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Pathology
Polymyositis is an idiopathic inflammatory myopathy, which is an immune-mediated condition secondary to defective cellular immunity
Dermatomyositis is muscle + skin involvement
Aetiology
Primary or secondary to rheumatic disease or malignancy
Signs
Dermatomyositis - Heliotrope rash, Periorbital oedema, Gottron’s papules: red,
scaly lesions on dorsum of hands and Shawl sign: erythematous rash over back and shoulders
Symptoms
Symmetrical, progressive proximal muscle weakness (difficulty standing from sitting, climbing stairs), dysphagia, myalgia, shortness of breath
Investigations
Bloods: FBC, Raised CRP, CK and ESR
Auto-antibodies: ANA, Anti-Jo1, Rheumatoid Factor
Urine: Myoglobinuria
Imaging: Electromyography (EMG) shows fibrillation potentials
Treatment
Medical: Corticosteroids, immunosuppression, intravenous immunoglobulin
Prognosis
Poor prognostic factors include advanced age, female, systemic disease, associated malignancy
Interstitial lung disease, aspiration pneumonia, heart block arrhythmias and malabsorption
Key Facts
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Key Images
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Key References
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