Thirty-year trends in the prevalence and incidence of multiple sclerosis (MS) in Mazandaran Province: Application of advanced statistical methods.

Mazandaran province in Iran, identified as a high-prevalence area, has lacked comprehensive long-term studies on MS trends. This study aims to fill that gap by analyzing three decades of MS incidence and prevalence in Mazandaran using advanced statistical methods. This longitudinal study included clinically diagnosed MS cases from the two most populous cities in Mazandaran utilizing data from the national MS registry spanning 1994 to 2023. Prevalence and age-adjusted incidence rates were calculated, and annual percentage change (APC) was assessed using joint point regression. Bayesian statistical methods were applied for comprehensive trend analysis. A total of 1333 MS patients were identified, the mean (±sd) age at diagnosis was 28.58±8.52 years. MS prevalence increased from 0.19 per 100,000 in 1994 to 127.24 per 100,000 in 2023. The age-adjusted incidence rate rose from 0.14 (95 %CI: 0-0.5) in 1994 to a peak of 10.44 (95 %CI: 7.8-13.0) in 2018, then declined to 4.39 (95 %CI: 2.7-6.1) in 2023. The APC in MS incidence was +14.1 % until 2018, followed by a -15.32 % decrease thereafter. Significant differences in mean age, Expanded Disability Status Scale (EDSS) score and MS type were observed before and after 2018. The Bayesian methods indicated that evaluated predictors were not statistically significant for MS prevalence. This study demonstrates a marked increase in MS incidence in Mazandaran province until 2018, followed by a subsequent decline. The rising prevalence and decreasing mean age at diagnosis underscore the need for continued surveillance and further research to determine whether the recent decline in incidence will persist.