McKeon, Andrew

ObjectiveNeuromyelitis optica (NMO) and its spectrum disorders (NMOSD) are inflammatory demyelinating diseases (IDDs) with a specific biomarker, aquaporin‐4–immunoglobulin G (AQP4‐IgG). Prior NMO/NMOSD epidemiological studies have been limited by lack of AQP4‐IgG seroprevalence assessment, absence of population‐based USA studies, and under‐representation of blacks. To overcome these limitations, we sought to compare NMO/NMOSD seroepidemiology across 2 ethnically divergent populations.MethodsWe performed a population‐based comparative study of the incidence (2003–2011) and prevalence (on December 31, 2011) of NMO/NMOSD and AQP4‐IgG seroincidence and seroprevalence (sera collected in 80–84% of IDD cases) among patients with IDD diagnosis in Olmsted County, Minnesota (82% white [Caucasian]) and Martinique (90% black [Afro‐Caribbean]). AQP4‐IgG was measured by M1 isoform fluorescence‐activated cell‐sorting assays.ResultsThe age‐ and sex‐adjusted incidence (7.3 vs 0.7/1,000,000 person‐years [p < 0.01]) and prevalence (10 vs 3.9/100,000 [p = 0.01]) in Martinique exceeded that in Olmsted County. The AQP4‐IgG age‐ and sex‐adjusted seroincidence (6.5 vs 0.7/1,000,000 person‐years [p < 0.01]) and seroprevalence (7.9 vs 3.3/100,000 [p = 0.04]) were also higher in Martinique than Olmsted County. The ethnicity‐specific prevalence was similar in Martinique and Olmsted County: 11.5 and 13/100,000 in blacks, and 6.1 and 4.0/100,000 in whites, respectively. NMO/NMOSD represented a higher proportion of IDD cases in Martinique than Olmsted County (16% vs 1.4%; p < 0.01). The onset age (median = 35–37 years) and female:male distribution (5–9:1) were similar across both populations; 60% of prevalent cases were either blind in 1 eye, dependent on a gait aid, or both.InterpretationThis study reports the highest prevalence of NMO/NMOSD in any population (10/100,000 in Martinique), estimates it affects 16,000 to 17,000 in the USA (higher than previous predictions), and demonstrates it disproportionately affects blacks. Ann Neurol 2016;79:775–783