In 2017, the International League Against Epilepsy (ILAE) released updated classifications for epilepsy. The new classifications better reflect current scientific understanding of seizures, as the prior classifications had last been updated in 1989.
Before this new update, seizures were divided into two broad categories — partial-onset seizures and generalized seizures. Partial-onset seizures originate in one side, or hemisphere, of the brain and generalized seizures start in both sides of the brain.
The new classification considers three main factors when defining seizures:
For example, simple partial seizures have been renamed focal onset aware seizures, and complex partial seizures have been reclassified as focal onset impaired awareness seizures.
Why the changes? In an interview in Epigraph, Ingrid Scheffer, who led the ILAE effort to reclassify seizures, said the group was focused on creating “transparent language” for seizure types. “We wanted language that patients could understand, not just doctors,” she said.
Seizure type is now identified by point of origin, awareness level, and accompanying behaviors.
The point of origin for each type of seizure is now classified into one of four categories:
Awareness levels during seizures have four distinguishing features:
Behaviors that accompany focal onset seizures also have classifications:
These behaviors accompany generalized onset seizures:
Read more about types of focal seizures and their symptoms.
Read about treatments for focal seizures.
Understanding the history of epilepsy research can shed light on how and why terminology has changed, and why the current set of terms is the most accurate so far. The ancient Greeks coined the term epilepsy (meaning “to seize”) and attributed the condition to an attack by a demon or a god. Babylonians documented seizures on clay tablets. Ancient Persians believed the source was mental illness, while Chinese physicians more than 2,500 years ago believed epilepsy was caused by an excess of secretions in the brain.
By the 1860s, British neurologist John Hughlings Jackson had determined that seizures were due to activity in the brain. For the first time, he hypothesized that seizures present differently depending upon the part of the brain from which they originated. In the 1930s, this groundbreaking theory inspired Canadian-American neurosurgeon Wilder Graves Penfield to use electrostimulation in surgery to locate the brain tissue responsible for behavior during a seizure. Once identified, he pioneered the concept of removing this affected tissue. Henri Jean Pascal Gastaut took that research one step further, working with his wife, Yvette, to define five major human electroencephalogram (EEG) patterns. He also discovered Gastaut syndrome (photosensitive epilepsy) and Lennox-Gastaut syndrome (severe childhood encephalopathy).
Significant advances in diagnostic imaging have been made in the last 50 years. New imaging tools include computerized tomography (CT) scans, magnetic resonance imaging (MRI), single photon emission computerized tomography (SPECT) and positron-emission tomography (PET), magnetic resonance spectroscopy, and magnetoencephalography (MEG). With each new tool, scientists have become better able to understand brain activity. These tools have also dramatically changed the possibilities of surgery as a treatment for epilepsy. In more recent times, advances in imaging have led to the possibility of neuromodulation — using devices that electrically stimulate the nervous system — to treat epilepsy in a less invasive way.
As scientists gained a deeper understanding of the brain and epilepsy, formal organizations were established to study epilepsy, share knowledge, and improve care. The International Bureau for Epilepsy (IBE) was established in 1961 to study the medical and nonmedical aspects of epilepsy. In 1966, the surgeon general of the United States created the Public Health Service Advisory Committee on the Epilepsies.
The International League Against Epilepsy took a leadership role in 1969 when it accepted the first “Clinical and electroencephalographic classification of epileptic seizures” at its General Assembly in New York. The new standards created common terminology for epilepsy. A shared set of terminology facilitated improved communication and information-sharing among researchers and physicians. Those original classifications were updated in 1981 and 1989 before the most recent update in 2017.