Trends in incidence, mortality, and causes of death associated with systemic sclerosis in Denmark between 1995 and 2015: a nationwide cohort study

Background: To investigate the incidence and the mortality-rates of systemic sclerosis (SSc), its primary causes of death, and the temporal trends in events in Denmark during the last decades.

Methods: Using the Danish National Patient Registry, we identified all persons aged ≥18 years with a first-time diagnosis of SSc (ICD-10 code M34, excluding M34.2) between 1995 and 2015.

Results: A total of 2778 incident SSc cases were identified. The mean age at time of SSc diagnosis was 56 (standard deviation 15) years and 76% were women. The overall incidence rate (per 1,000,000 person-years) of diagnosed SSc was 24.4 (95% confidence interval 23.6-25.4), with a slight increase over the study period, age- and sex-adjusted incidence rate ratio 1.02 (95% confidence interval 1.01-1.02) per 1-year increase. The 1-year all-cause mortality rate per 100 person-years decreased from 6.1 (3.1-12.2) in 1995 to 5.3 (2.5-11.1) in 2015, sex- and age-adjusted hazard ratio 0.96 (95% CI 0.94-0.98) per 1-year increase. Over the period, the average age at SSc diagnosis increased and the proportion of women decreased, whereas the burden of comorbidities increased. One fifth of all deaths were attributable to cardiovascular causes, a fourth to pulmonary diseases, and 15% were due to cancer.

Conclusions: Within the last few decades, the incidence of SSc has increased and the 1-year mortality rate has decreased slightly in Denmark. Almost half of all deaths were attributable to cardiopulmonary causes.