2.1. Sarcoidosis

Sarcoidosis is a granulomatous inflammation of unknown origin involving various organs, most often the lungs and lymph nodes (Stirling et al. 1998). The prevalence of sarcoidosis is highly variable, ranging from 0.2/100000 in South America to 64/100000 in Sweden (Bauer & Löfgren 1964). The crude prevalence of sarcoidosis is 28.2 per 100000 and its annual incidence 11.4 per 100000 with a female predominance in Finland (Pietinalho et al. 1995). Sarcoidosis can present in an acute or subacute form, being mostly self-limiting, and the majority of patients recover spontaneously (Stirling et al.1998). However, 10-20% of sarcoidosis patients are at risk for developing progressive pulmonary fibrosis as a severe and irreversible complication, which may lead to permanent disability of the patient (Selroos 1969, Crystal et al. 1984). These patients require prolonged treatment with corticosteroids and occasionally cytotoxic therapy. Several markers of disease activity have been suggested. The serum level of angiotensin-converting enzyme (S-ACE) is a widely used indicator of sarcoidosis activity (Sharma 1986), although it does not reflect the activity of fibrogenesis (Harf et al. 1988). Serum interleukin-2 receptor (S-IL-2R) has also been shown to be elevated in sarcoidosis as well as in other lung diseases (Lawrence et al. 1988, Tsutsumi et al. 1994). Other suggested markers include ⁶⁷Ga-scan, computed tomography (CT) and HRCT as well as BALF cell subpopulations. An elevated T-helper/T-suppressor (CD4/CD8)-lymphocyte ratio in BALF has been suggested to be typical of sarcoidosis, although it has been recently shown to have low sensitivity for sarcoidosis (Kantrow et al. 1998). The results on these various markers have been inconclusive. The World Association for Sarcoidosis and Other Granulomatous Disorders (WASOG) meeting report concluded that the only routine tests to stage the ­activity of sarcoidosis are clinical investigation, chest radiography and lung function testing (Costabel et al. 1994).