Polymyositis

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

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

References

Tintinalli