Polymyositis and dermatomyositis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]
Overview
The exact pathogenesis of polymyositis and dermatomyositis is not fully understood. However, it is understood that polymyositis and dermatomyositis are the result of autoimmune attack but triggering factors are not well-known. Polymyositis is caused by inflammation and degeneration of the muscles. In polymyositis, CD8-positive cytotoxic T cells invade muscle fibers that express MHC class I antigens which may leads to fiber necrosis via the perforin pathway. Hypoxia may reduce creatine phosphate and adenosine triphosphate (ATP) levels in muscle and lead to fatigue and muscle weakness. Dermatomyositis is caused by skin inflammation. In dermatomyositis, activation and deposition of complements may lead to lysis of endomysial capillaries and muscle ischemia. Genes including HLA DRB1*0301 and HLA DQA1*0501 alleles, and tumour necrosis factor 308A might be associated with development of polymyositis and dermatomyositis, especially in familial cases. Different conditions associated with polymyositis and dermatomyositis include respiratory and cardiac diseases, other connective tissue diseases, and malignancies. On microscopic histopathological analysis, partial invasion of lymphocytes within the muscle fibers and regenerating fibers with enlarged nuclei are characteristic findings of polymyositis.
Pathophysiology
Pathogenesis
The exact pathogenesis of polymyositis and dermatomyositis is not fully understood. However, it is understood that polymyositis and dermatomyositis are the result of autoimmune attack but triggering factors are not well-known.[1][2][3][4][5]
Polymyositis
- Polymyositis is caused by inflammation and degeneration of the muscles.
- In polymyositis, CD8-positive cytotoxic T cells invade muscle fibers that express MHC class I antigens which may lead to fiber necrosis via the perforin pathway.
- Hypoxia may reduce creatine phosphate and adenosine triphosphate (ATP) levels in muscle and lead to fatigue and muscle weakness.
- Interleukin (IL) 21, tumor growth factor-b (TGF-b), and high-mobility group protein 1 (HMG-1) induce muscle fatigue by decreasing Ca release.
Dermatomyositis
- Dermatomyositis is caused by skin inflammation.[6][7][8][9]
- In dermatomyositis, activation and deposition of complements may lead to lysis of endomysial capillaries and muscle ischemia.[4]
Genetics
- Genes might be associated with development of polymyositis and dermatomyositis, especially in familial cases, which include:[10]
- HLA DRB1*0301 alleles for polymyositis and inclusion-body myositis
- HLA DQA1*0501 for juvenile dermatomyositis,
- Tumour necrosis factor 308A polymorphism for photosensitivity in dermatomyositis
Associated Conditions
Different conditions associated with polymyositis and dermatomyositis include:
- Interstitial lung disease
- Conduction abnormalities and arrhythmia
- Myocardial infarction
- Other connective tissue diseases like
- Malignancies are as follows:
| Association | Polymyositis | Dermatomyositis |
|---|---|---|
| Malignancy | 5-7 fold more risks than the general population |
Microscopic Pathology
- On microscopic histopathological analysis of polymyositis, partial invasion of lymphocytes within the muscle fibers and regenerating fibers with enlarged nuclei are characteristic findings.
- On microscopic histopathological analysis of dermatomyositis, perifascicular inflammation with perifascicular atrophy and loss of vessels around muscle fibers are characteristic findings.
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References
- ↑ Khan, Sabiha; Christopher-Stine, Lisa (2011). "Polymyositis, Dermatomyositis, and Autoimmune Necrotizing Myopathy: Clinical Features". Rheumatic Disease Clinics of North America. 37 (2): 143–158. doi:10.1016/j.rdc.2011.01.001. ISSN 0889-857X.
- ↑ Dobloug, Cecilie; Garen, Torhild; Bitter, Helle; Stjärne, Johan; Stenseth, Guri; Grøvle, Lars; Sem, Marthe; Gran, Jan Tore; Molberg, Øyvind (2015). "Prevalence and clinical characteristics of adult polymyositis and dermatomyositis; data from a large and unselected Norwegian cohort". Annals of the Rheumatic Diseases. 74 (8): 1551–1556. doi:10.1136/annrheumdis-2013-205127. ISSN 0003-4967.
- ↑ Chinoy, H.; Fertig, N.; Oddis, C. V; Ollier, W. E R; Cooper, R. G (2007). "The diagnostic utility of myositis autoantibody testing for predicting the risk of cancer-associated myositis". Annals of the Rheumatic Diseases. 66 (10): 1345–1349. doi:10.1136/ard.2006.068502. ISSN 0003-4967.
- ↑ 4.0 4.1 Dalakas, Marinos C; Hohlfeld, Reinhard (2003). "Polymyositis and dermatomyositis". The Lancet. 362 (9388): 971–982. doi:10.1016/S0140-6736(03)14368-1. ISSN 0140-6736.
- ↑ Douglas, William W.; Tazelaar, Henry D.; Hartman, Thomas E.; Hartman, Robert P.; Decker, Paul A.; Schroeder, Darrell R.; Ryu, Jay H. (2001). "Polymyositis–Dermatomyositis-associated Interstitial Lung Disease". American Journal of Respiratory and Critical Care Medicine. 164 (7): 1182–1185. doi:10.1164/ajrccm.164.7.2103110. ISSN 1073-449X.
- ↑ Bodoki L, Nagy-Vincze M, Griger Z, Betteridge Z, Szöllősi L, Dankó K (December 2014). "Four dermatomyositis-specific autoantibodies-anti-TIF1γ, anti-NXP2, anti-SAE and anti-MDA5-in adult and juvenile patients with idiopathic inflammatory myopathies in a Hungarian cohort". Autoimmun Rev. 13 (12): 1211–9. doi:10.1016/j.autrev.2014.08.011. PMID 25182203.
- ↑ Tiniakou E, Mammen AL (February 2017). "Idiopathic Inflammatory Myopathies and Malignancy: a Comprehensive Review". Clin Rev Allergy Immunol. 52 (1): 20–33. doi:10.1007/s12016-015-8511-x. PMID 26429706.
- ↑ Bohan, Anthony; Peter, James B. (1975). "Polymyositis and Dermatomyositis". New England Journal of Medicine. 292 (8): 403–407. doi:10.1056/NEJM197502202920807. ISSN 0028-4793.
- ↑ Adler BL, Christopher-Stine L (February 2018). "Triggers of inflammatory myopathy: insights into pathogenesis". Discov Med. 25 (136): 75–83. PMID 29579414.
- ↑ Dalakas, Marinos C; Hohlfeld, Reinhard (2003). "Polymyositis and dermatomyositis". The Lancet. 362 (9388): 971–982. doi:10.1016/S0140-6736(03)14368-1. ISSN 0140-6736.
- ↑ "File:Neuropathology case XII 01.jpg - Libre Pathology".
- ↑ "File:Neuropathology case XII 03.jpg - Libre Pathology".
- ↑ "File:Dermatomyositis c5b9.jpg - Libre Pathology".
