Epidemiology of systemic sclerosis.

Systemic sclerosis is a family of disorders most appropriately considered in the category of the connective tissue diseases. Two major forms are recognized (diffuse cutaneous and limited cutaneous involvement subtypes), each with distinctive clinical and serologic findings as well as natural history. Scleroderma is characterized epidemiologically by several distinctive features. From a demographic viewpoint, the disease spares children and its incidence increases steadily with age among adults. If occurs much more frequently in women, especially during the child-bearing years, and most often and most severely in young black women, though there is no overall prominent racial predilection. The annual incidence approaches 20 per million population, and may be considerably underestimated. Both incidence and mortality have increased during the past several decades, but these changes are most likely a result of improved case detection rather than a true increase in incidence. Prevalence studies have not been undertaken, but 500 per million population may be a reasonable estimate. Family and genetic studies suggest a weak genetic predisposition, but several strong HLA associations with scleroderma-specific serum autoantibodies are evident. Certain environmental agents may be implicated in pathogenesis of scleroderma and closely related systemic illnesses associated with cutaneous fibrosis. The widespread pathologic process in systemic sclerosis leads to vascular insufficiency and fibrosis, which diminishes the reserve function of many organ systems. The result is considerable disability, especially affecting hand function, and a significant reduction in life span, with an overall 10-year survival from first physician diagnosis of under 70%. Further epidemiologic studies should take full advantage of established and newly proposed subsets of patients with homogeneous clinical, laboratory, serologic, and natural history features. The environment-host interactions noted here must be fully explored, especially in early untreated disease, where primary rather than secondary mechanisms are most likely to be operative.