Clinical features of three cases of neurosarcoidosis with a positive aquaporin-4 antibody requiring differentiation from neuromyelitis optica spectrum disorder.

We report three cases of neurosarcoidosis presenting with optic neuritis or myelitis that required differentiation from neuromyelitis optica spectrum disorder (NMOSD) due to positive aquaporin-4 antibody (AQP4-Ab) results. Positive AQP4-Ab findings were identified using a cell-based assay (CBA) in one case and enzyme-linked immunosorbent assay (ELISA) in two cases. The positive results obtained by CBA were considered to represent either latent positivity or false positives, whereas all positive results obtained by ELISA were regarded as false positives. All cases showed elevated soluble interleukin-2 receptor levels in both the serum and cerebrospinal fluid, as well as enlarged mediastinal and hilar lymph nodes. One patient responded poorly to biological monotherapies including ravulizumab. Positive AQP4-Ab results caused by neurosarcoidosis should be considered in cases with features that are atypical for NMOSD.