As most of these patients later developed NMO, various groups have suggested classifying these symptoms—if occurring in the context of AQP4-Ab seropositivity—as ‘high-risk syndromes for NMO’ (HRS) and referring to AQP4-Ab-positive classical NMO and AQP4-Ab-positive HRS as ‘NMO spectrum disorder’ (NMOSD) or ‘autoimmune AQP4 channelopathy’ [74–77]. Here, AQP4 is linked to neuromyelitis optica.