Overview of Sarcoidosis
Sarcoidosis is a fairly common disease with an annual incidence rate of approximately 11 per 100,000 in Caucasians and approximately 36 per 100,000 African Americans in the United States. It is most common in young adults between the ages of 20 and 40. The word "sarcoidosis" comes from the Greek word "sarkodes," meaning "fleshy," and the Greek suffix "-osis," meaning "condition." The "fleshy condition" refers to the skin lesions that often form on various parts of the body.
Sarcoidosis is a multisystemic disease that can affect a variety of organs. Pulmonary (lung) involvement occurs in greater than 90 percent of patients and is a leading cause of morbidity and mortality from this disease. Many organs can be involved in sarcoidosis, in fact, one of the most noticeable symptoms is the peculiar skin lesions, erythema nodusum, that develop on the lower legs.
Sarcoidosis is a disease of unknown etiology characterized by granuloma formation in a variety of organs. Granulomas are collections of immune cells and disease that result from granulomatous disorders. There are a variety of granulomatous disorders that closely resemble sarcoidosis, including tuberculosis.
The close resemblance to tuberculosis has led to speculation that sarcoidosis is due to an infectious organism. It is the formation of granulomas and the resulting tissue damage caused by the cells within these granulomas that cause the symptoms of sarcoidosis. However, often these granulomas are not of significant number or in a critical location to cause symptoms.
The way in which sarcoidosis presents varies remarkably from case to case. In some patients, it is short-lived and mild, and in others it becomes a chronic, debilitating sickness.
Unfortunately, there is no "cure." Sarcoidosis usually is self-limiting, meaning that it resolves on its own or does not progress. Many cases do not require treatment. Sometimes, however, the condition progresses to fibrosisthe formation of scar-like fibrous tissuethat permanently impairs function of the affected organ.
Corticosteroids are the mainstay of therapy to treat sarcoidosis. They help suppress the inflammation and prevent granulomas and fibrosis from forming.
What is a granuloma?
Sarcoidosis is characterized by the formation of small, granular inflammatory lesions (granulomas). The word "granuloma" comes from the Latin word "granum," meaning "grain" or "seed." Granulomas are characterized by a nodular appearance and a unique cellular pattern that can be seen through a microscope and can form on nearly any part of the body, internal or external. There are many different granulomatous diseases, from Crohn's disease to tuberculosis.
The cells that make up a granuloma are from the immune system. The immune system is the body's defense against disease and illness. Its major players are the macrophages and leukocytes, cells that originate in the bone marrow and travel through the lymphatic vessels to different areas of the body.
Macrophages are cells that attack foreign microbes by binding to and engulfing them. Macrophages secrete assorted biochemicals that affect the behavior of the surrounding cells. One of the types of biochemicals that they secrete, for example, are the cytokines, which cause inflammation. This is why an infected area becomes inflamed.
Lymphocytes are smaller immune cells that are inactive until they encounter an antigen (a foreign molecule) that they specifically recognize. They then start to secrete antibodies to fight the attacker. The two most common types of lymphocytes are T cells and B cells. The antibodies they secrete are known as immunoglobulins (Ig).
When foreign particles (e.g., bacteria, viruses, chemical toxins) resist the action of macrophages, the macrophages attack the resistant particle and form the characteristic cellular pattern known as a granuloma. The granuloma is a cluster of a variety of cells that forms a discrete nodule.
The multinucleated giant cell is characteristic of the granuloma. The giant cell is made up of many macrophages that fuse together and is seen in the central region of the granuloma. Many macrophages surround the giant cells and are called epitheliod cells. The central part of the granuloma is surrounded by layers of T cells. Granulomas can be easily seen and identified through a microscope.
Tuberculosis is a type of granulomatous disease. In tuberculosis, the centers of the granulomas become so isolated that the cells die from lack of oxygen and from the toxic effects of the macrophages and leukocytes that make up the granuloma. The dead tissue resembles a soft, cheesy substance, so the process is called caseation (caseation comes from the Latin word for "cheese").
Sarcoidosis, on the other hand, is noncaseating. The tissue in the middle of the granuloma does not die, and it does not resemble cheese. The presence of caseation eliminates sarcoidosis and suggests an infection such as tuberculosis or a fungal infection.
Granulomas spontaneously disappear without treatment, diminish with treatment, or persist. The physical presence of these granulomas can prevent the normal function of a variety of organs, such as the lungs, heart, and eyes.
Furthermore, these cells are activated and produce a variety of chemicals, including cytokines, that cause destruction of nearby tissue and abnormal healing. This abnormal healing, or scarring, of the tissue in the lungs is termed fibrosis.
Fibrosis in the lung causes irreparable damage, inhibiting it from functioning normally. Pulmonary fibrosis can be caused by a variety of underlying disorders, not just sarcoidosis. When it happens, depending on the extent of the fibrosis, the patient usually suffers a persistent cough, may experience shortness of breath, and may not be able to tolerate exercise.
Fortunately, most granulomas do not lead to fibrosis, but when they do, the fibrosis is irreversible. Even mild cases of sarcoidosis must be carefully monitored in case treatment is warranted.