Neuromyelitis optica relapses: race and rate, immunosuppression and impairment

Objective Neuromyelitis optica (NMO) is a rare antibody-mediated CNS disease characterised by disabling relapses leading to high morbidity and mortality. Understanding relapse activity and severity is important for treatment decisions and clinical trial design. We assessed (1) whether clinical and demographic factors associate with different relapse rates and (2) the relative impact of immunosuppressive treatments on relapse rates and on attack-related residual disability. Methods Clinical, demographic and treatment data were prospectively collected from 79 consecutive aquaporin 4 antibody positive patients seen in the nationally commissioned Oxford NMO service. The influence of clinical features on annualised relapse rates (using multiple regression) and the effect of immunosuppression on relapse-associated residual disability for transverse myelitis and optic neuritis attacks (using a mixed effect model) were analysed. Results The mean annualised relapse rate was 0.93. Relapse rates were significantly higher in Afro-Caribbeans, children and in those of shorter disease duration. Relapse rates reduced on treatment (from 0.87 to 0.42). Delay to first treatment did not influence eventual on-treatment relapse rate. Immunosuppressive treatment significantly reduced the residual disability from ON (p<0.01), and TM (p=0.029) attacks. Conclusions Relapse rates in NMO are influenced by multiple factors, including age, ethnicity and disease duration. Current immunosuppressive treatments reduce but do not abolish relapses, however, they appear to additionally lessen the chronic disabling effect of a relapse.