Inflammatory Myopathy (Polymyositis / Dermatomyositis)

Pathophysiology

Overview

Inflammatory myopathies are rare autoimmune conditions causing progressive proximal muscle weakness and pain, with dermatomyositis additionally presenting with characteristic skin changes. They require urgent rheumatological investigation and are not managed conservatively as a primary approach.

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Medically Managed — Refer Early

This condition is primarily medically managed. Osteopathic care may play a supportive role — refer early if suspected.

Typical Presentation

Site

Proximal limb girdle — shoulder and hip girdles predominantly

Quality

Aching weakness more than pain; difficulty raising arms or climbing stairs

Intensity

Progressive over weeks to months; often underestimated early

Aggravating

Sustained activity, progressive over weeks to months

Relieving

Immunosuppressive treatment (medical management)

Associated

Elevated CK, skin rash (heliotrope rash, Gottron's papules in DM), dysphagia, constitutional symptoms

⚠ Red Flags

  • •Progressive proximal weakness with elevated CK — urgent rheumatology referral
  • •Dysphagia or respiratory muscle involvement suggesting systemic progression
  • •Heliotrope rash or Gottron's papules suggesting dermatomyositis
  • •Associated interstitial lung disease or cardiac involvement

⚡ Yellow Flags

  • •Delayed diagnosis due to presenting as general myalgia or fatigue
  • •Patient avoiding referral due to fear of serious diagnosis

Referral Criteria

  • •Urgent rheumatology referral — this condition is not appropriate for primary conservative management
  • •GP referral for CK, ANA, anti-Jo-1 antibody panel, and EMG/muscle biopsy workup
  • •Oncology if paraneoplastic myopathy suspected (particularly in older patients)