Epidemiology of systemic sclerosis and related diseases.

Epidemiologic studies of scleroderma can provide insight into the dynamics of disease expression over time, over different geographic areas, and over diverse ethnic populations. Although such population studies cannot establish cause and effect relationships, they can reveal associations previously obscured by the relative rarity and clinical diversity of this disease. The incidence rate of systemic sclerosis has been stable over the past 20 years at 19 new cases per million per year. The incidence rate of localized scleroderma or morphea is reported at 27 new cases per million per year and has a benign prognosis overall. Disease expression of systemic scleroderma is influenced by genetic, ethnic, and environmental factors. A cluster of scleroderma cases among Choctaw Native Americans in Oklahoma provides an opportunity to investigate the interaction of genetic and environmental influences. Twin studies suggest a definite but relatively weak genetic component. Case-control studies regarding environmental and occupational exposures have yet to identify risk factors that could serve as triggers for this disease.