Sarcoidosis is a condition in which inflammatory cells produce nodules called granulomas in multiple organs. Granulomas can develop anywhere in the body, but they commonly affect the lungs, skin, lymph nodes, and eyes. Granulomas change the structure of the tissues around them and, in sufficient numbers they can cause damage, inflammation and symptoms and may interfere with normal functions.
The cause of sarcoidosis is not known. The condition is thought to be associated with both a genetic predisposition and the immune system's reaction to an environmental trigger – such as exposure to a virus, bacteria, allergen, dust, or chemical. . The incidence of sarcoidosis appears to be higher in Scandinavian countries and in Afro-Caribbean people, and also marginally higher in women. In general, incidence peaks between the ages of 20 and 50 years, with a second smaller peak after the age of 60. . In the UK, the incidence of the condition is estimated to be about 3/100,000 person-years based on general practice data. Sarcoidosis varies in severity. A person may have the disease without knowing it as mild cases cause no, few, or nonspecific symptoms. It can cause acute illness, resolve on its own within a few years (remission), recur, or continue as a chronic condition involving several organs causing severe symptoms and functional impairment. More than half of those affected will go into remission within 3 years of diagnosis, and two-thirds will be in remission within 10 years.
Most people with sarcoidosis will not experience long-term health effects, but about one-third will have some degree of organ damage. Sarcoidosis can cause blindness in rare cases and can sometimes be fatal, primarily in those with severe lung or heart involvement. The lungs are involved in most cases and are affected without other organ disease in approximately 50% of patients; the skin, liver and eyes are the most frequent extrapulmonary sites. There are significant differences in severity of disease and organ involvement depending on the ethnicity of the patient.