Neuromyelitis optica spectrum disorder (NMOSD)
A combination of ON and/or myelitis is a common clinical phenotype of NMOSD. Neuromyelitis optica (NMO) was traditionally characterised by recurrent uni- or bilateral ON and TM, and was later expanded to a broader spectrum with restricted or extended forms including brainstem syndromes, referred to NMOSD (12,48,49). Around one-third of AQP4-IgG negative NMOSD patients harbour IgG serum autoantibodies against MOG (12,50). NMOSD as the presenting phenotype in MOGAD occurs in 5-20% of patients (6,25,51). Therefore, in patients with an optico-spinal phenotype, MOGAD represents an important differential diagnosis to AQP4-NMOSD, especially since the combination of myelitis with ON seems to be more common in MOGAD compared to AQP4-NMOSD (12,51,52). Similar to AQP4-NMOSD, MOGAD can also present with brainstem symptoms including intractable nausea, vomiting and hiccups, described as area postrema syndrome (53). However, the area postrema syndrome is less common in MOGAD (54).