Characteristics and long‐term outcomes of children with confirmed focal cortical dysplasia type 1 after epilepsy surgery: A population‐based study—Authors' reply

We thank Noreen Bux for their interest in our study and for their constructive comments, which raise methodological points we are glad to address. ¹

We fully agree that multivariable regression is the recommended approach for identifying independent predictors in observational research. In our cohort, however, the small number of children with surgically confirmed FCD1 and the correspondingly limited number of recurrence events constrained the number of covariates that could be modeled reliably. Under accepted events‐per‐variable requirements, a multivariable model would have accommodated only one or two predictors and would have carried an evident risk of overfitting and generating unreliable results. ² We therefore reported univariate and descriptive analyses, which we regard as the most responsible treatment of a cohort of this rarity.

We agree that epilepsy surgery practice evolved considerably between 1994 and 2022. ³ We would note, however, that FCD type 1 is a very rare pathology within an already rare cohort of epilepsy surgery patients, accounting for around 3%. ⁴ Dividing such a small cohort across treatment eras would, moreover, have produced subgroups too small to support meaningful comparison.

We are grateful for the suggestion to assess the durability of seizure freedom using time‐to‐event methods, and we consider this the most valuable point raised. Given our median follow‐up of 8.4 years and the delayed relapses observed in several children, Kaplan–Meier estimation is indeed well suited to characterizing the risk of relapse over time and would usefully complement the Engel outcomes reported at last follow‐up. Cox proportional‐hazards regression, by contrast, would be subject to the same events‐per‐variable limitations noted above, and we would caution against overinterpreting a multivariable time‐to‐event model in a cohort of this size. ²

Finally, we share the correspondents' view that future work should address the cost‐effectiveness of early surgery in FCD1 and the development and external validation of individualized prediction models. ⁵ Such efforts will require the larger, ideally multicenter cohorts that no single national cohort can provide, and we hope our data may contribute to those collaborative efforts.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

ETHICAL STATEMENT

We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this report is consistent with those guidelines. The views expressed in this article are solely those of the authors and do not necessarily reflect the official position of Epilepsia Open or the International League Against Epilepsy.

DATA AVAILABILITY STATEMENT

Pseudonymized raw data are personal data according to Finnish law and cannot be shared outside Helsinki University Hospital due to Finnish legislation.