Abstract
We herein report a 52-year-old woman with anti-aquaporin 4 antibody-positive neuromyelitis optica spectrum disorder (NMOSD) and idiopathic multicentric Castleman disease (iMCD) who was successfully treated with tocilizumab, a humanized anti-human interleukin (IL)-6 receptor monoclonal antibody. This is the first report of a case of coexisting NMOSD and iMCD. IL-6 is involved in the pathogenesis of both NMOSD and iMCD, and tocilizumab is effective against both diseases. By treating the patient with tocilizumab, the lung lesions due to iMCD improved, and the neurological symptoms of NMOSD did not recur.