Polymyositis

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Background

  • Idiopathic inflammatory myopathy causing symmetric proximal muscle weakness, elevated CK, and characteristic EMG findings

Clinical Features

  • Symmetrical proximal muscle weakness with insidious onset
  • Generally painless (though 30% have myalgia)
  • Difficulty with kneeling, climbing stairs, combing hair, or rising from a seated position
  • Weak neck extensors causing difficulty of holding head up
  • Associated arthralgias

Differential Diagnosis

Myalgia

Weakness

Evaluation

Workup

  • CBC
  • ESR
  • CRP
  • CK: Most sensitive muscle enzyme
  • Urinalysis
  • Consider:
    • LDH
    • AST/ALT
    • Aldolase
    • RF
    • ANA
    • Anti-Jo-1
    • Myositis antibody panel

Diagnosis

  • Typically requires muscle biopsy

Management

  • Prednisone 1mg/kg/day for 4-8 weeks until CK returns to reference range
  • Other treatments that rheum may prescribe:
    • Methotrexate as second line for poor response to corticosteroids
    • Other agents with less evidence: IVIG, TNF Inhibitors
  • Assess for interstitial lung disease
    • CXR, consider CT chest
    • Pulmonary function tests (PFTs)
  • Screen for associated malignancy, especially:[1]
    • Ovarian
    • Lung
    • Pancreatic
    • Stomach
    • Colorectal
    • Lymphoma
    • Bladder

Disposition

  • Rheumatology or neurology consultation either in ED or as outpatient depending on severity of symptoms

See Also

References

  1. Hill CL et al. Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study. Lancet. 2001 Jan 13;357(9250):96-100.