Polymyositis
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Dermatomyositis/polymyositis p. 483
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for polymyositis/dematomyositis p. 483
Methotrexate p. 446
polymyositis/dematomyositis p. 483
Polymyositis
autoantibody p. 113
Polymyositis/dermatomyositis p. 483
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polymyositis/dermatomyositis p. 483
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In polymyositis, “myos-“ refers to the muscles, “poly-“ means many, and “-itis” refers to inflammation, so polymyositis is an inflammatory disorder which involves many muscle groups around the body.
Polymyositis is an immune- mediated disease, meaning that the immune system attacks the muscles in our own body.
Normally, the cells of the immune system are ready to spot and destroy anything foreign that could cause the body harm.
To help with this, most cells in the body have a set of proteins that combine together to form something called a major histocompatibility complex, or MHC, class I molecule that sits on the surface of their cell membrane.
These surface proteins act kind of like a serving platter, presenting molecules from within the cell for the immune system to continually sample.
Normally though the molecule’s just a sample from the cell, and the immune system recognizes it as harmless, and this is known as a self-antigen, and there’s no response.
But when a cell is actually invaded by a pathogen like a virus, viral antigens are presented on the MHC class I molecule, and that sparks a different immune response.
A type of T-lymphocyte, called a CD8+ T-cell, also known as a cytotoxic T-cell, uses its T-cell receptors to bind to the antigen presented by the MHC class I molecule.
If the cytotoxic T-cell binds strongly, than the antigen is recognized as foreign, and the cytotoxic T-cell secretes a whole lot of perforin and granzymes.
Perforin forms big holes in the infected cell and that allows the granzymes to enter the cell.
Once inside, the granzymes induce apoptosis, or programmed cell death.
As if that weren’t enough, the cytotoxic T-cells have a protein called Fas ligand on their surface, and it binds to a molecule called Fas on the surface of the infected cell.
Summary
Polymyositis is an inflammatory disorder of the muscles, caused mainly by cytotoxic T- cells destroying muscle tissue due to molecular mimicry and resulting in bilateral proximal muscle weakness of large muscle groups. It is characterized by muscle weakness, muscle pain, and difficulty with activities of daily living. Its diagnosis involves elevated serum creatinine kinase and myositis- specific antibodies, and it is treated with corticosteroids and specialized physical exercise.
Sources
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "Polymyositis-dermatomyositis: a clinical review." Postgraduate Medical Journal (1989)
- "Cardiac Involvement in Adult Polymyositis or Dermatomyositis: A Systematic Review" Clinical Cardiology (2012)
- "Diagnosis of dermatomyositis and polymyositis: a study of 102 cases" Arquivos de Neuro-Psiquiatria (2000)
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