Strengths and limitations
epilepsy, seizure, ’
DISORDERS, EPILEPSY
The study included unselected patients from two countries with similar health care systems and follow-up from specialists. The patients were recruited from the Norwegian TSC population and from two regions in Denmark. It is possible that some treated patients invited through the National Centre for Rare Epilepsy-Related Disorders in Norway did not respond to the invitation. Only two invited patients treated with everolimus did not want to participate. Due to equal access to health care services and follow-up from specialists, it is likely that most patients with indications for treatment are known and included. In Denmark, everolimus treatment is centralised, and all treated adult patients from Aarhus University Hospital and all paediatric patients from University Hospital Rigshospitalet were invited. The total response rate in Denmark was high (88%), indicating that the included patients were representative and the risk of selection bias low.Due to the observational design, missing data in medical records and data unconformity were important limitations. Patients’ and parents’ interviews were carried out to reduce this limitation, but potential recall bias could not be excluded. Imaging data were not available for all patients and reduced the sample size. Imaging was reevaluated by experienced radiologists, ensuring data conformity.Due to the irregular (multilobular) shape of most of the SEGAs, the simplified method of volume measurement by multiplying diameters in three orthogonal directions and divided the result by 2 was considered too inaccurate. Despite the chosen method, some inaccuracy in volume measurements may persist due to differences in imaging quality across multiple MRI exams from different centres and over the actual time period.Other ASMs were changed in a majority of the patients, and some underwent epilepsy surgery, which made it difficult to draw conclusions on the cause of the change in seizure frequency. Different conditions for epilepsy treatment between Norway and Denmark were also limitations.