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

  • Hypokalemia
  • Hypophosphatemia
  • Thyroid disorder (hypothyroidism or hyperthyroidism)
  • Myopathies
  • Inclusion body myositis
  • Drug Induced myopathies (EtOH, antimalarials, colchicine, antifungals)

Weakness

Diagnosis

  • CBC, ESR, CRP, CK, UA, RF, ANA, Anti-Jo-1

Management

  • Prednisone 1mg/kg/day for 4-8 weeks until CK returns to reference range
  • Followed by prednisone taper
  • Methotrexate as second line for poor response to corticosteroids
  • Other agents with less evidence: IVIG, TNF Inhibitors

Disposition

  • Rheumatology or neurology consultation either in ED or as outpatient depending on severity of symptoms
  • Very strongly associated with malignancy (~30%), especially:[1]
    • Ovarian
    • Lung
    • Pancreatic
    • Stomach
    • Colorectal
    • Lymphoma
    • Bladder

References

Tintinalli

  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.