Neuromyelitis optica (NMO) is an inflammatory demyelinating autoimmune disease with severe, tremendously incapacitating, consequences in the patient's health and wellbeing. Until 2004, NMO was considered a restricted type of multiple sclerosis but in the same year an auto-antibody reacting against aquaporin-4 (NMO-IgG) was found to be related with NMO and it was considered the main etiologic agent of this disease. Its detection is very sensitive and specific allowing an early diagnosis and a better treatment and prognosis. With this tool, a spectrum of diseases including other autoimmune diseases was found to have NMO-IgG antibodies and a new classification named NMO spectrum disorders was created. In this review, we sum up the developments in this field associated with other autoimmune diseases. We approach the latest discoveries in the diagnosis like the new biomarkers that will possibly be used in the close future or the developments in the neuroimaging techniques. We reviewed the literature and synthesized case reports of NMO patients with concurrent autoimmune diseases and the information from useful larger studies. Finally, we summarize the commonly used treatments in NMO and we try to specify the best treatment for NMO with simultaneous autoimmune disease. This review updates the information about this issue and raises the awareness of rheumatologists for these severe diseases.