Sarcoidosis: the links between epidemiology and aetiology.

Sarcoidosis is a multisystem inflammatory disease, the aetiology of which has still to be resolved. The proposed mechanism is that a susceptible genotype is exposed to one or more potential antigens. A sustained inflammatory response follows, which ultimately results in pathognomonic granuloma formation. Various clinical phenotypes exist with specific genetic associations influencing disease susceptibility, protection, and clinical progression. Occupational and environmental factors, including microbial elements, may then effect the development of this disease. Sarcoidosis is a heterogeneous disease, showing geographic and racial variation in clinical presentation. It demonstrates a familial tendency and clear genotype associations. Additionally, it appears to cluster within closely associated populations (eg, work colleagues) and appears to be related to selected occupations and environmental exposures. Frequently occult, but occasionally fatal, this disease has a very variable prognosis. It is also unusual in having no specific biomarker. The epidemiology and multiple factors that appear to influence the aetiology of sarcoidosis illustrate why this disease state is frequently described as a clinical enigma. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.