The term NMO was extended to NMOSD in 2015 and those without AQP4 antibodies were set more rigorous requirements so that those with limited anatomical involvement (such as a long spinal cord lesions or severe bilateral optic neuritis (ON)) previously often referred to as NMOSD6 no longer satisfy the 2015 criteria.1 Here, AQP4 is linked to neuromyelitis optica.