Subcortical band heterotopia: electroclinical, radiological, and prognostic features in adults

Subcortical band heterotopia (SBH) is a neuronal migration disorder within the agyria-pachygyria spectrum, ranging from subtle thin bands to diffuse lissencephaly. Adult presentations and prognostic factors remain poorly defined.

To characterize the clinical, electrophysiological, radiological features, and long-term outcomes of adults with epilepsy and SBH.

We retrospectively reviewed 16 adults diagnosed between 2000 and 2024. Demographics (including age at seizure onset), epilepsy risk factors, seizure semiology, treatment histories, and follow-up durations were obtained from hospital records. Interictal and ictal EEG data were gathered from epilepsy center archives and PACS, and MRI studies were analyzed for lesion distribution.

All 16 patients (12 females; mean age 40 years, range 25-55) remained alive at last follow-up. Seizure onset occurred between 6 months and 15 years of age. Developmental delay was noted in 7 patients (44%). All exhibited pharmacoresistant epilepsy. Interictal EEGs demonstrated focal (predominantly temporal in 11/16, 69%), multifocal, combined focal/multifocal, and generalized epileptiform discharges. Seven underwent video-EEG monitoring, revealing predominantly extratemporal seizure semiology in 6/7 (86%). Levetiracetam and carbamazepine were the most frequently employed antiseizure medications. Four patients received vagus nerve stimulation for drop attacks and generalized seizures; three experienced ≥ 50% seizure reduction.

The SBH in adults typically manifests as refractory focal epilepsy with frequent developmental delays. Given the absence of pathognomonic semiology, comprehensive evaluation-including multimodal EEG, high-resolution neuroimaging, and genetic testing when available-is essential for accurate diagnosis and tailored management.