Anti-Ri-Antibody-Associated Paraneoplastic Syndrome in a Man with Breast Cancer Showing a Reversible Pontine Lesion on MRI

BACKGROUND Paraneoplastic neurological disorders associated with anti-Ri-antibodies, which are typically present with opsoclonus-myoclonus-ataxia. Most cases with anti-Ri-antibodyassociated paraneoplastic syndrome due to breast cancer occur in women - its occurrence in men is extremely rare. CASE REPORT We present herein the case of a male patient with breast cancer who had atypical anti-Ri-antibody-associated paraneoplastic syndrome presenting as complete horizontal ophthalmoplegia, left trigeminal sensory symptoms, and truncal ataxia. Following the diagnosis of paraneoplastic syndrome, chemotherapy and immunomodulating treatment including intravenous immunoglobulin and oral prednisolone were administered. Although the patient was negative for serum anti-Ri-antibodies 14 weeks later, his symptoms persisted. CONCLUSIONS To our knowledge, this is the first case report of ophthalmoplegia without opsoclonus-myoclonus in a male anti-Ri-antibody-positive patient with breast cancer.