More recently, anti-AQP4 antibodies have been found also in a subset of patients with isolated transverse myelitis [5], patients with isolated optic neuritis [16], [6], [7], and patients with NMOSD and co-existing CTD [8]–[10], leading to an increase in the number of clinical conditions that require testing for anti-AQP4 antibodies. Here, AQP4 is linked to optic neuritis.