Features Associated with Inflammatory Myopathies
| Characteristic | Polymyositis | Dermatomyositis | Inclusion Body Myositis |
|---|---|---|---|
| Age at onset | >18 years | Adulthood and childhood | >50 years |
| Familial association | No | No | Yes, in some rare cases |
| Extramuscular manifestations | Yes | Yes | Yes |
| Associated conditions | |||
| Connective tissue diseases | Yesa | Scleroderma and mixed connective tissue disease (overlap syndromes) | Yes, in up to 20% of casesa |
| Systemic autoimmune diseasesb | Frequent | Infrequent | Infrequent |
| Malignancy | No | Yes, in up to 15% of cases | No |
| Viruses | Yesc | Unproven | Yesc |
| Drugsd | Yes | Yes, rarely | No |
| Parasites and bacteriae | Yes | No | No |
aSystemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome, systemic sclerosis, mixed connective tissue disease.
bCrohn's disease, vasculitis, sarcoidosis, primary biliary cirrhosis, adult celiac disease, chronic graft-versus-host disease, discoid lupus, ankylosing spondylitis, Behçet's syndrome, myasthenia gravis, acne fulminans, dermatitis herpetiformis, psoriasis, Hashimoto's disease, granulomatous diseases, agammaglobulinemia, monoclonal gammopathy, hypereosinophilic syndrome, Lyme disease, Kawasaki disease, autoimmune thrombocytopenia, hypergammaglobulinemic purpura, hereditary complement deficiency, IgA deficiency.
cHIV (human immunodeficiency virus) and HTLV-1 (human T cell lymphotropic virus type 1).
dDrugs include penicillamine (dermatomyositis and polymyositis), zidovudine (polymyositis), statins (necrotizing, toxic, or autoimmune myositis), and contaminated tryptophan (dermatomyositis-like illness). Other myotoxic drugs may cause myopathy but not an inflammatory myopathy (see text for details).
eParasites (protozoa, cestodes, nematodes), tropical and bacterial myositis (pyomyositis).