To determine cumulative incidence and point prevalence of neuromyelitis optica spectrum disorder (NMOSD), multiple sclerosis (MS), and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) in Thailand using population-based data of Chumphon province.

CNS inflammatory demyelinating diseases (CNSIDDs) have a great interracial heterogeneity. The epidemiology of CNSIDDs in Thailand, a Mainland Southeast Asian country, is unknown.

Searching for CNSIDD patients at a public secondary care hospital in Chumphon from January 2016 to December 2021 was performed using relevant ICD-10-CM codes. All neurology patients were systematically referred to this hospital as it was the only hospital in the province with a neurologist. Diagnoses were individually ascertained by retrospective chart review. Cumulative incidence over 2016-2021, point prevalence on December 31st, 2021, attack rate, mortality rate, and disability-adjusted life years (DALYs) were calculated. Population data were obtained from the National Statistical Office of Thailand. As of December 31st, 2021, the population census of Chumphon was 509,479.

NMOSD was the most prevalent CNSIDD in adult Thai population at 3.33 per 100,000 persons (crude prevalence 2.55). The age-adjusted prevalence of aquaporin-4 antibody-positive NMOSD alone was 3.08 per 100,000 persons. Age-adjusted incidence rate of NMOSD was 1.65 per 100,000 persons/year (crude incidence rate 0.20). Age-adjusted prevalence of MS followed at 0.77 and MOGAD at 0.51 per 100,000 persons (crude prevalence 0.59 and 0.39, respectively). Although most had a fair recovery, disability was worst among NMOSD with a DALY of 3.47 years per 100,000 persons. Mortality and attack rates were highest in NMOSD as well. No increase in incidence or attack rate were observed during the COVID-19 pandemic.

CNSIDDs are rare diseases in Thailand. The prevalence is comparable to that of East Asian countries. NMOSD caused the highest DALYs among CNSIDDs.