A woman in her 70s presented with a 2-year history of a persistently itchy erythematous plaque involving the perianal skin. Previous empirical treatments with topical glucocorticoids, antibiotics, and antifungals had been ineffective. Physical examination revealed an indurated moist, erythematous plaque with superficial erosion, focal white scale, and surrounding hyperpigmentation located circumferentially around the anus and extending anteriorly to involve the perineum (Figure 1). No other lesions or extracutaneous symptoms were observed. Digital rectal examination and inguinal lymph node palpation were unremarkable, and fungal culture findings were negative.

A skin biopsy was obtained that revealed an intraepidermal infiltration of large atypical cells with ample cytoplasm consistent with Pagetoid cells (Figure 2). Immunohistochemical staining was positive for CK7 and GCDFP15 in atypical cells and negative for CK20, carcinoembryonic antigen, HMB45, and p63. Further evaluation, including thoracoabdominal computed tomography, pelvic magnetic resonance imaging, and rectal endoscopy, showed no abnormalities. The patient was diagnosed with perianal Paget disease (PPD) and a wide local excision was performed ensuring negative resection margins. No recurrence or metastasis was observed during the 2-year follow-up period.