Epileptogenic focal lesions in Dravet syndrome: A warning to investigators

Objective Most patients with Dravet syndrome (DS) have unremarkable neuroimaging studies. However, a small number of patients exhibit focal abnormalities that may modify the epilepsy phenotype. We report a case series of DS patients carrying SCN1A variants concurrent with additional focal brain lesions, aiming to provide details regarding their clinical course, electrographic findings, and imaging features. Methods We reviewed the electronic medical records of patients with developmental and epileptic encephalopathies in our center, from January 2000 to December 2022, identifying 90 patients with DS resulting from SCN1A variants. Of these, patients displaying focal brain lesions were eligible. Results Five patients (4 males and 1 female), with median age of 26 years, were included. All exhibited clinical and electroencephalographic features consistent with the DS spectrum. Sequencing analysis of the SCN1A gene identified pathogenic variants. Magnetic resonance imaging (MRI) revealed focal cortical dysplasia (FCD) in two patients, while the remaining three had cystic lesions. Three patients had previously undergone resective epilepsy surgery in other centers, with no improvement in seizure frequency. Neuropathology studies revealed the presence of FCD type IIA, intracranial teratomas, and dysembryoplastic neuroepithelial tumor (DNET). Significance When an individual with an established diagnosis of genetic epilepsy and a focal lesion on MRI is undergoing preoperative evaluation, it is crucial to conduct a comprehensive analysis to understand the relevance of the focal finding for the patient's phenotype and thus anticipate potential surgical outcomes. In instances where epilepsy in DS patients is influenced by a specific focal structural lesion, resective surgery should be carefully considered after precise pharmacological treatment, acknowledging the persistent influence of an SCN1A variant on expected outcomes.