Abstracts

Rationale: Focal cortical dysplasia (FCD), a malformation of cortical development, is the most common cause of refractory epilepsy, often requiring surgical resection for seizure control. The International League Against Epilepsy proposed a classification system to categorize FCD types based on histopathological features: FCDI, II, and III. In contrast to FCDII, FCDI is less well-characterized, with a limited number of series published. Our study aim is to delineate the clinical, radiologic, and genetic characteristics of FCDI.

Methods: This study was approved by the local institutional research ethics board. We enrolled 21 patients who underwent epilepsy surgery and had a histopathological diagnosis of FCDI. We systematically reviewed charts for clinical data, and neuroimaging for radiological features. Screening for somatic pathogenic variants in SLC35A2, the only gene associated with FCDI, was performed in brain-derived DNA.

Results: Of the total 21 individuals, 12 (57%) were male. The average age of seizure onset was 3.3 years (range: 3 weeks to14 years). All individuals had drug-resistant focal seizures and 18 (85%) were on 2 or more antiepileptic drugs. Average age at surgery was 11.4 years (range: 6 months to 18.5 years) with mean epilepsy duration before surgery of 4.4 years (range: 6 months to 18 years); 6 individuals (28.5%) required two surgeries. Brain MRI revealed cortical dysplasia in 4 (19%), progressive hemispheric volume loss in 2 (9.5%), white matter signal abnormalities in 2 (9.5%), and grey-white matter junction signal abnormalities in 2 (9.5%). Global developmental delay was noted prior to the onset of epilepsy in 10 (47%). Furthermore, intellectual disability was noted in 5 (23%), attention deficit hyperactivity disorder in 7 (33%), learning disability in 6 (28%), language pathology in 13 (6.5%), autistic spectrum disorder in 2 (9%), depression in 3 (14%), anxiety in 4 (19%) and abnormal behavioural in 6 (28%). FCDI involved the temporal lobe in 17 (81%) individuals of our cohort. Of the 15 individuals who underwent a single surgery, 13 (87%) had a monolobar resection, 1 had a hemispherectomy and 1 had a multilobar resection. Among the 6 individuals who underwent 2 surgeries, 4 had a monolobar resection. Overall, post-surgical outcome according to Engel classification was class I/II in 14/21 (67%), and class III/IV was in 7 patients (33%). Screening for somatic pathogenic variants in SLC35A2 in brain-derived DNA is ongoing.

Conclusions: Children with FCDI present with early-onset refractory focal epilepsy and have high prevalence of developmental impairment, often observed prior to seizure onset. In contrast to FCDII, radiologic features in FCDI are heterogeneous, making diagnosis based on neuroimaging challenging. In our cohort, the temporal lobe was the most involved, and 2/3 of children achieved favorable post-surgical outcome according to Engel classification.

Funding: Please list any funding that was received in support of this abstract.: MS holds salary award from the Fonds de Recherche en Santé du Quebec.