Overview of idiopathic inflammatory myopathies

Ashton, 2021Needham, 2016Pipitone, 2020Schmidt, 2018Vencovsky, 2019

Idiopathic inflammatory myopathies are a heterogeneous group of rare disorders that are seen in adults, children and adolescents, and mainly affect skeletal muscle. Childhood disease differs from adult disease in that it is not usually associated with malignancy; for details on Juvenile dermatomyositis, see the separate topic. For details on classification of idiopathic inflammatory myopathies, see Classification of idiopathic inflammatory myopathies, which includes:

  • dermatomyositis
  • polymyositis
  • necrotising autoimmune myopathy (NAM)
  • overlap myositis
  • myositis of antisynthetase syndrome
  • inclusion body myositis (IBM).

People usually present with proximal muscle weakness that progresses over weeks. The bulbar, respiratory and cardiac muscles can also be involved. An elevated serum creatine kinase (CK) concentration is often indicative of a myopathy in people presenting with proximal muscle weakness.

Suspect an idiopathic inflammatory myopathy based on clinical history and examination; important features include the tempo of disease, pattern of muscle weakness and presence of associated features (eg cutaneous eruptions, Raynaud phenomenon, arthritis, interstitial lung disease [pulmonary fibrosis])—see Clinical features of idiopathic inflammatory myopathies.

Note: Refer patients with a suspected idiopathic inflammatory myopathy, especially severe proximal weakness, dysphagia and risk of aspiration, urgently to a specialist centre.

Management for idiopathic inflammatory myopathies is usually under specialist supervision. Refer patients with a suspected idiopathic inflammatory myopathy, especially severe proximal weakness, dysphagia and risk of aspiration, urgently to a specialist centre.

Inclusion body myositis is managed differently from the other inflammatory myopathies; see Specific management for inclusion body myositis.