Opsoclonus-Myoclonus With Anti-YO Antibodies Revealing Breast Cancer: A Case Report.

Opsoclonus myoclonus syndrome (OMS) is a rare neurological disorder characterized by irregular, continuous, and chaotic eye saccades accompanied by myoclonus, defined by brief, shock-like muscle spasms in the arms or legs. This syndrome often presents with additional features such as cerebellar syndrome, nycthemeral rhythm disorders, hallucinosis, and irritability-type behavioral disorders. In adults, OMS is predominantly paraneoplastic, necessitating screening for onconeural antibodies (ONA). While specific medications for OMS are lacking, addressing the underlying cause may ameliorate its clinical manifestations. The presence of opsoclonus-myoclonus should prompt urgent and thorough investigation for an underlying cancer, given its frequent association with paraneoplastic neurological syndrome (PNS). Here, we present the case of a 39-year-old patient with opsoclonus associated with cerebellar ataxia, revealing a breast neoplasm with positive anti-YO antibodies. Through the review of the literature, we discuss the epidemiological, clinical, diagnostic, and therapeutic aspects of this rare situation.