Neuroblastoma found in a 4-year-old after rituximab therapy for opsoclonus-myoclonus.

Opsoclonus-myoclonus, a rare paraneoplastic syndrome that may occur in patients with neuroblastoma, is thought to be a humorally mediated immune reaction to malignant cells that cross-react with autoantigens. This report describes the case of an occult neuroblastoma diagnosed in a 4-year-old female 2 years after presentation of opsoclonus-myoclonus. Although no mass was evident on previous imaging at an interval of 10 months, a computed tomographic scan 4 months after rituximab treatment and 20 months after presentation revealed a new left adrenal mass. Although neuroblastomas can be identified months after presentation of opsoclonus-myoclonus without treatment with rituximab, this report describes one of the longest intervals using up-to-date imaging techniques. Therefore the case raises two concerns: (1) whether the same immune process that causes opsoclonus-myoclonus may suppress neuroblastomas, and (2) whether immunosuppressive therapy with rituximab may inhibit the immune reaction to occult neuroblastomas in patients with unexplained opsoclonus-myoclonus.