Sarcoidosis is a relatively common disease of unknown etiology. Prevalence rates vary geographically, with higher rates in temperate climates. Differences in prevalence among races have also been noted with approximately a ten-fold higher rate in African-Americans than whites in the United States. Most frequently beginning in the third and fourth decades of life, the disease may occur in childhood or late in life. Presenting symptoms are frequently nonspecific and onset is usually insidious. Thoracic manifestations consisting of hilar adenopathy or pulmonary parenchymal involvement are most common and account for much of the morbidity associated with the disease. However, virtually every organ system may be affected, although involvement is frequently asymptomatic, and multiple organ involvement is common.

No infectious or inflammatory agent has been consistently identified as responsible for the development of sarcoidosis, although the immune system is no doubt involved. On biopsy, the diagnosis is suggested by the presence of typical noncaseating granulomas consisting of multinucleated giant cells surrounded by epithelioid cells and scattered lymphocytes. Varying degrees of fibrosis and hyalinization may be present. However, the finding of noncaseating granulomas is nonspecific and included in the differential diagnosis are Crohn's disease and other inflammatory or infectious agents. For this reason, cultures and special stains are necessary before a definitive diagnosis of sarcoidosis can be made histologically. More often, the diagnosis is suggested clinically by the typical presentation of asymptomatic bilateral symmetric hilar adenopathy on chest radiograph, particularly when associated with uveitis or erythema nodosum. The Kveim-Siltzbach test, which involves the intradermal administration of a preparation of sarcoid tissue, is not commonly performed in this country. An in vitro test for routine clinical purposes does not currently exist. Ultimately, diagnosis is based on a combination of clinical, radiological, and histologic features and, importantly, exclusion of other infectious or inflammatory entities.

Extrathoracic manifestations of sarcoidosis are not unusual and most commonly involve the skin and eyes. However, extrathoracic involvement without intrathoracic involvement probably occurs in less than 10% of patients. Intraabdominal manifestations of sarcoidosis are significantly less common than involvement of the eye, skin, heart, or musculoskeletal system. The most commonly involved abdominal organs include the liver, spleen, and lymph nodes. Hepatic and splenic involvement can have the appearance on computed tomography of hepatosplenomegaly or discrete parenchymal nodules. The presence of adenopathy seems to correlate with liver and spleen enlargement. Documented pancreatic involvement is very rare but can mimic carcinoma, presenting as abdominal pain and a pancreatic mass. Because of the prevalence of intrathoracic disease in patients with sarcoidosis, staging is based on the chest radiographic findings, and the presence of intraabdominal disease does not alter the staging.

The clinical course of patients with sarcoidosis is difficult to predict, with remission, either spontaneous or steroid-induced, possible. Sarcoid granulomas may ultimately resolve or undergo fibrosis. Fortunately, disease progression leading to death is uncommon (approximately 5%). Pulmonary fibrosis implies a poor prognosis. While other immunosuppressive agents have been evaluated for the treatment of sarcoidosis, corticosteroids remain the primary therapy when indicated.