Last reviewed: 4 Jul 2021
Last updated: 18 May 2021

Summary

Definition

History and exam

Key diagnostic factors

  • difficulty with motor tasks
  • muscle weakness
  • muscle atrophy
  • heliotrope rash with eyelid edema
  • Gottron papules

Other diagnostic factors

  • frequent falls
  • fatigue and generalized malaise
  • weight loss
  • shortness of breath
  • mild fever
  • abnormal breath sounds
  • dysphagia
  • myalgia
  • arthralgia
  • palpitations
  • syncope
  • facial rash
  • erythematous rash
  • nail fold changes
  • facial muscle weakness
  • skin calcinosis
  • joint swelling
  • arrhythmias
  • signs of heart failure and/or myocardial infarction
  • physical findings of malignancy
  • systemic signs of autoimmune disease
  • peripheral neuropathy

Risk factors

  • age >40 years
  • exposure to high intensity of global UV radiation
  • genetic predisposition
  • female sex and/or black ethnicity (polymyositis and dermatomyositis)
  • male sex and/or white ethnicity (inclusion body myositis)
  • lipid-lowering agents
  • HIV
  • viral infections (excluding HIV)
  • nonviral infection
  • vaccination
  • D-penicillamine
  • other drugs or toxins

Diagnostic investigations

1st investigations to order

  • creatine kinase
  • electromyograph
  • muscle biopsy
  • myositis-specific and associated autoantibodies
  • magnetic resonance imaging
  • aldolase
  • lactate dehydrogenase
  • alanine aminotransferase
  • aspartate aminotransferase
  • myoglobin

Investigations to consider

  • erythrocyte sedimentation rate
  • C-reactive protein
  • antinuclear antibodies
  • serum creatinine
  • serum ferritin
  • fluorodeoxyglucose positron emission tomography (FDG-PET)/computed tomography

Treatment algorithm

Contributors

Authors

Hector Chinoy, PhD, FRCP, BMBS, MSc, BMedSci

Professor of Rheumatology and Neuromuscular Disease

National Institute for Health Research Manchester Biomedical Research Centre

Manchester University NHS Foundation Trust

The University of Manchester

Manchester

UK

Disclosures

HC has received advisory board/lecture fees from Lilly, UCB, Janssen, and Biogen; has done consultancy work for Novartis and Momenta; has received travel expenses from Abbvie, Janssen, and Eli Lilly; and has received research grants from UCB and MedImmune. He is also an author of several references cited in this topic.

James Lilleker, PhD, MBChB

Clinical Lecturer in Neurology

Centre for Musculoskeletal Research

Division of Musculoskeletal and Dermatological Sciences

The University of Manchester

Manchester

Neurology Registrar

Manchester Centre for Clinical Neuroscience

Salford Royal NHS Foundation Trust

Manchester Academic Health Sciences Centre

Salford

UK

Disclosures

JL is an author of several references cited in this topic.

Acknowledgements

Dr Hector Chinoy and Dr James Lilleker would like to gratefully acknowledge Dr Nizar Souayah, the previous contributor to this topic.

Disclosures

NS declares that he has no competing interests.

Peer reviewers

Sami Khella, MD

Physician

Department of Neurology

Penn Presbyterian Medical Center

University of Pennsylvania Health System

Philadelphia

PA

Disclosures

SK declares that he has no competing interests.

Anthony Arnold Amato, MD

Vice-Chairman

Department of Neurology

Brigham and Women's Hospital

Harvard Medical School

Boston

MA

Disclosures

AAA declares that he has no competing interests.

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