Different responses to interferon beta-1b treatment in patients with neuromyelitis optica and multiple sclerosis

Background: Although the benefit of treatment for relapsing-remitting multiple sclerosis (MS) is firmly established, whether interferon beta-1b (IFNB-1b) therapy is efficacious for neuromyelitis optica (NMO) has been debated. Methods: We reviewed the responses to IFNB-1b treatment in 18 patients with relapsing NMO and compared the results with those from 38 patients with relapsing-remitting MS. We compared clinical characteristics, the annualized relapse rate (ARR) and the probability of being relapse free before and after IFNB-1b treatment in patients with NMO and MS. Results: The proportion of patients with more than 50% increase in the ARR after IFNB-1b treatment was much higher in NMO than in MS (P = 0.046). ARR was significantly lower in patients with MS after IFNB-1b administration than before (P = 0.015), but not in NMO. Kaplan-Meier and log-rank statistical analyses revealed that relapse-free rates were lower in NMO than MS after IFNB-1b treatment (P = 0.032). The analyses also showed lower relapse-free rates during the pre-IFNB-1b treatment period than the post-IFNB-1b treatment period in MS (P < 0.001), but not in NMO. Conclusion: IFNB-1b treatment does not appear to be effective for preventing relapse in NMO likely because of differences between the immune-pathogenesis of NMO and MS.