From the perspective of epidemiology, the following questions are relevant to scleroderma pathogenesis: What is the pattern of disease occurrence? Have the rates of incidence and prevalence been stable over time? What populations are most affected? What are the risk factors for disease development, expression, and survival? Does the overall population incidence rate obscure subpopulations at higher risk? If so, what are the characteristics of these subpopulations? By identifying risk factors and analyzing the relative contributions of these factors, a model can be formed and hypotheses tested regarding the cause(s) of this disease.

This article will deal only with systemic sclerosis, in both its limited and diffuse forms. Localized forms of scleroderma (including morphea and linear scleroderma) will not be considered. The 1980 systemic sclerosis classification criteria<sup>50 Subcommittee for Scleroderma Criteria of the American Rheumatism Association Diagnostic and Therapeutic Criteria Committee Preliminary criteria for the classification of systemic sclerosis (scleroderma) Arthritis Rheum 1980 ;  23 : 581

Cliccare qui per andare alla sezione Riferimenti</sup> greatly facilitated epidemiologic studies by providing a common definition for this disease. Earlier studies<sup>11 Farmer R.G., Gifford R.W., Hines E.A. Prognostic significance of Raynaud's phenomenon and other clinical characteristics of systemic scleroderma Circulation 1960 ;  21 : 1088

Cliccare qui per andare alla sezione Riferimenti, 34 Medsger T.A., Masi A.T. Epidemiology of systemic sclerosis (scleroderma) Ann Intern Med 1971 ;  74 : 714

Cliccare qui per andare alla sezione Riferimenti, 35 Medsger T.A., Rodnan G.P., Robinson H. Survival with systemic sclerosis (scleroderma). A life-table analysis of clinical and demographic factors in 309 patients Ann Intern Med 1971 ;  75 : 369

Cliccare qui per andare alla sezione Riferimenti, 37 Michet C.J., McKenna C.H., Elveback L.R. , e al. Epidemiology of systemic lupus erythematosus and other connective tissue disease in Rochester, Minnesota, 1950 through 1979 Mayo Clin Proc 1985 ;  60 : 105

Cliccare qui per andare alla sezione Riferimenti</sup> did not have this benefit, making direct comparisons between pre- and post-1980 studies somewhat problematical. Additionally, it has been estimated that the 1980 classification schema will miss some 10% of individuals with limited disease.<sup>36 Medsger T.A. Comment on scleroderma criteria cooperative study Systemic Sclerosis (Scleroderma). New York: Gower (1985).  16

Cliccare qui per andare alla sezione Riferimenti</sup> Noting these limitations, analyses of studies that describe disease patterns over time and in different areas are still valuable in contributing to our understanding of scleroderma.