Secular Trends in Systemic Sclerosis Mortality in the United States from 1981 to 2020

Background: Systemic sclerosis (SSc) has the highest mortality rate among autoimmune disorders. Individuals with SSc frequently die from complications or infections related to SSc. Nonetheless, the sex–age–period interaction of SSc is complex and remains unclear. The study aims to analyze the secular trend of SSc mortality based on data regarding underlying cause of death (UCD) and multiple causes of death (MCD) and clarify the sex–age interaction with time. Methods: The multiple-cause mortality statistics provided by the National Center for Health Statistics were used to identify all deaths in the United States from 1981 to 2020 in which SSc was indicated anywhere on the death certificates. The age-standardized mortality rate (ASMR) was determined for both sexes, as well as the variations in these rates. Joinpoint regression analysis was utilized to determine the annual percentage change (APC) of ASMR. Results: A total of 44,672 and 66,259 individuals who died between 1981 and 2020 were identified based on the UCD and MCD data, respectively. According to the UCD data, SSc-related AMSR (SSc-ASMR) of the male and female decedents, respectively, declined from 5.01 and 1.94 in 1981–1990 to 4.77 and 1.32 in 2011–2020, respectively (mortality rate ratio 0.95, 95% confidence interval 0.92–0.98). From 1986 to 1999, the APC of SSc-ASMR in female decedents decreased except for those aged 45–64 years (APC 2.1%, p = 0.002). For MCD analysis, in trend 1, only APC of SSc-ASMR in male decedents aged 45–64 years decreased. The SSc-ASMR of both male and female decedents fell on trend 2 arm. In 2011–2020, the ratio of UCD to MCD increased across all age groups for both sexes compared to 1981–1990. Overall, compared to the male decedents, the SSc-ASMR in female decedents increased significantly before 1999, peaked in 1999, followed by continuous decrease until 2020 according to UCD and MCD statistics. Conclusions: Over the past four decades, the SSc deaths based on the MCD data were 1.48 times more than the UCD data, and the proportion of UCD over MCD increased over time. The SSc-ASMRs in all the sex–age groups significantly decreased over the past two decades. Notably, the mortality rate ratio of women to men with SSc increased in the past four decades.