Diagnosis: Sarcoidosis
Sarcoidosis is an idiopathic systemic disorder identified by noncaseating granulomas in affected organs. Clinical presentation is variable and can involve virtually any organ system. Because of this, sarcoidosis is often misdiagnosed. The diagnosis of sarcoidosis requires clinical and radiographic features known to be associated with sarcoidosis, noncaseating granulomas found on tissue biopsy, and exclusion of known causes of granulomatous diseases such as tuberculosis or berylliosis.1
Sarcoidosis most commonly affects adults in their third decade of life.2 It is unusual to see the initial presentation of sarcoidosis after the age of 40 years—except in Scandinavia and Japan, where a second peak occurs among women after age 50 years.3,4,5 There seems to be a slightly higher rate of sarcoidosis in women.1 The incidence of sarcoidosis is higher in Swedes, Danes, and African Americans. The lifetime risk of sarcoidosis is 0.85% for US whites and 2.4% for US blacks.6
Possible causes of sarcoidosis
Although the cause of sarcoidosis is unknown, there is evidence of spatial, seasonal (winter and early spring), and familial clustering. Multiple theories have been proposed suggesting possible transmissible agents as the cause of sarcoidosis, including infectious agents such as Mycoplasma and Borrelia burgdorferi.
Other proposed agents include metals and inorganic substances such as clay and pine tree pollen.10 Despite extensive research, these hypotheses have not been validated. None-theless, there seems to be an emerging pattern of immunologic abnormalities in patients with sarcoidosis, suggesting an abnormal host response.
Clinical presentation of sarcoidosis
The local Th1-type T lymphocyte is now believed to be the central cell responsible for granuloma formation.10 It is hypothesized that sarcoid granulomas are formed in response to chronic antigenic stimulation of genetically susceptible Th-1 T cells and subsequent macrocyte-mediated inflammation.10,11 Certain HLA haplotypes have been implicated in the pathogenesis of sarcoidosis, yet there is no consistent data linking any one haplotype to the disease.11
The clinical presentation of sarcoidosis is related to the organ(s) involved. Specifically, symptoms may be a result of granuloma mass-effect, immune complex vasculitis, metabolically active granulomas, or fibrotic organ destruction. The lungs are the most commonly affected organ and lung involvement is seen in 88% of patients diagnosed with sarcoidosis.1
The most common presentation of intrathoracic sarcoidosis is bilateral hilar lymphadenopathy with or without diffuse pulmonary infiltration. This may present clinically as cough, wheeze, shortness of breath, or dyspnea on exertion.