OPSOCLONUS-MYOCLONUS-ATAXIA SYNDROME FOLLOWING A FEBRILE ILLNESS IN A TODDLER: A CASE REPORT

Background: Opsoclonus-myoclonus-ataxia syndrome (OMAS) is a rare, immune-mediated pediatric disorder that may follow neuroblastoma or infection, and has occasionally been reported in temporal proximity to vaccination, though causality with vaccination remains unestablished. Diagnostic delay and relapse on corticosteroid tapering can mask the true course; earlier escalation to combination immunotherapy is associated with better outcome. Clinical description: A 1-year-11-month-old boy developed gait difficulty, speech regression, opsoclonus, generalized tremor, irritability, and sleep disturbance within 10 days of receiving the DPT booster and second doses of measles-rubella and Japanese encephalitis vaccines, having tolerated the primary doses previously. Examination confirmed opsoclonus, truncal ataxia with titubation, and four-limb action tremor. Management: Serial brain MRI, an autoimmune encephalitis panel, abdominal ultrasonography, and whole-body PET-CT were normal, excluding demyelination, encephalitis, and occult neuroblastoma. After relapsing on intermittent oral corticosteroids over six months, he was escalated to intravenous dexamethasone, IVIg, and rituximab, with significant improvement in gait, opsoclonus, and tremor. Conclusion: OMAS should be considered in any toddler with sub-acute opsoclonus, ataxia, and developmental regression, even with a negative autoimmune encephalitis panel. Relapse on tapering should prompt escalation to combination immunotherapy rather than repeated steroid courses.