BACKGROUND: Particulate matter (PM) 2.5 (PM2.5) and PM10 are implicated in neurological diseases, yet their impact on central demyelinating diseases like multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) remains unclear. This study aimed to determine the association between the levels of PM2.5 and PM10 and the exacerbation of MS and NMOSD. METHODS: Patients with clinical exacerbations of MS and NMOSD in the Northern Thailand Registry from 2013 to 2022 were enrolled. Eligible patients were categorized based on air pollution exposure (defined as PM2.5 >
15 μg/m RESULTS: We analyzed 126 exacerbations in the PM2.5 database (mean age: 44.9±14.9 years, 114 NMOSD, 49 first exacerbations) and 135 exacerbations with the PM10 database (mean age: 44.9±14.9 years, 121 NMOSD, 54 first exacerbations), with the highest incidence four months post-peak air pollution. The PM2.5 exposure group had higher severity, showing increased rates of unfavorable EDSS at exacerbation and 90 days (56.3% vs. 23.6%, P <
0.001 and 47.9% vs. 16.4%, P <
0.001, respectively). Gadolinium enhancement in PM2.5 exposure was significantly higher (56.3% vs. 36.4%, P = 0.03). The PM2.5 exposure group also had a higher rate of second-line therapy with plasma exchange (21.1% vs. 7.3%, P = 0.03). PM2.5 exposure, not PM10, was associated with unfavorable EDSS at any time point, active radiological activity, risk of plasma exchange, and prolonged hospitalization. CONCLUSION: Environmental pollution, especially PM2.5, significantly impacts MS and NMOSD patients, influencing disease severity, causing permanent disability, and prolonging hospitalization. A national policy on pollution control is imperative, and further data on long-term exposure, together with other pollutants, is still required.