The term opsoclonus refers to a pattern of chaotic, rapid eye movement abnormalities. This sometimes occurs simultaneously with unintentional spasms of muscles in the limbs or trunk (myoclonus). In children, opsoclonus is usually associated with neuroblastoma. In adults, it can be associated with other cancers and with infections. Symptoms usually develop over hours to days. Workup should look for cancer and infection, and if those are found, they should be treated. Whether or not cancer or infection is found, some practitioners will attempt treatment with immunomodulatory therapies. Sometimes, the muscle spasms are treated with antiepileptic medications.