Dermatomyositis: Dermatomyositis: an inflammatory myopathy with characteristic skin signs (heliotrope rash, Gottron's papules, shawl sign); idiopathic or paraneoplastic. and Management

Key points

• Dermatomyositis: an inflammatory myopathy with characteristic skin signs (heliotrope rash, Gottron's papules, shawl sign); idiopathic or paraneoplastic.
• Investigations: raised creatine kinase; EMG and muscle biopsy (perifascicular inflammation); muscle MRI.
• Autoantibodies: ANA positive in about 60%; anti-Mi-2 highly specific but seen in only ~25%; anti-Jo-1 associates with antisynthetase syndrome (ILD, arthritis).
• Screen for underlying malignancy (ovary, lung, breast, GI) - dermatomyositis is often paraneoplastic, especially in older adults.
• Management: high-dose corticosteroids first-line with a steroid-sparing immunosuppressant (azathioprine, methotrexate, mycophenolate); IV immunoglobulin or rituximab for refractory disease.