Epidemiology of aquaporin-4 seropositive neuromyelitis optica spectrum disorder in the Alicante health area, Spain: A population-based study.

BACKGROUND

Neuromyelitis optica spectrum disorder (NMOSD) is an uncommon antibody-mediated inflammatory disease. The prevalence and incidence of NMOSD vary widely between geographical areas and ethnicities. To date, the only epidemiological study on NMOSD conducted in Spain has estimated an incidence rate of 0.63 per 1,000,000 person-years and a prevalence rate of 0.89 per 100,000 individuals in the general population. This population-based study aimed to estimate the incidence and prevalence of aquaporin-4 (AQP4)-seropositive NMOSD in the Alicante Health Area, Southeastern Spain, according to the 2015 International Panel for NMO Diagnosis (IPND) criteria and to investigate potential clinical and epidemiological differences that may exist in Spain in relation to NMOSD.

METHODS

In this retrospective population-based study, all patients diagnosed with AQP4-seropositive NMOSD according to the 2015 IPND criteria were identified using multiple sources. Seropositivity for AQP4 was confirmed in all cases using a cell-based assay. Two neurologists assessed the compliance with the 2015 IPND criteria. Clinical, imaging and laboratory data were obtained from medical records. The prevalence and incidence of AQP4-seropositive NMOSD were calculated using the Population Information System (SIP) data from the Alicante Health Area. The incidence rate covers January 2013-January 2023. The 95 % confidence intervals (CI) were calculated for the prevalence and incidence rates using Epidat software. Age-adjusted rates were calculated by the direct method of standardisation using Eurostat's European Standard Population in 2013 (ESP 2013) and the World Health Organization's World Standard Population expected in 2000-2025 (WHO 2000-2025) as reference populations.

RESULTS

Nine AQP4-seropositive NMOSD patients were identified in the Alicante Health Area. All patients except for one were Caucasian. The female-to-male ratio was 8:1, and the median age at onset was 39 years (range: 21-77 years). Most common clinical presentation was optic neuritis (five patients), followed by longitudinally extensive transverse myelitis (three patients) and postrema area syndrome (one patient). At the time of the study, all patients were being treated with chronic immunosuppressant treatment: tocilizumab (5/9 patients) and rituximab (4/9 patients). The overall prevalence rate was 3.11 (95 % CI: 1.42-5.91) per 100,000 individuals, while the overall annual incidence rate was 1.78 (95 % CI: 0.58-4.15) per million individuals. The age-standardised prevalence rate (using ESP 2013) was 3.09 (95 % CI: 0.62-8.77) per 100,000 individuals, and the annual incidence rate was 1.74 (95 % CI: 0.70-3.61) per million individuals. In addition, the age-standardised prevalence rate to the WHO 2000-2025 was 2.56 (95 % CI: 0.81-5.83) per 100,000 individuals, and the annual incidence rate was 1.66 (95 % CI: 0.54-3.89) per million individuals.

CONCLUSION

The crude and age-standardised prevalence rates of AQP4-seropositive NMOSD in our study were higher than those reported in other European studies. Our findings underscore that the epidemiology of AQP4-seropositive NMOSD is not uniform across Europe.