Erythema Nodosum — Tender Red Shin Nodules

A 28-year-old woman presents with tender, warm, erythematous nodules on the anterior shins bilaterally that appeared over the past 2 weeks. She reports fever, arthralgias, and recent sore throat treated with antibiotics. On examination, the lesions are 2–3 cm, non-ulcerating, and non-scarring. Skin biopsy confirms the diagnosis. The underlying pathology marked **D** in the diagram—reactive septal panniculitis—indicates that erythema nodosum is fundamentally a hypersensitivity reaction. Which of the following is the MOST important next step in management of this patient?