Despite changing trends among various subpopulations, the rate of mortality attributable to systemic sclerosis (SSc) vs non-SSc has remained high over 48 years, according to study data published in Arthritis Care & Research.
In a study of data from a 48-year period, researchers aimed to identify trends in mortality rates associated with SSc. Using the Centers for Disease Control and Prevention (CDC)’s database, they collected data on SSc deaths from 1968 through 2015, including those data where SSc was an underlying cause and where the disease was listed as a contributing cause. Death counts for the entire population for each year were also obtained, as well as separately by sex and race. The data were used to calculate the overall age-standardized mortality rate (ASMR) for SSc and non-SSc for each year, and sex and race as well. Based on this analysis, the ratio of SSc-ASMR to non-SSc-ASMR was calculated for each year. Trends in the data were assessed using a joinpoint regression model.
From 1968 through 2015, there were 46,798 deaths with SSc as the underlying cause and 106,058,893 deaths not related to SSc. The SSc vs non-SSc death rates were higher among women and Black persons. From 1968 to the early 2000s, SSc-ASMR increased at a higher rate for women than men (1.1%-2.9% vs 0.3%, respectively). The SSc-ASMR for women was also higher than for men (3.5 [95% CI 3.1-3.9] vs 1.8 [95% CI 1.5-2.1], respectively). At the beginning of the 48-year study in 1968, SSc-ASMRs for Black persons was 4.9 (95% CI, 3.8-6.1) that was higher than for White persons at 2.4 (95% CI, 2.2-2.6), after which there was a higher annual increase in SSc-ASMR for White persons. Over the 48 years, SSc-ASMRs increased by 33.3% for White persons and decreased by 20.4% for Black persons.
Overall, SSc-ASMR increased between 1968 and 1987 at an annual percent change of 1.0%; from 1987 to 2001, the increase was at an annual percent change of 2.2%. From 2001 through 2015, there was a steady decrease in SSc-ASMR, with non-SSc-ASMRs either decreasing or remaining stable throughout the study period. In 2015, the SSc-ASMR was still greater than in 1968, compared with mortality rates in the general population.
Through their analysis, the researchers revealed that despite a 15-year decrease, mortality rates for SSc-related deaths did not match the improvement in non-SSc-related mortality rates among the general population. They indicated that the increase in SSc-ASMR from the 1960s through the 1990s could be because of increased disease diagnosis. In addition, some treatments in use during those decades could have inadvertently contributed to mortality rates. With regard to higher SSc-ASMR for women than men, the researchers noted that SSc may have been recognized and recorded more often in women, though this did not necessarily point to differences in disease severity between men and women. Despite this, the findings indicated that SSc mortality burden was greater among women than men.
Study limitations included dependence on the accuracy of coding on death certificates, the possibility of SSc-related deaths being listed under an unrelated cause, such as infection or cardiovascular disease, could be related to SSc, and the possible under-reporting of SSc deaths in certain subpopulations.
Researchers concluded, “…SSc mortality has begun to improve after the year 2000. Still, the improvement in SSc mortality has not kept up with an improvement in mortality from other causes in the general population. Comprehensive examination using prospective, population-based data could help clarify the mechanisms of the changing disparities in SSc mortality and identify modifiable risk factors that could be altered to improve outcomes.”
Yen EY, Singh DR, Singh RR. 48‐year trends in systemic sclerosis mortality, 1968‐2015: A United States population‐based study. Published online August 8, 2020. Arthritis Care Res. doi:10.1002/acr.24411