Idiopathic inflammatory myopathies (symptoms, diagnosis, treatment, classification)

1. Big picture

Idiopathic inflammatory myopathies (IIMs) are systemic autoimmune muscle diseases. The examiner usually wants four things:

1. Recognize proximal muscle weakness, not just pain.
2. Classify the subtype: dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, inclusion body myositis, antisynthetase syndrome.
3. Confirm with muscle enzymes, autoantibodies, MRI/EMG, and biopsy when needed.
4. Treat with glucocorticoids + steroid-sparing immunosuppression, but remember that inclusion body myositis responds poorly.

IIMs are multisystem diseases: muscle, skin, lung, joints, heart, gastrointestinal tract, and malignancy risk may all matter. The British Society for Rheumatology guideline describes IIM as a multisystem autoimmune condition with muscle inflammation, interstitial lung disease, and skin manifestations. ([OUP Academic][1])

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