Myositis (plural: myositides) is the subset of myopathy characterised by inflammation of skeletal muscle.
Pathology
Aetiology
Myositides can be generally categorised by aetiology as follows 1:
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inflammatory myositis
overlap myositis (myositis associated with connective tissue diseases) 5
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chronic graft versus host disease 2
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bacterial myositis (pyomyositis)
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viral myositis
influenza myositis
coxsackievirus B virus-related pleurodynia (Bornholm disease)
virus-associated rhabdomyolysis
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parasitic myositis (a cause of eosinophilic myositis)
fungal myositis (rare)
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drug-related myositis
statin-related myositis
immune checkpoint inhibitor-related myositis
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trauma or iatrogenic myositis
Radiographic features
MRI is the gold standard modality for non-invasive evaluation of myositis, which shows a classic oedema signal pattern (high T2WI and STIR signal) in affected muscles. Inflamed muscles demonstrate contrast enhancement.
If chronic, T1WI will show high muscle signal indicating fat replacement and atrophy.