Opsoclonus-Myoclonus Syndrome (OMS)

Clinical features

• Opsoclonus: rapid, involuntary, chaotic, conjugate eye movements in multiple directions
• Myoclonus: brief, irregular jerks of the limbs, trunk, or head
• Ataxia: unsteady gait, falls, poor coordination
• Irritability, behavioral regression, and sleep disturbance
• Speech and developmental regression may occur in children

1. Opsoclonus
2. Ataxia and/or myoclonus
3. Behavioral change and/or sleep disturbance
4. Neuroblastoma

Causes

• Children: often paraneoplastic, most commonly associated with neuroblastoma or ganglioneuroblastoma
• Postinfectious or idiopathic immune-mediated disease
• Adults: may be associated with malignancy, particularly small-cell lung cancer or breast/gynecologic tumors, often with anti-Ri antibodies
• Drugs and toxins are uncommon but recognized causes

Investigations

• Neurologic examination and assessment of severity
• MRI brain, mainly to exclude structural disease
• Screening for neuroblastoma in children:
  • Urine catecholamine metabolites, VMA/HVA
  • Abdominal imaging and whole-body imaging such as MIBG scan, according to local protocol
• CSF studies and autoimmune/paraneoplastic antibody testing when appropriate
• Developmental, neuropsychological, behavioral, and sleep assessment

Treatment

• Treat an underlying tumor if present, usually surgical removal for localized neuroblastoma
• Early immunotherapy, often:
  • Corticosteroids, such as high-dose IV methylprednisolone or oral prednisolone/dexamethasone
  • IV immunoglobulin (IVIG)
  • Rituximab in severe, relapsing, or refractory disease
  • Cyclophosphamide may be considered in selected resistant cases
• Physiotherapy, occupational therapy, speech therapy, and developmental support
• Long-term follow-up for relapse, cognitive impairment, behavior problems, and learning difficulties

Prognosis