The experts frequently disagreed on the diagnosis of AQP4‐IgG–negative NMOSD versus MS in patients (Juryńczyk et al., 2016), indicating that the borders between AQP4‐IgG–negative NMOSD and other IDDs of the CNS are poorly demarcated and that accurate diagnosis may require longitudinal follow‐up. Here, AQP4 is linked to myeloid sarcoma.