ACTRIMS 2026 | The incidence and prevalence of AQP4+ NMOSD: data from a universal health insurance system

New diagnostic criteria for NMOSD were announced in 2025, which really highlight the distinction of aquaporin-4 positive NMOSD. So previous studies that have evaluated NMOSD incidence and prevalence have often included aquaporin-4 positive, but also seronegative cases. So we were interested to evaluate incidence and prevalence restricted to aquaporin-4 positive NMOSD. We looked at this question in Canada where we have universal health insurance. So we were able to use central laboratory data to find all blood tests that were positive for the aquaporin-4 antibody. We then looked for people who had a demyelinating disease code, and the index date of NMOSD was determined by the date of the first demyelinating disease code in people who were also positive for the aquaporin-4 antibody. But we found a point prevalence as of 2024 of one per 100,000. And our mean incidence was 0.1 per 100,000 person years, although there was a little bit of fluctuation from year to year. So these numbers are similar to estimates in other global regions. We also looked for anybody who had a diagnostic code for nausea, vomiting, or hiccups in the five years preceding their first demyelinating diagnostic code, which could be suggestive of area postrema syndrome. So we found that 20% of our cohort actually had a code that was suggestive of area postrema, and these occurred a mean of one year before the first demyelinating disease code. We thought that this is also an important finding because it suggests that the proportion of people with area postrema syndrome at NMOSD onset may be somewhat higher than has been documented in the literature before.

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