Opsoclonus-myoclonus syndrome (also known as dancing eyes- dancing feet syndrome) is a rare disease of inflammatory, parainfectious, paraneoplastic or idiopathic nature consisting of neurologic and behavioral disorders.
Opsoclonus-myoclonus syndrome usually sets in abruptly and can become chronic; remission and relapses have also been described, with motor, cognitive and behavioral impairment. The disease usually affects children between 1 and 3 years of age, but adult onset has also been reported. The ataxia can appear in a subacute manner, over several weeks, making the diagnosis more difficult, as opsoclonus usually appears later.
Symptoms consist of opsoclonus, myoclonus, ataxia, irritability, dysarthria or mutism, hypotonia, vomiting , head tilt, excessive drooling, malaise, incoordination, cranial nerve palsies, seizures and sleep disturbances . Encephalopathy manifests as slow ideation and mood changes.
Opsoclonus is characterized by spontaneous, arrhythmic, conjugate saccades of the eyes, that might initially manifest as ocular flutter. Symptoms persist during sleep.
Myoclonus represents involuntary, brief movements caused by muscular contractions or inhibitions, involving the face, eyelids, limbs, fingers, head and trunk. It may make sitting or standing impossible and becomes worse when the patient is agitated.
Opsoclonus-myoclonus syndrome is usually associated with neuroblastoma in children  and small-cell lung cancer or breast adenocarcinoma in adults. Other conditions that should be excluded are melanoma , gynecologic malignancies , urologic cancers , hematologic  and gastrointestinal neoplasms.
The main tool for establishing this diagnosis is a clinical examination, with careful observation of symptoms described above. If tumors are suspected, computer tomography scans of the neck, chest, abdomen and pelvis, as well as iodine-123-meta-iodobenzylguanidine scintigraphic scans should be performed in children, whereas adults benefit from positron emission tomography.
Laboratory workup includes oligoclonal bands, lymphocyte subset analysis showing a high number of CSF B cells, studies of cytokines and chemokines and autoantibody 9Hu antineuronal nuclear antibodies. Although autoantibody testing is not routinely recommended, tests for autoantibodies directed against cerebellar Purkinje cells as well as peripheral nerve axons can be performed  , in addition to the routine complete blood cell count. Other autoantibodies that have been described in this context are: neuronal nuclear antigens  , anti-neuronal calcium channels  , N-methyl-D-aspartate receptor   and ANNA-2 autoantibodies.
The presence of an infectious etiology should also be established (Epstein-Barr virus, cytomegalovirus, rickettsial infection, mycoplasma, Whipple disease, herpes simplex virus, varicella zoster virus and human immunodeficiency virus). Furthermore, the clinician should keep in mind that cases have also been described in association with hyperosmolar nonketotic diabetic coma and cocaine ingestion. If tests fail to demonstrate a neoplastic or infectious etiology, an autoimmune reaction against central nervous system tissues should be suspected.
If a spinal puncture is performed, one can expect to find higher amounts of B cells in the cerebrospinal fluid of opsoclonus-myoclonus syndrome patients, probably in a neuroinflammatory context .