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A 71-year-old woman with a history of intermittent generalized pruritus of unclear etiology and right knee osteoarthritis underwent total knee arthroplasty. She presented 8 weeks postoperatively with a 1-week history of scattered pruritic bullae around her incision site. She reported that the symptoms were unlike any rashes she had had before. She had no fever, knee pain, or lower extremity swelling. She was taking no medications and had no allergies.
On examination, she was afebrile and well-appearing. Knee examination showed no effusion and normal range of motion without pain. Her incision was fully healed. Several 1- to 2-cm tense, fluid-filled bullae were present around the incision. There was no surrounding erythema or edema.
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B. Perform skin biopsy with direct immunofluorescence study
The key to the correct diagnosis was the pattern of tense bullae with clear exudate and associated severe pruritus, typical for bullous pemphigoid. Recognizing bullous pemphigoid features helps avoid unnecessary antimicrobial treatment and diagnostic interventions. Biopsy with direct immunofluorescence (DIF) revealed a linear pattern of IgG along the dermal-epidermal junction, consistent with the diagnosis of bullous pemphigoid.1 Aspiration of the knee to investigate for prosthetic joint infection (choice A) is not indicated in this case, as the patient had no symptoms concerning for an intra-articular infection, such as pain or warmth. A diagnosis of allergic and irritant contact dermatitis (ACD) may be confirmed with skin patch testing (choice C); however, in this patient, the bullae were larger than would be expected for ACD, and symptoms would have appeared earlier in the postoperative course and should have resolved with oral corticosteroids. Further antibiotic treatment for bullous impetigo (choice D) would not be indicated for this patient, as the clinical appearance was not consistent with impetigo (lack of honey-crusted lesions) and there was no improvement with either topical iodine or oral cephalexin.
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Corresponding Author: Christopher J. Fang, MD, Department of Orthopedic Surgery, New England Baptist Hospital, 125 Parker Hill Ave, Boston, MA 02120 (firstname.lastname@example.org).
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient and the patient’s family for providing permission to share the patient’s information. We also thank Thea Miller, BS (New England Baptist Hospital), for helping with collection and coordination of patient data and with preparation of the initial manuscript and James V. Bono, MD (New England Baptist Hospital), the operative surgeon. Neither received any compensation for their contributions.
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