differential diagnosis of intramuscular high STIR signal on MRI

The presence of intramuscular edema (increased high T2/STIR signal) on MRI carries an extremely broad differential. They include:

trauma
- effects of direct injury or tear
- denervation injury: denervation changes in muscles
early myositis ossificans
inflammatory myopathies
- dermatomyositis
- polymyositis
- inclusion body myositis
- eosinophilic myositis
- proliferative myositis
- myositis associated with connective tissue diseases
  - systemic lupus erythematosus (SLE)
  - Sjögren syndrome
  - overlap syndrome
  - scleroderma
  - mixed connective tissue disease
infective myositis including pyomyositis and viral myositis
inherited myopathies (e.g. Duchenne muscular dystrophy, sarcoglycanopathies, or dysferlinopathies)
infiltrating neoplasm, e.g. muscle lymphoma
acute or subacute phase of autoimmune neuropathy, e.g. Parsonage-Turner syndrome (in the shoulder)
rhabdomyolysis
- drug-induced
- intravenous heparin therapy
- trauma
- burns
- toxins
- autoimmune inflammation
vascular causes
- muscle infarction
  - microvascular disease, e.g. diabetes mellitus
- Behçet disease
- sickle cell crisis
overuse
- delayed onset muscle soreness (DOMS)