Estimates of incidence (number of new cases per year) and prevalence (total number of active cases) of systemic scleroderma vary widely depending on geographic location and classification criteria. However, recent studies (Mayes 2003) estimate that in the US the incidence of new cases is about 20 per million adults (about 4800 new cases per year based on current US population estimates) and that the current prevalence was about 240 cases per million adults (about 60,000 diagnosed cases). The American College of Rheumatology estimates that the number may be as high as 100,000 people in the US. Recent international studies suggest that systemic scleroderma occurs at about the same rates in the United States and most of Europe. Other places in the world appear to have somewhat lower rates. These regional differences may be a consequence of differential genetic susceptibility to scleroderma, different exposure to possible environmental triggers, different diagnostic criteria, or a combination of all of these factors.
Systemic scleroderma may occur at any age, but the symptoms most frequently begin in mid-life (25-45). The diffuse and limited forms of scleroderma are very rare in children. The disease is about 4 times more common in women than men for diffuse variants of scleroderma with a slightly higher female-male ration in the limited variants. There is some evidence that black women have a significantly greater risk than white women. In addition, diffuse scleroderma appears to occur more frequently among black women and starts at an earlier age. Native Americans of the Choctaw tribe have especially high rates of scleroderma.
There seems to be a relatively weak genetic link with scleroderma. Close order relatives of an affected individual are more likely to have some type of autoimmune condition but this is more likely to be a different disease such as rheumatoid arthritis, Hashimoto’s (autoimmune hypothyroidism), Graves (autoimmune hyperthyroidism), or lupus. Also, close order relatives of affected patients may have elevated ANA levels as compared to the normal population, but without any symptoms of any autoimmune disease.