What is sarcoidosis?

Causes and Symptoms

Sarcoidosis, an inflammatory disease of unknown cause, affects multiple organs and systems in the body. Most commonly affected are the lungs, lymph nodes, skin, and eyes. Other organs and systems that can be involved include the liver, spleen, bone, joints, heart, muscle, and central nervous system. Sarcoidosis is thought to be the result of an unusual immune reaction to an environmental antigen, such as a bacterium, fungus, or environmental toxin. Sarcoidosis is characterized by the presence of noncaseating granulomas in the affected tissues. These granulomas are ball-shaped clusters of immune cells consisting of macrophage and epitheloid cells encircled by lymphocytes. A granuloma begins when certain types of lymphocytes interact with antigen-presenting cells. Macrophages that have engulfed antigens are chronically stimulated by cytokines, differentiate into epitheliod cells, and fuse to form multinucleated giant cells. If a granuloma persists for an extended period of time, then fibroblasts and collagen encase the ball of cells. This eventually leads to
fibrosis, or permanent scarring, which can lead to organ impairment.

The incidence of sarcoidosis varies greatly by ethnic group, indicating a genetic component to sarcoidosis. In the United States, forty in one hundred thousand African Americans develop sarcoidosis, while five in one hundred thousand Caucasians develop it. In Sweden, the incidence is sixty-four in one hundred thousand. In general, more women develop sarcoidois than do men. Sarcoidosis can occur at any age, but the average age when it is detected is between twenty and forty years.

The initial symptoms of sarcoidosis may include coughs, wheezing, chest discomfort, night chills, and weight loss. Many patients learn that they have sarcoidosis when a routine chest X ray shows abnormalities. Most if not all of the symptoms of sarcoidosis are not unique to the disease, so diagnosis involves ruling out other conditions, such as an infection. Typical first signs of sarcoidosis include skin lesions, problems with the lungs (such as decreased lung function), and enlarged lymph nodes. A bronchoscopy may be performed to inspect the bronchial tubes and to obtain a tissue for biopsy. A positive biopsy would reveal a large number of white blood cells, general inflammation, and the presence of granulomas. Gallium-67 scans may be used, in which the radioactive element gallium-67 is injected and accumulates in areas of inflammation, infection, or rapid cell division. More recently, the more sensitive FDG-PET scan, which uses the radioactive sugar FDG instead of gallium, is being used for some patients. Patients with sarcoidosis in the eyes have redness in the eyes, photophobia, and blurred vision.

Treatment and Therapy

An estimated 60 to 70 percent of cases of sarcoidosis will resolve within one to two years. For severe sarcoidosis, corticosteroids, such as prednisone, are given to reduce inflammation. Since steroids can have severe side effects, treatment may not be given unless organs are impaired. Some 20 to 30 percent of patients will develop a chronic condition of persistent sarcoidosis that damages organs as a result of fibrosis. It is estimated that in 5 to 10 percent of patients, sarcoidosis will be the cause of death, usually from lung fibrosis resulting in respiratory failure or from cardiac or neurological complications.

Perspective and Prospects

The skin lesions of sarcoidosis were first recognized in 1869 by English dermatologist Jonathan Hutchinson. In 1897, Caesar Boeck independently described the skin lesions using the term “sarcoidosis,” meaning “fleshlike condition.” The multiple system involvement was recognized by Jörgen Schaumann in 1915, the same time that Alexander Bittorf described lung lesions of the condition. In 1941, Morten A. Kveim, a Norwegian physician, developed a test for sarcoidosis that involved injecting lymph node tissue from a confirmed sarcoidois patient into the skin of a person suspected of having sarcoidosis. If granulomas developed at the injection site four to six weeks later, then the test was positive for sarcoidosis. In 1954, Louis Siltzbach modified the test to inject tissue from the spleen of sarcoidosis patients. If the patient was receiving steroid treatment, then the granulomas might not develop, leading to a false negative on the test. The Kveim test is no longer used to diagnose sarcoidosis, largely because of the lack of commercially available Kveim reagent and its replacement by other
diagnostic methods, such as bronchoscopy. A promising new development in the treatment of extensive sarcoidosis is the use of FDG-PET to monitor a patient’s response to drug therapy. FDG-PET is more sensitive than the conventional gallium method. Research into the genetics of sarcoidosis indicates likely multiple genetic factors. A predisposition to developing sarcoidosis is associated with HLA-DQ and HLA-DR genes.

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"What Is Sarcoidosis?" National Heart, Lung, and Blood Institute, May 1, 2011.

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