Palpebral myotonia mimicking intermittent strabismus in a child with SCN4A-related sodium channel myotonia.

INTRODUCTION: Sodium channel myotonia associated with pathogenic SCN4A variants may present with prominent eyelid involvement. In young children, palpebral myotonia can mimic intermittent strabismus or ptosis and confound ocular alignment assessment. METHODS: We report a preschool child with a familial heterozygous SCN4A variant (c.2102 G > A; p. Gly701Asp) referred for suspected intermittent esotropia. Serial pediatric ophthalmology assessments documented high bilateral astigmatism and variable ocular alignment findings. Directed bedside examination was performed during episodes of apparent ocular asymmetry. RESULTS: Examination demonstrated delayed eyelid reopening after sustained forceful closure, intermittently affecting either eye, with preserved ocular motility and no consistent manifest deviation in primary gaze. Neuroimaging and fundus examinations were normal. Recognition of palpebral myotonia reframed the apparent "strabismus" episodes, avoided unnecessary escalation of ophthalmic interventions, and supported appropriate multidisciplinary follow-up. DISCUSSION: Palpebral myotonia is an under-recognized mimic of intermittent strabismus in children with SCN4A-related sodium channel myotonia. Delayed eyelid relaxation after forceful closure represents a simple bedside diagnostic clue that may help distinguish myotonia from true strabismus, ptosis, or ocular motor pathology.