Emergence of lingual dystonia and strabismus in early‐onset SCN8A self‐limiting familial infantile epilepsy

Abstract

AbstractPathogenic variants in SCN8A are associated with a broad phenotypic spectrum, including Self‐Limiting Familial Infantile Epilepsy (SeLFIE), characterized by infancy‐onset age‐related seizures with normal development and cognition. Movement disorders, particularly paroxysmal kinesigenic dyskinesia typically arising after puberty, may represent another core symptom. We present the case of a 1‐year‐old girl with a familial disposition to self‐limiting focal seizures from the maternal side and early‐onset orofacial movement disorders associated with SCN8A‐SeLFIE. Brain MRI was normal. Genetic testing revealed a maternally inherited SCN8A variant [c.4447G > A; p.(Glu1483Lys)]. After the introduction of valproic acid, she promptly achieved seizure control as well as complete remission of strabismus and a significant decrease in episodes of tongue deviation. Family history, genetic findings, and epilepsy phenotype are consistent with SCN8A‐SeLFIE. Movement disorders are an important part of the SCN8A phenotypic spectrum, and this case highlights the novel early‐onset orofacial movement disorders associated with this condition. The episodes of tongue deviation and protrusion suggest focal oromandibular (lingual) dystonia. Additionally, while infantile strabismus or esophoria is a common finding in healthy individuals, our case raises the possibility of an ictal origin of the strabismus. This study underscores the importance of recognizing and addressing movement disorders in SCN8A‐SeLFIE patients, particularly the rare early‐onset orofacial manifestations. It adds to the growing body of knowledge regarding the diverse clinical presentations of SCN8A‐associated disorders and suggests potential avenues for clinical management and further research.