Temporal trends in the incidence and prevalence of multiple sclerosis among individuals from Khuzestan living in Isfahan: A population-based study from Iran (1977-2016)

Abstract

Background: The Khuzestan province has had a lower MS burden than the Isfahan province, Iran, despite comparable latitude, ultraviolet, and air pollution indices. Objective: To estimate the incidence and prevalence of MS in immigrants from Khuzestan arriving at Isfahan, as well as the death (mortality) rate among immigrants with MS, and to compare the clinical attributes of ones with MS, e.g., age at onset/diagnosis, clinical subtype (e.g., relapsing-remitting, primary/secondary progressive), and EDSS, with matched native-born people with MS (pwMS). Methods: Data consisting of demographics of the people from Khuzestan arriving in Isfahan was retrieved from national census reports. The MS registries of Isfahan University of Medical Sciences and the Isfahan MS clinic, were used to identify the immigrant MS cases, and the date of neurologist MS diagnosis from 1977 to 2016. The MS-related data were retrieved for the cases where available, from the Isfahan MS clinic registry. A 1:1 age, sex, and socioeconomic status-matched cohort of pwMS born and living in Isfahan were randomly selected from the Isfahan MS clinic database as comparison for MS-related clinical factors. Results: The MS incidence rate among immigrants consistently increased over the years, reaching 9.2 cases (95 CI 8.0, 10.4) per 100,000 person-years in 2007-2016. The prevalence of MS at the end of 2016 among the immigrants reached 160.9 (95 CI 150, 180) per 100,000 persons. The death rate among immigrants with MS was 30.7 (95 CI 16.3, 52.5) per 10,000 person-years in 2007-2016. Age-standardized and gender-specific figures followed similar trends with the crude figures. A higher proportion of immigrants who were younger upon arrival (especially ones <10 years old) were subsequently diagnosed with MS (compared to ones older upon arrival, Pearson Chi-square: 390.7, df: 6, p < 0.0001). The immigrants were younger at the time of MS diagnosis compared to matched controls (mean difference: 1.2 years; p = 0.05), but were of comparable age with them at the recalled time of MS onset (mean difference: 0.9 years; p = 0.16). Among relapsing-onset cases, Poisson regression (offset by duration since diagnosis) showed higher odds of secondary progressive conversion in immigrants versus controls (OR: 1.40; 95 CI: 1, 1.98; p = 0.05). The immigrants also had overall higher EDSS scores at the end of 2016 than the native-born controls (Mann-Whitney U: 58,249, p < 0.001). Comorbidities, smoking status, and family history of MS were similar between the two groups (all p values > 0.05). Conclusion: Immigrants' MS risk figures have been considerable. Their MS attributes were mostly similar with native-born pwMS. The reason(s) for these findings warrants further investigation.