Dermatomyositis — Heliotrope Rash and Gottron Papules

A 48-year-old woman presents with 3 months of progressive proximal muscle weakness and a distinctive photosensitive rash. Examination reveals violaceous erythema and edema of the upper eyelids, and erythematous papules overlying the metacarpophalangeal and interphalangeal joints, as shown in the diagram marked **A**. Laboratory studies show creatine kinase 4,200 U/L (>10× normal), and myositis-specific autoantibodies are positive for anti-TIF1-gamma. Given this autoantibody profile and clinical presentation, what is the most appropriate next step in management?