Regional variation in the incidence rate and sex ratio of multiple sclerosis in Scotland 2010-2017: findings from the Scottish Multiple Sclerosis Register.

BACKGROUND: Fifteen regional studies published over the last six decades surveying prevalence, mortality and hospital admissions have suggested that Scotland is amongst the highest risk nations for multiple sclerosis (MS) in the world. However, substantial intranational variation in rates (between regions) has been described in numerous countries, including in the only previous Scottish national survey, which used hospital admission data, to address this issue. Against this backdrop, the Scottish Multiple Sclerosis Register (SMSR) was established in 2010 to prospectively collect nationally comprehensive incidence data and to allow for regional comparisons. METHODS: Here, we present the SMSR and analyse the variation in crude and age-sex standardized incidence rates, lifetime risk (cumulative incidence), and the sex distribution of cases and rates, between the 14 administrative Health Boards or regions of Scotland: 01 January 2010 to 31 December 2017. RESULTS: The overall incidence rate for Scotland was 8.76/100,000 person-years (standardized: 8.54). Regional incidence rates varied significantly-up to threefold-between Health Boards (p < 1 × 10-13). The national female-to-male sex ratio was 2.3:1, but this too varied regionally (outlier regions result in a range from 1.0 to 4.2:1). Lifetime risk ranged from 19.9/1000 for females in Orkney (58.98°N) to 1.6/1000 for males in the Borders (55.60°N). Comparison with a previous national survey suggests that these differences are longstanding. In 6 of 14 regions the lifetime risk for women exceeds 1%. CONCLUSIONS: This study introduces a national incidence register: a valuable research tool and the result of substantial public investment. The wide variation in incidence rates and sex ratios between regions, in a relatively homogenous population, raises questions for future study.

Latitudinal variation in MS incidence in Scotland.

AIMS: To explore the effect of latitude on incidence of multiple sclerosis (MS) in Scotland. METHODS: MS case data (2010-2015) was ascertained from the Scottish Multiple Sclerosis Register. Patient's postcode at diagnosis was linked to the Scottish Index of Multiple Deprivation (SIMD). Geographical data from SIMD was converted into latitude and longitude and patients were grouped by latitude band. A linear regression analysis was then performed. MS Cumulative Incidence was compared to population density calculated from SIMD. RESULTS: Latitude was associated with MS Incidence rate. Using a linear regression analysis (r2 = 0.22, p = 0.03), the data predicted an increase in the average MS Incidence of 1.31 cases/100,000 person years per increase in degree latitude. MS Cumulative Incidence rates rise with increasing northern latitude up until 59° north. CONCLUSIONS: We found an increasing incidence of MS with latitude without any relationship to population in Scotland. The reasons for this are likely to be multifactorial.