Sarcoidosis: Pathogenesis and chest X-Ray findings
Authors: Harshil Shah Reviewers: Mao Ding Tara Shannon Vincent Dinculescu* * MD at time of publication
Genetic predisposition
Unknown sarcoid antigens
Sarcoid antigens interact with pattern recognition receptors on macrophages in the lungs
Macrophages become activated
Helper T cells and macrophages release cytokines (proteins made by immune cells that modulate cell growth and division) such as tumor necrosis factor to neighboring cells
Tumor necrosis factor is a pro- inflammatory cytokine promoting cell survival and proliferation, predominantly in the upper/middle lung for unknown causes
More macrophages and helper T cells are activated and accumulate in the mediastinum, peritracheal region, and the upper/middle lung
Macrophages and helper T cells promote fibroblasts (cells that produce collagen) in the upper and middle lungs
Macrophages in the lungs present the antigen to the helper T cells in lymph nodes
Helper T cells become activated and accumulate in the lungs
Image Credit: Radiopaedia
The right peritracheal and bilateral hilar lymph nodes becomes swollen
Inflammatory signals stimulate macrophages to form granulomas (clusters of white blood cells) in the lungs, peritracheal and bilateral hilar lymph nodes
X-ray images show visible white opacities in areas of increased densities, such as areas of macrophage and helper T cell concentration
Enlarged peritracheal lymph node Stage 1 and 2
Enlarged bilateral hilar lymph node Stage 1 and 2
Interstitial Opacities Stage 2 and 3
Bilateral and symmetric lacey lung markings in upper/middle lungs
Decreased lung volume on either sides (higher than normal diaphragm)
Collagen accumulate which causes fibrotic tissue (scarred and thickened), replacing healthy tissue
Pulmonary fibrosis of upper and middle lung Stage 4
The fibrotic tissue is stiffer, reduces amount of air held in lungs, and has a higher density (appearing white)
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Published April 7, 2023 on www.thecalgaryguide.com