[From Neuromyelitis Optica to Neuromyelitis Optica Spectrum Disorder: from Clinical Syndrome to Diagnistic Classification]

Neuromyelitis optica spectrum disorder (NMOSD), derived from NMO or Devic's disease, is considered as a distinct disease since the discovery of a novel and pathogenic serum autoantibody targeting aquaporin‑4 (AQP4-IgG) and is distinguished from classical multiple sclerosis (MS). With the continuous extension of knowledge on the clinical manifestations, the previously narrow diagnostic term NMO became NMOSD, which has also been used in the diagnostic criteria since 2015. The current diagnostic criteria enable the early diagnosis of NMOSD in patients with and without AQP4-IgG. Typical clinical manifestations include involvement of the spinal cord, optic nerve and brainstem. Typically patients with the disease also present with neuropathic pain, painful tonic spasms and also other unusual manifestations in NMOSD. Especially in AQP4-IgG positive NMOSD patients, the coexistence with other autoimmune diseases is frequently observed. In most cases NMOSD follows a relapsing course with exacerbation-free periods sometimes lasting years and can be manifested first in advanced adulthood. A subset of AQP4-IgG negative NMOSD patients have been found to harbor autoantibodies targeting myelin oligodendrocyte glycoprotein (MOG), which is considered as a distinct disease entity: these MOG antibody-associated disorders (MOGAD) can present with clinical syndromes resembling both NMOSD and MS and are currently the subject of intensive research.