Opsoclonus myoclonus syndrome (OMS), also known as opsoclonus-myoclonus-ataxia (OMA), is a rare neurological disorder of unknown cause which appears to be the result of an autoimmune process involving the nervous system.

[citation needed] It is hypothesized that a viral infection (perhaps St. Louis encephalitis, Chikungunya, Epstein-Barr, Coxsackie B, enterovirus, or just a flu) causes the remaining cases, though a direct connection has not been proven.

[17] Involvement of local lymph nodes is common, but these children rarely have distant metastases and their prognosis, in terms of direct morbidity and mortality effects from the tumor, is excellent.

[22] Viral infection may play a role in the reactivation of disease in some patients who had previously experienced remission, possibly by expanding the memory B cell population.

[23] Studies have generally asserted that 70-80% of children with OMS will have long-term neurologic, cognitive, behavioral, developmental, and academic impairment.

Since neurologic and developmental difficulties have not been reported as a consequence of neuroblastoma or its treatment, it is thought that these are exclusively due to the immune mechanism underlying OMS.

[24] One study concludes that: "Patients with OMA and neuroblastoma have excellent survival but a high risk of neurologic sequelae.