A Rare Case of Neuromyelitis Optica Spectrum Disorders With Unknown Fever and Subacute Cognitive Decline With Normal Images.

We report the case of a 69-year-old Japanese man who came to our hospital with a chief complaint of fever and cognitive decline for three weeks. There were no neurological abnormalities other than the decreased level of consciousness. He developed urinary retention after admission, so we performed a lumbar puncture, although his head and neck magnetic resonance imaging (MRI) showed no abnormal findings. The cerebrospinal fluid (CSF) examination showed albuminocytologic dissociation and the anti-aquaporin 4 antibody was positive. Thus, we diagnosed him with neuromyelitis optica spectrum disorder (NMOSD). NMOSD is an autoimmune disease that causes demyelination. The clue to diagnosing NMOSD is demyelinating findings on MRI. Therefore, it is difficult to diagnose NMOSD if there are no abnormalities on the images. However, abnormal MRI findings are not necessary for the diagnosis of NMOSD. Thus, NMOSD cannot be ruled out even if MRI findings are normal and the real clue to diagnosing NMOSD is the anti-aquaporin 4 antibody.