You are correct. Biopsy of the shin nodules was consistent with erythema nodosum, and the patient met the criteria for Behcet disease, given her recurrent oral ulcerations plus genital ulcerations, erythema nodosum, and pathergy (she developed a red pustule at a venipuncture site).

Arthritis affects the medium and large joints (e.g., wrists, hips, knees, ankles) in approximately half of patients with Behcet disease. The cause is still unknown, but HSV, streptococcus, and gene sensitivity of the human leucocyte antigen B51 serotype are believed to be contributing factors.

The patient was treated with methylprednisolone. The fever, skin lesions, and arthritis subsided within a week. Azathioprine was given daily for 6 months, and the steroid dose was tapered gradually and discontinued after 3 months. She reported no ulcerations or skin lesions at a follow-up visit 6 months later.

BMJ 2021;374:n1956