Sarcoidosis is a multisystem disease characterized by non-caseating granuloma formation. Although the lungs are involved in 90% of patients, sarcoidosis can occur in the lymph nodes, eyes, and skin as well. Sarcoidosis occurs in adults younger than 40 years of age with a higher incidence in the Danish and Swedish population and among US African Americans. Sarcoidosis is one of the few pulmonary diseases with a higher prevalence among nonsmokers. It has been suggested that sarcoidosis is a disease characterized by an abnormal immune response to certain environmental agents in genetically predisposed individuals. In very recent research published in March 2017 conducted by Sweden’s Center for Allogeneic Stem Cell Transplantation (CAST), blood samples from individuals with sarcoidosis, Löfgren’s syndrome, an acute form of sarcoidosis, and tuberculosis were tested for peptides of Mycobacterium tuberculosis. The results of the study have confirmed that the bacteria, Mycobacterium
tuberculosis that causes tuberculosis, is also involved in sarcoidosis development. Since the immune response between patients with sarcoidosis and tuberculosis is different, researchers speculate that genetic factors may determine how the body responds to an M. tuberculosis encounter whether the body is able to control bacterial growth or whether sarcoidosis or tuberculosis will develop.
In response to the mycobacteria, the immune systems of sarcoidosis patients develop a cell-mediated response to the “antigens” driven by CD4+ helper T cells. The compact collection of epithelioid cells which contain agents such as mycobacteria are rimmed by an outer zone of largely CD4+ T cells and laminated by fibroblasts. Over time, the fibroblast proliferate and lay down collagen which replaces the granulomas with hyalinized scars. The granulomas predominantly involve the interstitium rather than airspaces of the lung. In 10% to 15% of patients, the granulomas are eventually replaced by diffuse interstitial fibrosis resulting in honeycombed lungs.
The granulomas in the lungs can damage the normal lung tissue resulting in symptoms of shortness of breath, dry cough, and fatigue. Skin lesions are encountered in approximately 25% of patients. The hallmark of acute sarcoidosis is erythema nodosum consisting of raised, red, tender nodules on the anterior of the legs. Involvement of eyes occurs in 25% to 50% of patients. 75% to 90% of patients have enlarged intrathoracic hilar and paratracheal lymph nodes. 75% of patients have granulomas in their spleen and granulomas lesions in their liver. As many as 40% of patients’ bone marrow is also involved. Constitutional signs and symptoms include fever, fatigue, weight loss, anorexia, and night sweats.