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Inflammatory Myopathies

Greg Jackson


  • Inflammation and damage of skeletal muscle primarily leading to weakness

  • Subtypes: Dermatomyositis, polymyositis, antisynthetase antibody syndrome associated myositis, immune-mediated necrotizing myositis, inclusion body myositis

  • Additional myopathies: statin-induced myopathy, metabolic (hypothyroid, electrolyte), viral/infection myositis, diabetic myonecrosis

  • Important point: PMR= painful, preserved strength vs inflammatory myopathy = painless weakness

  • Hypomyopathic (or amyopathic) variants: skin and/or lungs are affected >> muscles


  • Proximal, symmetric muscle weakness in upper and lower extremities in all but inclusion body myositis which is typically more distal and asymmetric

  • Dermatomyositis: skin involvement can include heliotrope rash of upper eyelids, Gottron’s papules (on MCP, PIP), “mechanic’s hands,” and shawl sign

  • Raynaud’s and arthralgias can also be present


  • Labs: BMP, TSH, CK level, anti Jo-1 antibody

  • EMG: findings indicate myopathy

  • MRI extremity/affected muscle group: muscle edema

  • Skin biopsy in dermatomyositis: “interface dermatitis.”

  • Muscle biopsy (do not do biopsy in same muscle as EMG done)

    • Polymyositis, inclusion body myositis: T cell mediated muscle injury

    • Dermatomyositis: immune complex/B cell mediated muscle injury


  • Prednisone 1 mg/kg/day for 4-6 weeks with subsequent taper

  • Consult Rheumatology

  • MTX or AZA used if refractory to steroids, may need IVIG, rituximab

  • If statin induced: stop statin or switch to lower intensity

  • If dermatomyositis: evaluate for underlying malignancy

Last update: 2022-06-27 03:27:41