Isolated Sixth Cranial Nerve Palsy as the First Presenting Sign of MOG Antibody-Associated Disease in a Three-Year-Old Child.

Background: Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a neurological, autoimmune, demyelinating disorder. Clinical phenotypes differ between adults and children, and MOGAD is more commonly observed in the paediatric population compared to the adult population. Cases of isolated cranial nerve palsies as initial clinical phenotypes of MOGAD are rarely reported in the literature. Here, we report a child who presented with an isolated left sixth cranial nerve palsy as the initial sign of anti-myelin oligodendrocyte glycoprotein antibody associated disease (MOGAD). Method: In this case study, we report on a three-year-old female known to the orthoptic and paediatric ophthalmology services due to an intermittent exotropia. The same child later develops an acute convergent deviation of the left eye preceded by a viral illness with no other systemic symptoms. This case reports on the clinical findings and treatment over a five-year period. Results: Immunological investigations revealed positive oligoclonal bands in CSF but negative in serum. Serology was positive for MOG antibodies. Magnetic Resonance Imaging (MRI) showed acute demyelination in the pons and cerebellum with accompanying lesions in cerebral white matter bilaterally and incidental band heterotropia. The symptomatic lesion was found to be a small plaque in the left lower pons in the intrinsic course of the left sixth cranial nerve, suggestive of acute demyelination. The patient completed a five-day course of intravenous methylprednisolone 30 mg/kg daily, followed by a reducing course of oral prednisolone. Follow up discussion: Although brain stem involvement in MOGAD is common, isolated cranial palsies are rare and are not commonly reported as presenting symptoms in children (Barr