Paraneoplastic opsoclonus–myoclonus syndrome as a rare presentation of breast cancer

Opsoclonus–myoclonus paraneoplastic syndrome is a medical condition that includes opsoclonus along with diffuse or focal body myoclonus and truncal titubation with or without ataxia and other cerebellar signs. This rare neurological syndrome is poorly understood and can result in long-term cognitive, behavioral and motor sequelae. We report a case of a 49-year-old woman with anti-Ri antibody opsoclonus–myoclonus syndrome and an invasive ductal carcinoma with axillary nodes involvement. Following the diagnosis of opsoclonus–myoclonus syndrome, a multimodal immunotherapy treatment, with partial remission of the neurological symptoms. The patient underwent lumpectomy and axillary node dissection and the surgical pathology confirmed the diagnosis of breast cancer stage IIA. This was followed by chemotherapy, radiotherapy and hormone therapy with tamoxifen. At the 6 months follow-up there was a partial improvement, anti-Ri antibody was subsequently reported as negative and there was no evidence of disease recurrence.