We report a rare case of paraneoplastic neurological syndrome (PNS) with dual seropositivity of anti-aquaporin-4 (AQP-4) and myelin oligodendrocyte glycoprotein (MOG) antibodies in a 40 year-old lady with metastatic triple negative breast cancer.

Our patient received multiple lines of anti-neoplastic treatment including immunotherapy with pembrolizumab as well as chemotherapy with taxol, carboplatin, gemcitabine, capecitabine, cytoxan, sacituzumab and nevalbine for triple negative breast cancer. Meningoencephalomyelitis developed 2 years after diagnosis of breast cancer and 1 year after discontinuation of immunotherapy with pembrolizumab. She first developed longitudinally extending transverse myelitis extending from T11-12 that symptomatically improved with high dose intravenous methylprednisolone. One month later she developed left optic neuritis and meningoencephalitis with new enhancing lesions in the brain and spinal leptomeninges. Differential diagnosis included metastatic disease and PNS. Cerebrospinal fluid (CSF) analysis during both episodes revealed normal glucose, protein, elevated white blood cell count. Cytology was negative for malignancy. CSF was positive for neuromyelitis optica (NMO) IgG antibody APQ-4 and autoimmune myelopathy panel was positive for MOG antibody. She was thus diagnosed with paraneoplastic neurological syndrome, and had significant clinical and radiographic improvement after completion of plasmapheresis and intravenous immunoglobulin. There was resolution of pleocytosis on repeat CSF testing. She did not have recurrence PNS with maintenance rituximab every six months and daily low dose prednisone. She succumbed to progressive systemic metastatic disease 4.5 years after her breast cancer diagnosis.

We highlight the importance of testing for paraneoplastic etiology in cancer patients with radiographic menigoencephalomyelitis or meningitis with atypical symptoms of meningeal carcinomatosis and/or CSF profile negative for leptomeningeal carcinomatosis. This case demonstrates that these antibodies can occur concurrently and cause clinical features of both neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody disease (MOGAD) in a patient with a singular type of cancer.