COMPARISON OF 2 CLASSIFICATIONS OF POSTOPERATIVE SEIZURE OUTCOME, ENGEL VS ILAE CLASSIFICATION, FOLLOWING EPILEPSY SURGERY IN ADULTS WITH MEDICALLY REFRACTORY EPILEPSY [P05.086]

Chaohua Yan, James Valeriano, Pittsburgh, PA; Kevin Kelly, Allison Park, PA; Carol Lane, Jack Wilberger, Pittsburgh, PA

The evaluation of long-term seizure control in patients with epilepsy requires the consideration of several factors, including seizure frequency, severity, change in epilepsy symptoms over time, concomitant neurologic disability, and quality of life.1 A consistent, accurate, and easy-to-use clinical rating scale is essential for the assessment of postoperative outcomes following epilepsy surgery. The Engel rating scale, first introduced in 1987, is the most commonly used outcome classification for these patients. Surgical outcomes are rated from Class I to Class IV2,3:

  • 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

Over time it became clear that this scale did not reflect a change in classification over successive years. The International League Against Epilepsy (ILAE) recognized this, and proposed that the outcome class and frequency of postoperative seizures be assessed on an annual basis at the anniversary date of surgery, thus in a more longitudinal rather than cross-sectional manner. The new scale is also designed to address problems with the Engel system including: ambiguity of the meaning of “worthwhile improvement,” problems in dealing with outcomes of patients whose seizures tend to cluster together, and inability to compare results with drug trials.

More recently, the ILAE has introduced its own instrument for postsurgical assessment, in which surgical outcome is rated on a scale from Class 1 to Class 62,4:

  • Class 1: Completely seizure free; no auras
  • Class 1a: Completely seizure free since surgery; no auras
  • Class 2: Only aura, no other seizures
  • Class 3: One to 3 seizure days per year; may have auras
  • Class 4: Four seizure days per year or up to 50% reduction in seizure days from baseline; may have auras
  • Class 5: Less than 50% reduction in number of seizure days from baseline, or an increase in seizure days of up to 100% from baseline
  • Class 6: Increase in number of seizure days from baseline of more than 100%

The Engel and ILAE rating scales are used in research and in clinical practice to evaluate outcomes following epilepsy surgery, but they have not been extensively compared with one another in the same patient population.

In this study, Yan et al used both scales to score clinical outcomes following epilepsy surgery in 99 medically refractory patients who underwent selective anterior temporal lobectomy (ATL) at a single institution between 1986 and 2006. The patients were retrospectively rated on the ILAE scale for yearly follow-up evaluations and at the final visit. The mean duration of follow-up was approximately 8.7 years.

The proportion of patients who were rated as seizure free (Class 1) on the ILAE rating scale declined gradually over time following epilepsy surgery, from 54.3% after 1 year to 43.5% after 5 years and 24% after 10 years. The proportion of patients rated as Class 4 increased from 12.9% at year 1 to 40% after 10 years. Rating of surgery outcome with the Engel scale was similar to that of the ILAE scale after 1 year, with 55.6% of patients classified as Class I. However, the 2 scales diverged after 1 year as ratings on the Engel scale were relatively unchanged over time. The Engel scale was considered by the investigators to be less sensitive to worsening function over 10 years of follow-up.

The investigators concluded that ATL can produce significant improvement in medically refractory patients, and that the ILAE rating scale provided a more sensitive measure of changing seizure severity over time in postoperative patients. More research will be required to understand how these 2 rating scales compare with one another in postoperative patients.

References
1. Spencer SS. Progress in epilepsy research: long-term outcome after epilepsy surgery. Epilepsia. 1996;37:807-813.
2. Schomer DL, Black PM. A 24-year-old woman with intractable seizures: review of surgery for epilepsy. JAMA. 2008;300:2527-2538.
3. Engel J, Van Ness PC, Rasmussen TB, Ojemann LM. Outcome with respect to epileptic seizures. In: Engel J, ed. Surgical Treatment of the Epilepsies. 2nd ed. New York, NY: Raven Press; 1993:609-621.
4. Wieser HG, Blume WT, Fish D, et al. ILAE commission report: proposal for a new classification of outcome with respect to epileptic seizures following epilepsy surgery. Epilepsia. 2001;42:282-286.


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