be considered when diagnosing epilepsy, rather than provocative factors alone.
"Epilepsy exists in a patient who has had a seizure and whose brain ... demonstrates a pathologic and enduring tendency to have recurrent seizures," they said. "This tendency can be imagined as a pathologic lowering of the seizure threshold, when compared to persons without the condition."
Under the previous definition, recurrent reflex seizures, such as those caused by sensitivity to light, would not be considered epilepsy because they are provoked. But the new "operational" definition would classify such a patient with epilepsy. In such a situation, "even though the seizures are provoked, the tendency to respond repeatedly to such stimuli with seizures meets the conceptual definition of epilepsy, in that reflex epilepsies are associated with an enduring abnormal predisposition to have such seizures," the authors said.
In contrast, a seizure following a "transient factor" such as a concussion in an otherwise normal brain would not meet the epilepsy criteria. A brain tumor or stroke, however, may meet the criteria for an epilepsy diagnosis depending on recurrence risk.
"Etiology should not be confused with provocative factors, as some etiologies will produce an enduring tendency to have seizures," the authors noted.
The task force acknowledged in the report that recurrence risks are unknown in most cases, but that in the absence of this knowledge, an epilepsy diagnosis may be made when the second unprovoked seizure occurs.
"On the other hand, if information is available to indicate that risk for a second seizure exceeds that which is usually considered to be epilepsy (about 60%), then epilepsy can be considered to be present," they added.
In addition to broadening the criteria for an epilepsy diagnosis, the new operational definition also clarifies that if a patient presents with evidence of an epilepsy syndrome, then epilepsy can indeed be considered present, regardless of the risk of subsequent seizures.
The new definition also allows for an individual’s epilepsy to be considered "resolved" if the person either had an age-dependent epilepsy syndrome but is now past the applicable age or has remained free of seizures for 10 years without the use of seizure medications for the last 5 years.
Dr. Fisher and his colleagues said the new ILAE definition of epilepsy seeks to bring "greater clarity and clinical relevance to the diagnostic process," but acknowledged that specialized skills in assessing recurrence risk and interpreting potential epileptogenicity of MRI results is vital to the process and may not always be available in primary care settings.
"When in doubt, practitioners should consider referring a patient to a specialized epilepsy center with experience in diagnosis," the task force said.
Although the new definition may improve clinical outcomes by encouraging doctors to consider recurrence risk after a single seizure, studies about seizure recurrence risk are limited and most diagnoses will still need to be made using the "two unprovoked seizures" rule, the authors said.
However, as more information about recurrence risks becomes available over time, "application of the epilepsy definitions will become more precise and more useful," they added.
In an online survey, the task force is seeking public comments on the proposed new definition, particularly in instances such as recurrence risk or when seizures might be considered "resolved" where an expert consensus was reached in lieu of lack of data.
Dr. Fisher and his associates reported receiving support and/or serving as consultants for numerous companies involved in epilepsy therapeutics.