Optic neuromyelitis optica, also known as Devic disease, is a severe demyelinating disease of the central nervous system, mainly involving the optic nerve and spinal cord. However, studies now show that NMO and MS are two diseases that differ in clinical manifestations, laboratory tests, immunological pathogenesis and pathological features. In addition, a specific antibody, an autoantibody against aquaporin-4 – called NMO-IgG – can be detected in the blood of the vast majority of NMO patients (Editor’s note: Although theoretically there are many differences between the two In practice, it is not easy to make a correct diagnosis based on each patient’s condition, especially in early or atypical cases of the disease). As research into NMO-IgG has progressed, more patients with diseases similar to optic neuromyelitis optica have been identified, and medical researchers have referred to these diseases collectively as the optic neuromyelitis optica spectrum, which includes: 1) optic neuromyelitis optica; 2) incomplete forms of optic neuromyelitis optica, including those with positive NMO-IgG or AQP4-IgG antibodies: (1) idiopathic solitary or recurrent (2) optic neuritis, especially recurrent optic neuritis, and bilateral optic neuritis of short duration or concurrent onset; (3) many patients with Asian-type optic neuromyelitis optica multiplex as defined by Japanese scholars; (4) optic neuritis associated with systemic autoimmune disease or long-segment (5) optic neuritis or long-segment myelitis with typical foci of NMO in the hypothalamus, peri-lateral ventricles, or brainstem. Note: The above contents are translations of excerpts from professional articles, so please read them with caution to prevent patients and their family members from taking them out of context or randomly taking them into account. What I want to tell you here is that both NMO and MS are difficult to diagnose and require careful screening and differential diagnosis based on clinical symptoms, physical examination (neurological signs), long follow-up of the disease course, MRI, cerebrospinal fluid and other ancillary tests by professional physicians. Some atypical cases are quite difficult to diagnose even for a neurologist like the author of this article.