The incidence of SSc is reported to be 2-20/million population and the prevalence 4-290/million population. Based on distinct clinical aspects and courses of the disease an internationally accepted classification was established with two forms: limited cutaneous SSc (lSSc) and diffuse cutaneous SSc (dSSc). The disease is much commoner in females than males for reasons that are not entirely clear with a female-to-male ratio of 3-9:1. There are some populations at high risk as e.g. the Choctaw Indians from Oklahoma suggesting that genetic factors are critical. However, twin studies are inconclusive and familial aggregation is rare.
Both forms, however, lead to life threatening involvement of internal organs and large areas of the skin and are associated with marked excess mortality. The quality of life is severely reduced and the patients require continous medical support. Institution of regular physical therapy as early as possible to prevent loss of function is mandatory. Patient support groups play an important role in helping these patients to cope with their difficult psychosocial situation. The two major clinical variants are distinguished primarily on the degree and extent of skin involvement. The term overlap syndrome is used when features commonly encountered in other connective tissue diseases are present such as polymyositis or systemic lupus erythematosus.
The hallmark of SSc is fibrosis of the skin resulting early on in oedema, often the first indication of SSc skin involvement, which is followed by fibrotic induration and finally atrophy. Several skin scoring methodologies have been developed with the modified Rodnan skin score having the broadest distribution (Kahaleh et al, 1986; Furst et al. 1998). It is assessed by palpation of skin using a 0-3 scale (normal, mild, moderate or severe thickening) at seventeen areas. Following the skin score and the distribution of cutaneous induration is of major clinical importance, as patients with diffuse cutaneous scleroderma are much more likely to have significant heart and/or renal disease than those with the limited form of SSc, furthermore early disability and premature mortality are observed in this group (Clements et al. 1990). The period when skin thickening is most rapidly is also a time in which decline in visceral function is most likely to occur (Seibold 1994) (Fig. 1).
Diffuse Cutaneous SSc (dSSc)
dSSc is characterized by distal and proximal extremity and truncal skin thickening. Usually the elbows and knees are considered the dividing line. Leading symptoms of dSSC are: 1) onset of Raynaud's syndrome within 1 year of onset of skin changes (puffy or hidebound); 2) presence of tendon friction rubs; 3) early and significant incidence of interstitial lung disease, oliguric renal failure, diffuse gastrointestinal disease, and myocardial involvement; 4) absence of anti CENP-B antibodies; 5) nailfold capillary dilatation and capillary destruction; 6) anti-DNA-topoisomerase I antibodies (30%).
Limited Cutaneous SSc (lSSc)
Leading symptoms of lSSc are the following: 1) Raynaud's syndrome for years (occasionally decades); 2) skin involvement limited to hands, face, and forearms (acral) or absent; 3) a significant late incidence of pulmonary hypertension, with or without interstitial lung disease; 4) a high incidence of anti centromer (CENP-B) antibodies (70-80%); 5) dilated nailfold capillary loops, usually without capillary dropout; 6) skin calcifications and teleangiectasia particularly affecting the face and hands; 7) occasional late development of small bowel mal absorption.
A recent study suggests that systemic sclerosis sine scleroderma is a subset of SSc which should be included into the spectrum of SSc with limited cutaneous involvement and should not be considered as a distinct disorder (Poormoghim et al. 2000). Except for the absence of skin thickening, the group of patients with systemic sclerosis sine scleroderma had no significant differences in individual internal organ involvements, laboratory features, serum autoantibody type (e.g. anti-centromer) or survival rate compared with patients with lSSc. There was a tendency but no significant difference toward more pronounced pulmonary arterial hypertension and reduced carbon monoxide diffusing capacity (< 70% of predicted).
The most common overlap syndromes are Mixed Connective Tissues Disease (MCTD), Scleromyositis (PM-Scl-associated) and the Synthetase Syndrome (Jo 1-associated). MCTD and the Synthetase Syndrome are more extensively dealt with in chapter 7.
Scleromyositis is a scleroderma/polymyositis or scleroderma/dermatomyo-sitis overlap disorder associated with antibodies directed to the nucleolar PM-Scl complex and associated with HLA-DR3 (Genth et al. 1990). In a recent study of 108 cases, 83% of patients had characteristic manifestations (Jablonska and Blasczyk 1999). These findings include Raynaud's syndrome, scleroderma-like and dermatomyositis-like cutaneous changes of the face and hands including hyperkeratotic changes on the fingers, myalgia and arthritis. Pulmonary involvement occurs in about 30 to 60% of the patients (Mar-guerie et al. 1992). This syndrome is also a rather common subtype in children as about one third of the reported cases in the study of Jablonska (1999) are children with a mean age of onset at nine years. The course of this overlap syndrome is rather benign and usually responds to small or moderate doses of corticosteroids.
A broad variety of environmental factors have been reported to induce scleroderma (reviewed in Straniero et al. 1989). However, with few exceptions (contaminated tryptophan, contaminated rape seed oil, vinyl chloride, trichlorethylene) these cases are likely to represent random occurences. These scleroderma-like disorders often lack several features of SSc, in particular the autoimmune phenomena (autoantibody synthesis). In this respect, there has been much concern and publicity on the role of silicone (e.g. in the form of surgical implants) as a possible environmental factor for connective tissue diseases such as SSc, but despite several epidemiological studies, no link has been established (Janowsky et al. 2000).
In contrast, several studies indicate that silica dust-associated scleroderma can not be distinguished from SSc in terms of antibody profile and pheno-type (Haustein and Anderegg 1998). This is supported by experimental data suggesting that silica dust induces pathophysiological events similar to SSc (Haustein and Anderegg 1998).
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