Geoepidemiology of systemic sclerosis

Systemic sclerosis (SSc) is a rare and potentially severe connective-tissue disease, characterized by skin fibrosis and involvement of internal organs. Because of its rarity and heterogeneous clinical presentation, reliable epidemiological studies on SSc have been particularly difficult to carry out. SSc prevalence is estimated between 3 and 24 per 100,000 population and appears to be higher in North America and Australia as compared to Europe and Japan. Incidence estimates have significantly increased between the fifties and the eighties, but this could result from greater physician awareness of the disease and more reliable ascertainment methods. Risk factors for SSc include female sex and African origin. Reports of sporadic clusters of higher prevalence also suggest environmental risk factors. In particular, silica and solvents exposure has been associated with SSc by several rigorous case-control studies. The ten-year cumulative survival of SSc has improved significantly from 50% in the seventies to over 70% at the present time. Pulmonary fibrosis and pulmonary arterial hypertension are now the two main causes of death. Diffuse cutaneous forms, as well as cardiac, pulmonary, and renal involvement are independent risk factors for SSc-related mortality.