High-Risk Neuroblastoma Presenting After Completion of Treatment for Opsoclonus Myoclonus Ataxia Syndrome: A Case Report

A 17-month-old boy presented with fever, ataxia, and opsoclonus. Past medical history revealed benign familial infantile seizures secondary to a germline SCN2A mutation. A diagnosis of opsoclonus myoclonus ataxia syndrome (OMAS) was made. Investigations showed a 4-cm right paravertebral spinal mass, but biopsy was normal. Repeat magnetic resonance imaging (MRI) scan 4 months after commencing steroids showed no evidence of a mass, and symptoms subsided with pulsed dexamethasone for 12 months. He re-presented 3 years later with back pain, and a computed tomography (CT) scan showed an 11-cm right paravertebral mass and pleural effusion. Biopsy confirmed metastatic high-risk neuroblastoma (HR-NB). Multimodal treatment was started. The patient is now 4 years off treatment and remains in complete remission. Neuroblastoma is the second commonest childhood solid tumour and associated with OMAS in 1% to 2% of cases. To our knowledge, this is the first case of HR-NB following treatment for OMAS. Whether the tumour spontaneously regressed and then recurred is unclear, as is the significance of the SCN2A mutation. We recommend continued surveillance imaging for neuroblastoma in cases of OMAS, on at least 2 occasions even if a biopsy is initially negative and subsequent imaging normal.