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To classify postoperative outcomes for epilepsy surgery, Jerome Engel proposed the following scheme, which has become the de facto standard when reporting results in the medical literature:


 * Class I: Free of disabling seizures


 * Class II: Rare disabling seizures ("almost seizure-free")


 * Class III: Worthwhile improvement


 * Class IV: No worthwhile improvement

History
The Engel classification guidelines were devised in 1987 and made public at the 1992 Palm Desert Conference on Epilepsy Surgery. The method was proposed by UCLA Neurologist Jerome Engel Jr.

Overview
In Engel's 1993 summary of the 1992 Palm Desert Conference on Epilepsy Surgery, he annotated his classification system with more detail. The annotation was as follows:


 * Class I: Seizure free or no more than a few early, nondisabling seizures; or seizures upon drug withdrawal only
 * Class II: Disabling seizures occur rarely during a period of at least 2 years; disabling seizures may have been more frequent soon after surgery; nocturnal seizures
 * Class III: Worthwhile improvement; seizure reduction for prolonged periods but less than 2 years
 * Class IV: No worthwhile improvement; some reduction, no reduction, or worsening are possible

Disadvantages
As is the case for all current methods of reviewing epilepsy surgery outcomes, the Engel classification system has subjective components. A disabling seizure is subjective and can vary in definition from person to person. While one epileptic experiencing a seizure when driving a car may find it disabling, the same magnitude of seizure may be interpreted as mild by an epileptic resting in bed. Everything beyond Class I is also subjective because there is no quantitative definition of what qualifies as a rare occurrence. One doctor may consider 2 seizures a year as a rare occurrence while another doctor may consider 5 a year as a rare occurrence. The worthwhileness of the operation is also ambiguous because the worth can be interpreted differently by various patients and healthcare professionals.

The Engel classification system has been thought of as a cross-sectional grading system by medical professionals because it does not account for long term changes in patients. It has been proposed that it would be more beneficial to reevaluate patients on an annual basis, and the International League Against Epilepsy devised a separate rating scale that reevaluates patients on every anniversary of their surgery.