A 71-year-old woman presented 8 weeks after total knee arthroplasty with a 1-week history of scattered tense, pruritic bullae around the incision site but no surrounding erythema or edema. She was afebrile and had no known allergies; the pruritus and bullae remained unchanged after a course of oral cephalexin and prednisone. What is the diagnosis and what would you do next?
