- Systemic disease due to noncaseating epithelioid granulomatous inflammation in affected organs.
- Most frequently affected organs are lung, lymph nodes, eyes, skin, joints, liver, muscles, central and peripheral nervous system, upper airway, heart, and kidneys.
- Clinically apparent organ involvement is typically restricted to a few organs, usually defined early in the course of disease.
- In the United States, sarcoidosis is more common and severe in blacks.
- Diagnosis requires a compatible clinical picture and a biopsy with typical noncaseating granulomas, excluding diseases that can cause similar granulomatous reactions.
Sarcoidosis is found worldwide with a prevalence ranging from 10 to 80 cases per 100,000 in North America and Europe. Higher regional prevalence has been reported in Scandinavia and the southeast coastal United States. In the United States, one study from a Midwest city estimated that the lifetime risk of developing sarcoidosis was 2.7% in black women, 2.1% in black men, 1% in white women, and 0.8% in white men. Worldwide, there is a slight female predominance. Although all ages can be affected, most cases occur between the ages of 20 and 40 years, with a second peak incidence in women over age 60.
A genetic predisposition to sarcoidosis is supported by familial clustering in approximately 5–10% of cases of sarcoidosis. A recent multicenter study on the etiology of sarcoidosis in the United States (A Case-Control Etiologic Study of Sarcoidosis [ACCESS]) suggests that the familial relative risk is approximately 5.0 among first-degree relatives, and this risk is higher in white families compared with black families.
The strongest associations between genotype and sarcoidosis risk have been identified within the major histocompatibility (MHC) locus on chromosome 6. Two recent genome-wide linkage analyses identified an association with the butyrophilin-like 2 gene (BTNL2) (located within the MHC locus) in both whites and blacks with sarcoidosis.
The cause of sarcoidosis is uncertain. The genetic pattern of inheritance suggests that susceptibility to sarcoidosis is polygenic and interacts importantly with environmental factors. Geographic differences in disease prevalence and reports of time-space clustering of cases have also suggested that sarcoidosis may be associated with an environmental, likely microbial, exposure. The large, multicenter study ACCESS found no evidence for a single dominant environmental or occupational exposure associated with an increased risk of developing sarcoidosis. Multiple regression analyses found positive associations with modest odds ratios of approximately 1.5 for exposures to molds and mildews, insecticides, or musty odors at work. The ACCESS data supported a negative association of tobacco use or tobacco smoke exposure among sarcoidosis patients.
Since the first description of sarcoidosis, many experts have speculated that a potential microbial cause of sarcoidosis exists. Recent studies using polymerase chain reaction (PCR) have associated mycobacterial and propionibacterial organisms as possible etiologic factors for sarcoidosis. A recent meta-analysis concluded that 26% of sarcoidosis tissues contained mycobacterial nucleic acids, with an odds-ratio of ...