Clinically distinct fibrosing processes affecting the skin, selected internal organs, or both in a characteristic pattern are a common cause of morbidity. In addition to systemic sclerosis, the prototype idiopathic fibrosing disorder, these conditions include the eosinophilia-myalgia syndrome, epidemic toxic oil syndrome, eosinophilic fasciitis, localized forms of scleroderma, keloid, and the newly described entity of fibrosing colonopathy. The pathogenesis of these disorders, although still incompletely understood, appears to share similarities with that of systemic sclerosis. Insights into these diseases have recently emerged from epidemiologic and toxicoepidemiologic investigations, in situ hybridization and polymerase chain reaction amplification of target genomes, and in vivo and in vitro experimental research. Minor contaminants in food supplements, activation and degranulation of eosinophils, altered expression of CD34 antigen on dendritic cells, disordered regulation of fibroblast apoptosis and proliferation, infection with Borrelia organisms, and cytokines such as transforming growth factor-β, interleukin-4, and connective tissue growth factor are implicated in inducing an accentuated and persistent fibrogenic host response to injury, resulting in tissue fibrosis. In addition, humoral and cellular autoimmunity may also be implicated.
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