RESUMEN
BACKGROUND: Neuromyelitis optica leads to severe disability. Preventive treatment includes steroids and immunosuppressants, and indications are based on retrospective and observational studies. METHODS: We analyzed 158 patients with neuromyelitis optica regarding disease course, prognostic factors, and treatment response to azathioprine, a widely available low-cost drug. Disability accumulation was used as an endpoint to treatment response. RESULTS: Eight patients with monophasic and 150 with relapsing disease with a median 7 years of disease duration and 4.6 years of follow-up were evaluated. All relapsing patients received preventive treatment, 100 with azathioprine. Only 30% reached Expanded Disability Status Scale (EDSS) 6, and 69% of patients presented no disability accumulation along follow-up. The time under azathioprine and prednisone use were inversely correlated to the hazard of disability accumulation (hazard ratio (HR) = 0.981 and 0.986, respectively; p < 0.01). Each month under azathioprine use reduced disability accumulation by 2.6% (HR = 0.974, p < 0.01), corresponding to an 80% decrease in EDSS progression over 5 years. INTERPRETATION: We report less disability accumulation than previous series on patients with neuromyelitis optica, two-thirds presenting no disability accumulation along follow-up. Continued azathioprine used from early disease onset was strongly associated to maintenance of neurological function and should be offered as a viable option for low-income scenarios.