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).