Sex ratio of multiple sclerosis in the National Swedish MS Register (SMSreg)

BACKGROUND: Sex ratio in multiple sclerosis has been reported from several geographical areas. The disease is more common in women. In Europe the female-to-male ratio varies from 1.1 to 3.4. A recent study from Canada has reported a significant increase, with time, in female-to-male ratio in multiple sclerosis over the last 100 years. OBJECTIVE: The aim of this study was to analyse any change in sex ratio in multiple sclerosis in the Swedish population. METHODS: Data from the Swedish MS Register and data from the Swedish National Statistics Office were used to estimate sex ratio by year of birth and year of onset. RESULTS: In the analysis of sex ratio by year of birth there were 8834 patients (6271 women and 2563 men) born between 1931 and 1985. The mean women-to-men ratio was 2.62. No clear trend was noted for the women-to-men ratio by year of birth (Spearman's rho = 0.345, p = 0.298, n = 11). The number of patients analysed by year of onset was 9098 during the time period 1946 until 2005. The mean women-to-men ratio was 2.57. No significant change in women-to-men ratio (Spearman's rho = -0.007, p = 0.983, n = 12) with time was observed. CONCLUSION: There is no evidence for an increasing women-to-men ratio with time amongst Swedish multiple sclerosis patients.