Dermatomyositis and polymyositis

• Gradual symmetric proximal weakness; DM: heliotrope eyelid rash, Gottron's papules over knuckles, elbows and knees, photosensitive rash; ILD, arthralgia, Raynaud's, dysphagia; increased cancer risk (DM).

• Investigations: CK, AST/ALT, ANA, myositis antibodies (anti-Jo-1, Mi-2, SRP, PL-7), EMG, muscle biopsy, chest CT, age-appropriate cancer screening.

Management

• Physiotherapy.

• A: Prednisone (PO) 0.5–1 mg/kg/day, tapered as the patient improves (first-line).

• Steroid-sparing: S: methotrexate 10–25 mg weekly, OR S: azathioprine 1.5–2.5 mg/kg daily, OR S: hydroxychloroquine 200–400 mg daily (skin disease), OR S: cyclophosphamide 500–1000 mg/m² IV every 4 weeks.

• Severe or refractory: IV immunoglobulin; S: rituximab IV 1000 mg × 2 doses 2 weeks apart.

• Monitor strength, CK and rash; watch for ILD and malignancy.