Neuromyelitis optica spectrum disorder epidemiology and demographics

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes

Overview

• Neuromyelitis optica spectrum disorder (NMOSD) is a rare disease reported worldwide. A 2026 systematic review and meta-analysis of 44 studies from 28 countries found a pooled prevalence of 2.02 per 100,000 persons; individual study estimates ranged from 0.23 to 10 per 100,000 persons.
• Published population-based incidence estimates range from approximately 0.04 to 0.73 per 100,000 person-years. The highest incidence and prevalence in a major systematic review were reported in an Afro-Caribbean population, whereas the lowest were reported in Australia and New Zealand.
• NMOSD most often begins in adulthood and shows a marked female predominance, particularly in aquaporin-4 immunoglobulin G (AQP4-IgG)-positive disease. Nevertheless, NMOSD may begin in childhood or late life and should be considered irrespective of age, sex, race, or ethnicity.
• Geographic and demographic estimates are heterogeneous because studies differ in diagnostic criteria, case ascertainment, access to AQP4-IgG testing, antibody-assay methods, and whether AQP4-IgG-negative cases were distinguished from myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD).

Epidemiology and Demographics

Prevalence

• The pooled worldwide prevalence of NMOSD is approximately 2.02 per 100,000 persons. The wide observed range of 0.23 to 10 per 100,000 persons reflects both genuine geographic and ancestral variation and important differences in study design.
• The 2026 meta-analysis found the highest pooled prevalence in the Americas, followed by Asia, Europe, and Oceania; substantial heterogeneity remained within every region.
• In a contemporary, case-validated Southern California cohort, the overall prevalence in 2019 was 2.55 per 100,000 persons.

Incidence

• Published population-based estimates place the incidence of NMOSD between approximately 0.04 and 0.73 per 100,000 person-years.
• The 2023 recommendations of the Neuromyelitis Optica Study Group (NEMOS) cite incidence estimates of 0.28 to 0.73 per 100,000 person-years among the studies included in their review.
• In the Southern California cohort, the crude overall incidence during 2013–2022 was 0.27 per 100,000 person-years.

Age

• NMOSD may occur at any age, but incidence and prevalence generally peak in middle-aged adults.
• In a large European cohort summarized by NEMOS, the age at onset peaked at approximately 40 years in AQP4-IgG-positive disease and 38.5 years in AQP4-IgG-negative disease.
• Late-onset NMOSD, defined as onset after 60 years of age, accounted for approximately 20% to 28% of incident cases in some mixed-serostatus cohorts; onset after 75 years has also been reported.
• In the contemporary Southern California cohort, the median age at symptom onset was 43.1 years. Pediatric-onset disease before 18 years of age accounted for 6.7% of incident cases, whereas 22.9% were diagnosed at 65 years of age or older. These percentages are cohort-specific and should not be applied as universal population estimates.

Sex

• Females are more commonly affected by NMOSD than males. The female-to-male ratio may reach 10:1 in AQP4-IgG-positive disease and 3:1 in AQP4-IgG-negative disease.
• Among AQP4-IgG-positive patients of reproductive age, the female-to-male ratio may exceed 20:1.
• Female predominance is less marked in AQP4-IgG-negative disease. In the Southern California cohort, 85.7% of incident cases were female, but no female predominance was observed among its small pediatric subgroup.

Race and ethnicity

• NMOSD occurs in all racial and ethnic groups. Population-based studies generally report higher incidence and prevalence among people of African ancestry and lower estimates among White populations, although access to specialist care and antibody testing may contribute to observed differences.
• The table below shows age- and sex-standardized estimates from one rigorously case-validated, multi-ethnic Southern California population. These categories describe the populations recorded in that study and must not be interpreted as deterministic biological classifications.

NMOSD incidence and prevalence by race and ethnicity in a Southern California cohort

Population group	Incidence per 100,000 person-years, 2013–2022 (95% confidence interval)	Prevalence per 100,000 persons, 2019 (95% confidence interval)
Black	0.90 (0.59–1.21)	8.44 (5.52–11.36)
Asian or Pacific Islander	0.32 (0.16–0.48)	2.98 (1.55–4.41)
Hispanic	0.19 (0.13–0.25)	1.88 (1.30–2.47)
White	0.13 (0.07–0.19)	1.03 (0.51–1.55)

Estimates were standardized to the 2020 United States Census population. Adapted from Lee et al., 2025.

Geographic distribution

• NMOSD has been reported worldwide. The highest estimates in the 2021 systematic review were from an Afro-Caribbean population: incidence 0.73 per 100,000 person-years and prevalence 10 per 100,000 persons. The lowest estimates were from Australia and New Zealand: incidence 0.037 per 100,000 person-years and prevalence 0.7 per 100,000 persons.
• The 2026 global meta-analysis found that crude prevalence varied from 0.23 to 10 per 100,000 persons and that the pooled prevalence was highest in the Americas, followed by Asia, Europe, and Oceania.
• No convincing latitude gradient has been established for NMOSD.

Higher-income countries

• Population-based studies from Europe, North America, Asia, and Oceania confirm that NMOSD remains rare, but estimates vary markedly across ancestry groups within the same health-care system.
• Wider access to neurologic care, magnetic resonance imaging, and cell-based AQP4-IgG testing improves case ascertainment. Comparisons between countries should therefore account for differences in health-system access and diagnostic practice.

Low- and middle-income countries

• Reliable population-based estimates remain limited in many low- and middle-income countries. Restricted access to AQP4-IgG assays, magnetic resonance imaging, and specialist neurology services may lead to underdiagnosis and incomplete case ascertainment.
• In a 2026 multi-source study from southeastern Brazil, the crude prevalence was 3.07 per 100,000 persons; capture-recapture estimates ranged from 3.53 to 5.60 per 100,000 persons, illustrating how incomplete ascertainment can lower crude estimates.

Interpretation of epidemiologic estimates

• Epidemiologic estimates should be interpreted according to the diagnostic criteria and antibody assays used. Studies conducted before the 2015 International Panel for Neuromyelitis Optica Diagnosis (IPND) criteria may not be directly comparable with contemporary studies.
• Contemporary studies should report AQP4-IgG serostatus, use validated cell-based assays, apply the stricter criteria for AQP4-IgG-negative NMOSD, and exclude patients who fulfill diagnostic criteria for MOGAD.
• Changes in diagnostic criteria and greater access to testing can increase measured incidence or prevalence without proving a true rise in disease occurrence.