Tumefactive demyelinating lesion due to neuromyelitis optica spectrum disorder: Successful relapse prevention with eculizumab

Background: Tumefactive demyelinating lesions are rare in multiple sclerosis (MS), and even less frequently seen in NMOSD (neuromyelitis optica spectrum disorder). Case report: A 50-year-old man with large parieto-occipital lesion originally concerning for neoplasm underwent stereotactic brain biopsy. With pathology results and later, positive aquaporin-4 antibody (AQP4), he was subsequently diagnosed with tumefactive demyelinating lesion (TDL) due to AQP4. He was successfully treated with eculizumab. Discussion: Here we demonstrate that eculizumab, a newer agent approved for NMOSD in 2019, can be used successfully for treatment of TDL in NMOSD. As the treatment landscape advances in demyelinating disorders, there should be awareness of the successful use of newer agents in rare clinical presentations.