<qa>  What is the rare immune mediated paraneoplastic syndrome?Opsoclonus-myoclonus ataxia syndrome OMS is a rare immune mediated paraneoplastic syndrome that occurs in approximately 2 to 3 of children with neuroblastoma. Children with neuroblastoma associated opsoclonus-myoclonus tend to have a favorable prognosis from the standpoint of the cure of their cancer. Unfortunately,approximately two-thirds of this subgroup of patients are left with long term sequellae of the syndrome, including residual symptoms of opsoclonus, myoclonus, ataxia, learning difficulties and disturbance of sleep and mood. 