Extensive Scalp Angioedema Following High-Dose Diphenylcyclopropenone for Alopecia Areata

In 2014, a 31-year-old Caucasian male developed extensive angioedema of the head and neck 10 days after using a 2% diphenylcyclopropenone solution topically on his scalp to treat alopecia areata. The patient experienced edema, acute inflammatory changes, scalp erythema, and serous fluid drainage. He was treated with intravenous steroids and antihistamines during hospitalization, followed by oral steroids and antihistamines as an outpatient. The reaction to diphenylcyclopropenone was deemed probable with a Naranjo score of 8. Although not FDA-approved, diphenylcyclopropenone is used to induce allergic contact dermatitis to treat alopecia areata, typically starting at a high concentration and then reducing for weekly applications. The patient had applied the 2% concentration on multiple consecutive days, which likely contributed to the adverse reaction. The study concluded that frequent use of high-concentration diphenylcyclopropenone can cause scalp angioedema.