The increased female:male mortality ratio in multiple sclerosis (MS)-associated mortality is driven mainly by increased mortality among females in the 3 last decades, according to a recent study, particularly in the older age groups. It is best explained by disproportional period effects, providing evidence of time-varying external factors, including improved access to diagnosis among females. Researchers collected MS mortality data from 1951 to 2015 from a national registry. Age-period-cohort analysis was conducted using log-linear Poisson models, including sex interaction terms. They found:
- MS was registered as the underlying, contributing or direct cause in 6,060 deaths.
- MS-associated mortality remained stable with a slight preponderance among males until after 1980, and have since increased preferentially among females.
- Throughout the study period, the mean annual increase was 1.25% for females and 0.3% for males.
- The period effect evened out for males in the last 3 decades but increased for females, especially among the oldest age groups.
Nakken O, Lindstrøm JC, Holmøy T. Sex ratio in multiple sclerosis mortality over 65 years; an age-period-cohort analysis in Norway. [Published online ahead of print March 21, 2018]. J Neurol. doi:10.1007/s00415-018-8832-9.