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Idiopathic inflammatory myopathies: when to suspect one and what to do about it

ABHISHIKTA DEY, MATTHEW J.S. PARKER

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Abstract

This rare group of autoimmune diseases characteristically presents as painless, progressive proximal muscle weakness with a raised creatine kinase level but can also manifest in many other ways. It is important for GPs to recognise them because, without prompt treatment, a patient’s condition can rapidly deteriorate, resulting in permanent organ damage or death.

Key Points

  • The idiopathic inflammatory myopathies (IIMs) include polymyositis, dermatomyositis, inclusion body myositis and a growing number of other subtypes.
  • The IIMs are individually rare but serious chronic conditions that can affect patients at any age and have substantial associated morbidity and mortality.
  • The characteristic clinical presentation is painless, progressive proximal muscle weakness and a raised creatine kinase level.
  • The differential diagnosis of weakness and/or a raised creatine kinase level is extensive, and specialist referral is warranted once more common conditions, such as endocrine disorders or drug-related causes, are excluded.
  • The IIMs can cause a broad range of extramuscular organ manifestations, such as rash, interstitial lung disease, symptoms of Raynaud’s syndrome, dysphagia and arthritis.
  • A careful clinical assessment is central to making a diagnosis but diagnostic tools, such as novel autoantibody tests, are improving.
  • There are no treatment guidelines, but most patients with IIMs will receive corticosteroids and an additional immunosuppressive agent.
  • GPs are ideally placed to assist with many aspects of the patient’s management, such as monitoring blood pressure, weight gain, bone density loss and blood glucose and lipid levels and ensuring all recommended cancer screening is up to date.

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