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