Predictors of azathioprine and mycophenolate mofetil response in patients with neuromyelitis optica spectrum disorder: A cohort study

Background: Relapse rates of 47 % have been reported in patients with neuromyelitis optica (NMOSD) using Azathioprine (AZA) and mycophenolate mofetil (MMF). Prediction of non-responders could help determine which patients are most likely to benefit from newer monoclonal antibody treatments from the outset. Objectives: To identify predictors of AZA and MMF treatment response in NMOSD. Methods: Multicenter cohort study of NMOSD patients from Brazil and the United Kingdom, treated with AZA and MMF. An unsatisfactory response was defined as one severe or two non-severe attacks in a year. Cox regression was used to identify predictive factors of unsatisfactory response to AZA and MMF. Results: 103 NMOSD patients, mean age 38 years, 83% female, and 65% of Black ethnic group were included. An unsatisfactory IS response was observed in 42% of patients over 2.5 years (IQR 1.0-8.8) years. A severe preceding attack was more common in non-responders (31.1% x 76.7%, p = <0.001). In multivariable analysis, severe attack (RR 3.13; 95 % CI 1.37-7.18, p = 0.007) or higher annualized relapse rate (RR 4.84; 95 % CI 2.0111.65, p = < 0.001) predicted an unsatisfactory response. Interestingly, Black NMOSD patients had a lower risk of poor response (RR 0.39, 95 % CI 0.17-0.85, p = 0.019). Conclusion: Severe attack and a higher annualized relapse rate before AZA or MMF initiation were associated with an unsatisfactory IS response. In patients with these characteristics, treatment with higher-efficacy drugs should be considered from the outset.