Violaceous Nodules on the Leg of an Alemtuzumab-Treated Kidney Transplant Recipient: Challenge

CLINICAL HISTORY A 43-year-old woman with end-stage renal disease secondary to autosomal dominant polycystic kidney disease, on peritoneal dialysis since 2020, underwent a deceased-donor kidney transplant in September 2024. Induction immunosuppression consisted of alemtuzumab, followed by maintenance tacrolimus, mycophenolate mofetil, and prednisolone. Early after transplantation, she developed a class I donor-specific anti-Human leukocyte antigens (HLA) antibody with a biopsy showing changes suspicious for antibody-mediated rejection and was treated with 7 sessions of plasma exchange and intravenous immunoglobulin in addition to high-dose corticosteroids and optimization of mycophenolate. Her medical history also included type 2 diabetes mellitus and hypertension. In January 2025, approximately 4 months after transplantation, she presented with a 4-week history of painful nodules on the medial aspect of the right lower leg. The lesions had progressively enlarged and coalesced into a violaceous, crusted plaque with focal ulceration (Fig. 1). She denied fevers, weight loss, or other systemic symptoms. Multiple courses of oral antibiotics prescribed in primary care for a presumed bacterial skin infection had not resulted in improvement. Examination revealed several firm, tender, violaceous nodules and an irregular ulcerated plaque on the medial lower leg; there was no palpable lymphadenopathy and no other cutaneous lesions.FIGURE 1.: Multiple tender, violaceous nodules coalescing into an ulcerated plaque on the medial lower leg of a kidney-transplant recipient.HISTOPATHOLOGIC FINDINGS A 4-mm punch biopsy from the edge of a nodule showed a lobulated endophytic squamoproliferative lesion with parakeratosis, neutrophilic microabscesses, and mild cytologic atypia, raising concern for keratoacanthoma or well-differentiated squamous cell carcinoma in the setting of recent renal transplantation. Because of the multifocal, tumor-like appearance, a larger incisional biopsy was performed to further characterize the process (Fig. 2).FIGURE 2.: Histopathology of the incisional biopsy. A, Low-power hematoxylin–eosin–stained section showing irregular pseudoepitheliomatous epidermal hyperplasia with broad lobulated squamous downgrowths overlying a dense nodular dermal inflammatory infiltrate. B, Medium-power view highlighting tongues of bland squamous epithelium extending into the dermis, surrounded by a mixed inflammatory infiltrate. C, High-power view showing neutrophil-rich microabscesses and “dirty” necrotic debris between collagen bundles adjacent to reactive squamous epithelium with only mild atypia.WHAT IS YOUR DIAGNOSIS? (Continued on page 250)