To conduct external validation of previously published epilepsy surgery prediction
tools using a large independent multicenter dataset and to assess whether these tools
can stratify patients for being operated and for becoming free of disabling seizures
(ILAE 1 and 2).We analyzed a dataset of 1,562 patients, not used for tool development.
We applied two scales: Epilepsy Surgery Grading Scale (ESGS) and Seizure Freedom Score
(SFS), and two versions of Epilepsy Surgery Nomograms (ESNs): the original version
and the modified version which included EEG data. For the ESNs we used calibration
curves and concordance indexes. We stratified the patients into three tiers, for assessing
the chances of attaining freedom of disabling seizures after surgery: high (ESGS 1,
SFS 3-4, ESNs>70%), moderate (ESGS 2, SFS 2, ESNs 40-70%) and low (ESGS 2, SFS 0-1,
ESNs<40%). We compared the three tiers as stratified by these tools, concerning the
proportion of patients who were operated, and for the proportion of patients who became
free of disabling seizures.The concordance indexes for the various versions of the
nomograms were between 0.56 and 0.69. Both scales (ESGS, SFS) and nomograms accurately
stratified the patients for becoming free of disabling seizures, with significant
differences among the three tiers (p<0.05). In addition, ESGS and the modified ESN
accurately stratified the patients for having been offered surgery, with significant
difference among the three tiers (p<0.05).ESGS and the modified ESN (at thresholds
of 40% and 70%) stratify patients undergoing presurgical evaluation into three tiers,
with high, moderate and low chance for favorable outcome, with significant differences
between the groups concerning having surgery and becoming free of disabling seizures.
Stratifying patients for epilepsy surgery has the potential to help select the optimal
candidates in underprivileged areas and better allocation of resources in developed
countries.
