Introducing the Epilepsy Surgery Nomogram: An Unprecedented Tool for Individualized Outcomes Prediction

By Lara Jehi, MD

Brain surgery is the only available curative option for drug-resistant focal epilepsy, but identifying good surgical candidates remains a major challenge. While many patients who could benefit from this procedure are missed and never referred for surgical evaluation, others see multiple specialists and undergo highly complex evaluations before realizing that epilepsy surgery is inappropriate for them. The crux of the problem is the healthcare community’s inability to adequately predict the outcomes of epilepsy surgery, which prevents us from optimally targeting the application of this potentially lifesaving intervention.

Attempt at a comprehensive tool for individualized prediction

In an unprecedented effort to address this prognostication conundrum, Cleveland Clinic’s Epilepsy Center led an international collaboration of major epilepsy centers in the U.S., France, Italy and Brazil to develop a novel statistical tool that we call the Epilepsy Surgery Nomogram (ESN). This simple nomogram, available here, uses six clinical patient characteristics (see below) and provides an objective, individualized prediction of postoperative seizure outcomes. Our nomogram and its initial retrospective validation were recently described in Lancet Neurology.

Defining the need

To understand the innovative value of the ESN, it’s helpful to trace the path by which patients currently get to the point of having brain surgery for epilepsy:

• Step 1: The community neurologist recognizes that a patient’s epilepsy is drug-resistant.
• Step 2: The community neurologist refers the patient to a comprehensive epilepsy center for more specialized treatment options, including brain surgery.
• Step 3: At the comprehensive epilepsy center, the patient undergoes extensive testing, the results of which are discussed in a multidisciplinary patient management conference where experts reach a consensus recommendation to operate or not based on their subjective interpretation of the available data.
• Step 4: The chances of surgical success (seizure freedom) are provided to the patient based on the compiled rates of seizure freedom from large published surgical cohorts.

This bird’s-eye view of the typical current path to epilepsy surgery reveals the unquestionable need for process improvements that could be fostered by a tool like the ESN.

Limits of current practice

Determining drug resistance (Step 1 above) is now facilitated by clear guidelines from the International League Against Epilepsy, which define drug resistance as failure of sustained seizure control following adequate use of two appropriate antiepileptic medications. In contrast, all the subsequent steps of the path above are currently highly subjective.

For instance, the referral decision is driven by many factors, including the local neurologist’s coarsely estimated risk-vs.-benefit calculation regarding possible brain surgery. Yet recent data show a knowledge gap that often leads to overestimation of risks in this calculation, preventing many potentially good candidates from getting the appropriate surgical treatment.

Additionally, even when a patient is seen in a tertiary care center, various specialists may interpret his or her clinical picture differently. This is understandable, given that the value of any given test in guiding patient care up to that point has essentially been studied in relation to the prognostic value of the test in isolation rather than in the general clinical context.

‘What about patients like me?’

Based on the current medical literature, a physician can find that test A predicts an X percent chance of postoperative seizure freedom, test B predicts a Y percent chance and so on. The ideal scenario, in which all tests are aligned, with little variation between X and Y, happens in less than one-third of cases, as our group recently demonstrated. This means the remaining two-thirds of patients fall into a limbo where nobody knows exactly how well surgery will fare in controlling their seizures.

That’s why physicians often cite numbers reflecting how often all patients who had epilepsy surgery became seizure-free. While these are helpful data, what a patient needs to know is how the surgery will affect him or her, rather than the hundreds of strangers who had the procedure done. “How did patients like me do?” is the question they care about far more than “How well does this work in general?”

Enter the Epilepsy Surgery Nomogram

In this context, we developed the ESN to meet these needs for more objective prognostication, more scientific decision-making and more individualized patient counseling. Community neurologists may use the ESN to better inform their initial estimates of potential surgical success, and specialized epileptologists can use it to provide individualized patient counseling.

Its potential is huge, considering the possibility of infinite improvements through incorporation of additional outcome determinants from imaging or electrophysiologic data — work that our team currently has underway.

The ESN is a Web-based (Figure), user-friendly, clinically driven tool that uses the following six easily defined variables to estimate the likelihood of seizure freedom at two and five years after epilepsy surgery:

• Age
• Gender
• Seizure frequency
• Presence/absence of convulsions
• Epilepsy etiology
• Expected broad localization

Figure. Screenshots of the Web-based Epilepsy Surgery Nomogram. The top image shows fields where the provider enters patient-specific data for the six required variables. The bottom image shows how the patient-specific surgical outcome predictions are displayed. The online risk calculator is available at clevelandclinic.org/epilepsycalculator.

First proof of concept for individualized outcomes assessment

The ESN was developed after a careful analysis of 846 patients who underwent epilepsy surgery at Cleveland Clinic over an 18-year period. It was then tested in a retrospective external validation cohort of 604 patients operated on over a similar period at Mayo Clinic; the University of Campinas in Brazil; the Ospedale Niguarda surgery program in Milan, Italy; and two hospitals in Marseilles, France. It performed reasonably well, as reported in our recent paper, and provided the first-ever proof of concept that individualized outcome prediction is possible in epilepsy surgery. Next steps include prospective validation studies.

From educated opinion to science

Physicians learn tremendously from personal experience, but such experience is still limited to the relatively small number of patients an individual physician has treated. The ESN allows us to bring patient counseling into the 21st century and expand it beyond our best “educated opinion” to actual science. Our patients deserve it.

Dr. Jehi is Head of the Outcomes Research Group and Director of Clinical Research in Cleveland Clinic’s Epilepsy Center.