Cerebellar Hypoplasia and Treatment Course of a Two-Month-Old Infant With KCNQ2 Epileptic Encephalopathy Due to a De Novo Variant and Review of the Literature

In this paper, we report the treatment course, magnetic resonance imaging (MRI), and electroencephalography (EEG) findings of a two-month-old girl with KCNQ2 epileptic encephalopathy caused by a de novo variant. The patient started having seizures 2 days postnatally. Despite treatment with phenobarbital, phenytoin, levetiracetam, topiramate, clonazepam, vigabatrin, clobazam, and pyridoxine, she continued to have 10 or more seizures per day. EEG recordings showed multifocal epileptiform discharges with diffuse background slowing. MRI revealed left cerebellar hypoplasia. After lacosamide administration, the severity and frequency of seizures decreased by 80%. EEG recordings showed a significant improvement. A de novo heterozygous variant of c.1681C>A (p.Pro561Thr) in the KCNQ2 gene was detected. After carbamazepine add-on treatment, the patient achieved seizure-free status for about 2 years. This case demonstrates the efficacy of lacosamide against KCNQ2 epileptic encephalopathy. To our knowledge, this is the first report to document the association between cerebellar hypoplasia and KCNQ2 variants.