Multiple sclerosis incidence: A systematic review of change over time by geographical region

• Published in: Multiple sclerosis and related disorders 2022-07, Vol.63, p.103932-103932, Article 103932
• Main Authors: Lane, Jo, Ng, Huah Shin, Poyser, Carmel, Lucas, Robyn M, Tremlett, Helen
• Format: Article
• Language: English
• Subjects: Epidemiology; Incidence; Multiple sclerosis; Systematic review
• ISSN: 2211-0348; 2211-0356
• DOI: 10.1016/j.msard.2022.103932

•Trends in MS incidence rates over time have not been examined on a global basis.•Our systematic review included 65 regional estimates across 24 countries.•By absolute number of studies, the predominant pattern was increasing MS incidence.•No pattern was seen with consistent case definitions/high population coverage.•There were few eligible studies to assess change in incidence in many regions. The incidence of multiple sclerosis (MS) has reportedly increased over time; however, change in MS incidence has not been rigorously assessed globally. We followed the guidelines for the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. Two independent reviewers systematically searched Scopus, PubMed and Web of Science for peer-reviewed publications in English from 1 January 1985 to 24 September 2020 reporting MS incidence for at least two contiguous five-year periods with clearly-defined case ascertainment. The outcome was change in MS incidence rate according to geographical region. We identified 64 papers providing 65 regional estimates (including three paediatric-onset MS) across 24 countries covering ∼3% of the world's population (in 2000/1 or closest available total population for the entire country), with quality (adapted Newcastle-Ottawa Scale) ranging from sufficient to good. Studies were mainly from Italy (n=14 including San Marino), Norway (n=10) or Canada (n=9), with no studies in the Africa or South-East Asia regions. Of the 62 whole-of-population estimates, MS incidence rates: significantly increased in 38 (61%), significantly decreased in 13 (21%) and remained stable in 11 (18%). In the paediatric-onset studies, MS incidence was stable in two (67%) and increased in one (33%). Many estimates derived from only selected (often small) regions of a country. For 42 (68%) of the whole-of-population estimates (and two of the paediatric-onset estimates) a consistent case definition or diagnostic criteria over the entire study period was explicitly reported. Across the n=9 whole-of-population estimates based on a consistent case definition for the duration of the study period, and including a substantial proportion of the population of a country (≥one-third), incidence rates were stable in n=3, increased in n=3 and decreased in n=3. Studies using a consistent case definition covered ∼2.7% of the global population; incidence rates were stable in 0.9% of the global population, decreased in studies covering 1%, and increased in