The incidence and prevalence of neuromyelitis optica: a systematic review

Interest in neuromyelitis optica (NMO) has increased substantially over the last few years, but it is not known whether NMO has the same geographic and temporal variations in disease risk as multiple sclerosis (MS). We aimed to evaluate the worldwide incidence and prevalence of NMO through a systematic review of published peer-reviewed studies. We performed a search of the English-language literature using MEDLINE and EMBASE from January 1985 to March 2012. Search terms included "neuromyelitis optica," "Devic's," "opticospinal," "incidence," "prevalence," and "epidemiology." We assessed study quality using a standardized instrument. A total of five studies met the inclusion criteria. Three of the studies were from North America, and all studies were published between 2005 and 2012. All studies were of good quality, but only one study reported standardized rates, and subgroup-specific estimates were rarely reported. The incidence of NMO per 100,000 population ranged from 0.053 to 0.40, while the prevalence per 100,000 population ranged from 0.52 to 4.4. Heterogeneity was high among the incidence (I(2) = 68.0%) and prevalence studies (I(2) = 94.0%). This review highlights the limited knowledge regarding the epidemiology of NMO and the importance of obtaining estimates standardized to common populations to enhance comparability of studies from different jurisdictions. Future studies would also benefit from reporting age-, sex-, and race- or ethnicity-specific estimates.