To describe the clinical characteristics, treatment, and outcomes of adults with relapse of pediatric-onset paraneoplastic opsoclonus-myoclonus-ataxia syndrome (OMAS).

Paraneoplastic OMAS associated with neuroblastoma is classically described in children. Adult-onset relapses are rare with scarce data.

Patients with pediatric-onset paraneoplastic OMAS seen in the Mayo Clinic Autoimmune Neurology clinic with relapse at age >18 years between 1/2005 and 3/2026 were identified by retrospective chart review.

Case 1: An 18-year-old white female with neuroblastoma-associated OMAS (onset age 15 months) with antineuronal nuclear antibody type-1 antibody (ANNA-1/anti-Hu, titer 1:122,880) and autoimmune epilepsy, developed chronic progressive severe intestinal pseudo-obstruction at age 14 status post subtotal colectomy with end ileostomy requiring total parenteral nutrition, followed by OMAS relapse at age 18. Two years of evaluation for tumor including DOTATATE and FDG PET-CTs did not demonstrate tumor recurrence. She received intravenous methylprednisolone (IVMP) and intravenous immunoglobulin (IVIG) with mild improvement, but had recurrent bowel pseudo-obstruction upon transitioning to mycophenolate mofetil (MMF). Intravenous cyclophosphamide (IVCY) was started for 6 months with significant improvement of oral intake, but her symptoms again worsened with MMF, and rituximab was added. Her opsoclonus and mild ataxia persisted.

Case 2: A 38-year-old white female with paraspinal ganglioneuroblastoma-associated OMAS (onset age 2 years) and Crohn’s disease on ustekinumab developed OMAS relapse with cognitive impairment and mood changes. No tumor was seen on whole body DOTATATE and FDG PET-CT over 2 years of monitoring. Serum and CSF paraneoplastic neural antibody panels were negative. She received IVMP, followed by IVCY for 6 months with near resolution of all symptoms. She was then transitioned to MMF with minimal residual symptoms.

Children with paraneoplastic OMAS due to neuroblastoma/ganglioneuroblastoma may rarely relapse in adulthood despite prior remission and without tumor recurrence, which may implicate a role of memory T cells.