Sarcoidosis is a rare inflammatory disease characterized by the abnormal formation of clumps of immune cells, called granulomas, that build up in organs and tissues. The granulomas can form anywhere in the body, and disrupt the normal functions of organs. The organ most frequently affected by sarcoidosis is the lungs, occurring in about 90 percent of patients.
A diagnosis of sarcoidosis often can be done using one of several imaging tests. These tests produce an image of the affected area and may be used to assign a stage to the disease. This is known as the Siltzbach classification system.
Siltzbach classification system
The Siltzbach classification system ranges from stage 0 to 5 based on the location of the granulomas. The staging is determined using a chest X-ray, or radiography, an imaging test that uses low doses of radiation to form an image of the structures in the chest. The granulomas can be seen in this image.
The classification concerns only granulomas present in the lymph nodes and the lungs. Lymph nodes act to filter any harmful substances from the body, and produce certain immune cells. There are lymph nodes throughout the body, but most commonly affected are the so-called hilar and mediastinal lymph nodes in the lungs, and the paratracheal lymph nodes in the neck.
The five stages of pulmonary sarcoidosis are:
- Stage 0 (no pulmonary sarcoidosis): no sign of granulomas in the lungs or lymph nodes
- Stage 1 (lymphadenopathy): granulomas present in the lymph nodes only
- Stage 2 (lymphadenopathy and pulmonary infiltrates): granulomas present in both the lymph nodes and lungs
- Stage 3 (pulmonary infiltrates): granulomas present in the lungs only
- Stage 4 (pulmonary fibrosis): scarring of the lung tissue and permanent damage
Unlike many diseases, the consecutive numbered stages for sarcoidosis do not indicate disease progression, but rather the areas affected by it.
The granulomas may dissipate on their own (known as spontaneous remission) or following treatment, which can result in the patient moving between stages. The later stages tend to be associated with more severe symptoms and worse lung function, but this can vary among patients.
The disease is generally more likely to go into spontaneous remission in the earlier stages, seen in about 60-90 percent of patients in stage 1, 40-70 percent of patients in stage 2, 10-20 percent of patients in stage 3, and in no patients in stage 4.
If the patient is diagnosed at stage 4, it means that permanent damage to the lungs has occurred; even if the granulomas are removed, the patient still will experience the symptoms of pulmonary fibrosis. This is the only irreversible stage.
Staging sarcoidosis in this way is used in the U.S., but is currently not a common practice in the U.K.
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