Prolonged Diagnostic Latency and Long-term Surveillance in Anti-Ri Antibody-positive Opsoclonus-myoclonus Syndrome with Carcinoma of Unknown Primary.

Opsoclonus-myoclonus syndrome (OMS) is a rare paraneoplastic neurological disorder that is usually associated with breast cancer or small-cell lung carcinoma. We report the case of a 71-year-old woman with anti-Ri antibody-positive OMS, in whom no malignancy was initially identified. Thirty months later, carcinoma of an unknown primary tumor with supraclavicular and liver metastases was diagnosed. Neurological symptoms remained stable with immunosuppressive therapy, but the overall outcome was poor owing to progressive malignancy. This case underscores the fact that neurological stability does not necessarily equate to a favorable prognosis, and highlights the need for long-term surveillance in cases involving paraneoplastic syndromes.