Postoperative Pyoderma Gangrenosum Mimicking Early Periprosthetic Joint Infection After Total Hip Arthroplasty in a Patient With Hairy Cell Leukemia: A Diagnostic Challenge.

Pyoderma gangrenosum (PG) is a rare, sterile neutrophilic dermatosis characterized by rapidly progressive, painful cutaneous ulcerations and frequently associated with systemic diseases, including inflammatory bowel disease, rheumatologic disorders, and hematologic malignancies. In particular, recognition of PG as a cutaneous manifestation of an underlying hematologic neoplasm can be critical for timely diagnosis of the systemic disease. Postoperative PG after total hip arthroplasty may closely mimic early periprosthetic joint infection and can lead to unnecessary surgical revisions and prolonged antibiotic therapy.  An 83-year-old woman underwent elective right total hip arthroplasty for end-stage osteoarthritis. Her history included arterial hypertension and mild leukocytopenia; the left hip arthroplasty 10 years earlier had been uncomplicated. The index procedure and early postoperative course were initially uneventful. On postoperative day 6, erythema developed around the wound, followed by pustule formation, purulent-hemorrhagic secretion, and a secondary rise in C-reactive protein (CRP). Early periprosthetic joint infection was suspected, and the patient underwent two revision surgeries with extensive debridement, head and liner exchange, and broad-spectrum antibiotics. Intraoperatively, inflammation remained confined to skin and subcutaneous tissue without fascial or muscular involvement, and microbiological cultures were largely negative or yielded organisms interpreted as contaminants. Dermatologic consultation and histopathologic examination ultimately confirmed PG. Negative-pressure wound therapy was discontinued, topical wound management was continued, and systemic corticosteroids were initiated after early granulation tissue formation, resulting in gradual local improvement and secondary wound healing. Given the known association between PG and hematologic malignancies, a targeted hematologic work-up was performed and subsequently revealed an underlying hairy cell leukemia, providing a unifying explanation for the patient's chronic leukocytopenia. Postoperative PG after elective total hip arthroplasty is a diagnostic challenge that may be misinterpreted as early periprosthetic joint infection. Atypical wound deterioration with severe pain, superficial distribution of inflammation, negative cultures, and pathergy after surgical interventions should raise suspicion of PG and prompt dermatologic and histopathologic evaluation. In addition, clinicians should be aware of the strong association between PG and hematologic malignancies and pursue appropriate hematologic assessment when clinically indicated. Early recognition and timely immunosuppressive treatment are crucial to avoid repeated surgical trauma and to facilitate prompt identification and management of associated systemic diseases such as hairy cell leukemia.