Woman with Breast Cancer Presenting with Opsoclonus–Myoclonus Syndrome: A Case Report and Literature Review

Opsoclonus-myoclonus syndrome (OMS) is rarely associated with breast cancer. This paraneoplastic syndrome poses significant diagnostic and therapeutic challenges for physicians. This paper discusses a case of a 58-year-old Caucasian woman with complex neurological symptoms identified as paraneoplastic OMS due to non-metastatic breast carcinoma. This autoimmune disorder is associated with onco-neural autoantibodies, precisely type II anti-Ri nuclear antibody (ANNA-2), which targets the intracellular Ri antigen (Ri-PNS) and cross-reacts with two neuron-specific antigens. A multidisciplinary approach involving neurologists played a crucial role in case management. Left breast biopsy revealed a poorly differentiated ductal infiltrating carcinoma of the left breast, with 95% positive estrogen receptors, 12% positive progesterone receptors, HER-2 1+, FISH not amplified, and Ki67 at 50%. The patient underwent quadrant surgery for breast cancer and received hormonal therapy with anastrozole. To date, the patient is cancer-free, but OMS persists. Neurological treatment did not yield significant or durable results. In conclusion, the medical literature on OMS in patients with breast cancer is fragmented. This report illustrates the complexity of managing breast cancer patients with OMS and reinforces the critical need for a multidisciplinary approach.