The age at onset of relapsing-remitting multiple sclerosis has increased over the last five decades

Background: Patients with relapsing-remitting multiple sclerosis (RRMS) most commonly experience their first symptoms between 20 and 40 years of age. The objective of this study was to investigate how the age at which the first symptoms of RRMS occur has changed over the past decades. Methods: Patients who were followed up in our unit after an initial diagnosis of RRMS using the Poser or McDonald criteria and who experienced their first symptoms between January 1970 and December 2019 were included in the study. The cohort was divided into five groups according to the decade in which the first symptoms appeared. The age at disease onset was compared across decades. Changes in age were also deter-mined after excluding patients with early-onset disease (< 18 years of age) and those with late-onset disease (> 50 years of age) to avoid bias. Results: The cohort included 1,622 patients with RRMS, 67.6% of whom were women. Among them, 5.9% and 4% had early-onset and late-onset disease, respectively. The mean age +/- standard deviation at onset was 31.11 +/- 9.82 years, with no differences between men and women. The mean ages at onset were 23.79 +/- 10.19 years between 1970 and 1979, 27.86 +/- 9.22 years between 1980 and 1989, 30.07 +/- 9.32 years between 1990 and 1999, 32.12 +/- 9.47 between 2000 and 2009, and 34.28 +/- 9.83 years between 2010 and 2019. The ages at disease onset were progressively higher in the later decades; this trend was statistically significant (p < 0.001), with a Pearson linear correlation coefficient R of 0.264 and R2 of 0.070 (p < 0.001). The results were similar when analysing men and women separately. We conducted an analysis of 1,460 patients (mean age at onset: 31.10 +/- 7.99 years), after excluding patients with early-onset and late-onset disease. In this specific subgroup, the mean ages at disease onset were 28.38 +/- 8.17 years between 1970 and 1979, 29.22 +/- 7.51 years between 1980 and 1989, 30.06 +/- 8.02 years between 1990 and 1999, 31.46 +/- 7.77 years between 2000 and 2009, and 33.37 +/- 7.97 years between 2010 and 2019. The trend was also statistically significant (p < 0.001), with a Pearson linear correlation coefficient R of 0.193 and R2 of 0.037 (p < 0.001). Conclusion: Our data showed that the age at RRMS onset has increased over the past decades.