Mortality trends in systemic sclerosis in France and USA, 1980-1998: an age-period-cohort analysis

We compared trends of Systemic Sclerosis (SS) mortality in France and the USA over the period 1980-1998 and used an Age-Period-Cohort (APC) model to adjust on the age at death of SS patients. All deaths coded with SS as an underlying primary or secondary cause in the national French and US mortality databases from 1980 to 1998 were included in the analysis. SS age-standardized mortality rates increased from 7.2 to 10.3/million in US women (+43%), and from 3 to 3.9/million in French women (+22%). Most of the increase occurred in senior women. In contrast, SS age-standardized death rates remained stable among US men (around 3/million) and French men (around 2/million). In US women, the APC analysis shows a growing cohort effect between 1900 and 1940, tending to stabilize for following cohorts. Similar findings were obtained to a lesser extent in French women. In conclusion, SS mortality rates increased by more than 40% between 1980 and 1998 in the USA, mostly in women born between 1900 and 1940. Whether these trends reflect rising incidence of SS need to be documented. The observed dissimilarity between genders and countries underline that environmental exposure and gender-related factors likely play a major etiological role. Stabilization in the following birth cohorts suggests that the increase of mortality observed since 1980 may slow down in the near future.