Sarcoidosis at a Glance
- Sarcoidosis is a systemic granulomatous disease of unknown cause that primarily affects the lungs, but often involves the skin.
- The highest prevalence of sarcoidosis is in Denmark and Sweden; in the United States, it is higher in persons of African descent.
- The most common sites of cutaneous sarcoidosis are the head and neck. Scar tissue at all sites can be affected.
- The most common cutaneous form of sarcoidosis, the papular form, is characterized by translucent yellow-red papules with an “apple jelly” appearance on diascopy.
- Noncaseating, “naked” granulomas on biopsy are quite suggestive, but not specific for the diagnosis.
- Erythema nodosum is the main nonspecific cutaneous manifestation of sarcoidosis, and heralds a good prognosis.
Sarcoidosis is a multisystem granulomatous disease of unknown cause. The lung is the most commonly affected organ, but the skin is frequently involved.1 The first descriptions of sarcoidosis in the late 1800s were limited to its skin manifestations.1 The term sarcoidosis is derived from Caesar Boeck's 1899 report of what he described as “multiple benign sarkoid of the skin,” because he believed the lesions resembled sarcomas but were benign.2
Sarcoidosis occurs worldwide and affects all ages and races. Disease onset is most often in the third decade of life, although a smaller second peak occurs in people older than 50 years.1 The prevalence rate is slightly higher in women.1 Sarcoidosis is more frequent away from the equator. The highest prevalence of sarcoidosis is found in Caucasians in Denmark, Sweden, and, in the United States, in persons of African descent.1 In the United States, the lifetime risk of sarcoidosis is 2.4% in African-Americans and 0.85% in Caucasians.3 The age-adjusted annual incidence rate of sarcoidosis in the United States is 35.5 per 100,000 for African-Americans and 10.9 per 100,000 for Caucasians.3 The frequency and severity of the disease also vary between different ethnicities and races. African-Americans tend to have more severe disease, whereas Caucasians are more likely to present with asymptomatic disease.4,5 African-Americans are also more likely to have extrapulmonary disease,6 require treatment,7 develop new organ involvement,8 and have a lower rate of clinical recovery than Caucasians.5,8 The disease is more common in life-long nonsmokers.9
The current understanding is that the development of sarcoidosis requires at least three major events: (1) exposure to antigen(s), (2) acquired cellular immunity directed against the antigen and mediated through antigen-presenting cells and antigen-specific T lymphocytes, and (3) the appearance of immune effector cells that promote a nonspecific inflammatory response.10 The identity of the putative antigen(s) of sarcoidosis is unknown.
Presumably, antigen-presenting cells such as macrophages recognize, process, and present the processed antigen to CD4+ T cells of the T helper 1 type (Fig. 152-1). The processed antigen is presented to these lymphocytes via HLA class II molecules on the ...