Sarcoidosis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Pathophysiology
No direct cause of sarcoidosis has been identified, although there have been reports of cell wall deficient bacteria that may be possible pathogens.[1] These bacteria are not identified in standard laboratory analysis. It has been thought that there may be a hereditary factor because some families have multiple members with sarcoidosis. To date, no reliable genetic markers have been identified, and an alternate hypothesis is that family members share similar exposures to environmental pathogens. There have also been reports of transmission of sarcoidosis via organ transplants.[2].
Sarcoid granulomas are suggested to have formed with HLA-mediated processing of antigens by macrophages.[3]. The process is driven by CD4+ helper T cells. There is increased levels of T cell–derived TH1 cytokines such as IL-2 and IFN-γ, resulting in T-cell expansion and macrophage activation, respectively. Increased levels of several cytokines in the local environment (IL-8, TNF, macrophage inflammatory protein 1α) that favor recruitment of additional T cells and monocytes and contribute to the formation of granulomas. TNF in particular is released at high levels by activated alveolar macrophages.[4][5]
Sarcoidosis frequently causes a dysregulation of vitamin D production with an increase in extrarenal (outside the kidney) production.[6] Specifically, macrophages inside the granulomas convert vitamin D to its active form, resulting in elevated levels of the hormone 1,25-dihydroxyvitamin D and symptoms of hypervitaminosis D that may include fatigue, lack of strength or energy, irritability, metallic taste, temporary memory loss or cognitive problems. Physiological compensatory responses (e.g. suppression of the parathyroid hormone levels) may mean the patient does not develop frank hypercalcemia.
Sarcoidosis has been associated with celiac disease. Celiac disease is a condition in which there is a chronic reaction to certain protein chains, commonly referred to as glutens, found in some cereal grains. This reaction causes destruction of the villi in the small intestine, with resulting malabsorption of nutrients.
While disputed, some cases have been determined to be caused by inhalation of the dust from the collapse of the World Trade Center after the September 11, 2001 attacks.[7] See Health effects arising from the September 11, 2001 attacks for more information.
Gallium-67 citrate is useful for diagnosing suspected sarcoidosis and evaluation of treatment response. It is more sensitive than radiographic images on diagnosis of Sarcoidosis.
Histopathological Findings
References
- ↑ Almenoff PL, Johnson A, Lesser M, Mattman LH. Growth of acid fast L forms from the blood of patients with sarcoidosis. Thorax 1996;51:530-3. PMID 8711683.
- ↑ Padilla ML, Schilero GJ, Teirstein AS. Donor-acquired sarcoidosis. Sarcoidosis Vasc Diffuse Lung Dis 2002;19:18-24. PMID 12002380.
- ↑ Goldman's Cecil Medicine,24th Edition.
- ↑ Kumar: Robbins and Cotran Pathologic Basis of Disease, Professional Edition, 8th ed.
- ↑ Chen ES, Moller DR, Medscape (2011). "Sarcoidosis--scientific progress and clinical challenges". Nat Rev Rheumatol. 7 (8): 457–67. doi:10.1038/nrrheum.2011.93. PMID 21750528.
- ↑ Barbour GL, Coburn JW, Slatopolsky E, Norman AW, Horst RL. Hypercalcemia in an anephric patient with sarcoidosis: evidence for extrarenal generation of 1,25-dihydroxyvitamin D. N Engl J Med 1981;305:440-3. PMID 6894783.
- ↑ New York Times article, May 24, 2007