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Graduate Medical Education; Department of Medicine, Division of Rheumatology

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Book Chapter


Immune System Diseases | Musculoskeletal Diseases | Rheumatology


Idiopathic inflammatory myositis (IIM) is classified into 4 subtypes based on clinical and histopathological features. Polymyositis and dermatomyositis (PM/DM) are 2 of those subtypes in addition to immune-mediated necrotizing myopathy and inclusion body myositis. The presence of autoantibodies and inflammatory infiltration in the muscles suggests that idiopathic inflammatory myositis is an autoimmune condition, but the target autoantigens have not yet been identified. Apart from symmetric proximal muscle weakness, polymyositis and dermatomyositis have several clinical manifestations in common when compared to inclusion body myositis and necrotizing myopathy and can be grouped for discussion. The most commonly used criteria for PM/DM are Peter/Bohan Criteria.[1]: 1. Symmetric proximal muscle weakness. 2. Elevated serum muscle enzymes. 3. Myopathic changes in electromyography (EMG). 4. Characteristic muscle biopsy abnormalities. 5. Typical rash of dermatomyositis for diabetes mellitus.


polymyositis, dermatomyositis, autoimmune disorders

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Copyright © 2018, StatPearls Publishing LLC. This book is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits use, duplication, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, a link is provided to the Creative Commons license, and any changes made are indicated.


Cheeti A, Panginikkod S. Dermatomyositis And Polymyositis. [Updated 2018 Oct 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available from:

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.



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