A pediatric case of clinically isolated syndrome presenting with one-and-a-half syndrome

Background

One-and-a-half (OAAH) syndrome is defined as complete horizontal gaze palsy in one eye and medial gaze palsy in the other, while binocular convergence remains intact. This syndrome arises from concurrent damage to the unilateral medial longitudinal fasciculus and either the paramedian pontine reticular formation or abducens nerve nucleus within the pontine tegmentum.

Case presentation

A 7-year-old girl presented with acute onset nausea, vomiting, diplopia, and exotropia, occurring 4 weeks after influenza vaccination. Examination revealed preserved vertical gaze bilaterally with complete horizontal gaze palsy in the right eye and isolated adduction deficit in the left eye, while convergence remained intact. Neurological examination was otherwise unremarkable. Brain magnetic resonance imaging (MRI) demonstrated high signal intensity lesions in the pontine tegmentum, medulla oblongata, and cerebral white matter without gadolinium enhancement. Treatment with prednisolone rapidly resolved oculomotor deficits, and the patient remained asymptomatic with no new MRI lesions at 1 year follow-up.

Discussion

The patient was diagnosed with isolated OAAH syndrome. The cause was considered as clinically isolated syndrome (CIS) based on demyelinating changes on MRI in the region associated with OAAH syndrome and not meeting the criteria for acute disseminated encephalomyelitis or multiple sclerosis (MS). Isolated OAAH syndrome in the pediatric population is uncommon, with few case reports, including a case of MS. Furthermore, the association between influenza vaccinations and CIS remains unclear.

Conclusion

We reported a case of isolated OAAH syndrome caused by CIS in a pediatric population.