Clinical Decision-Making and Multidisciplinary Management of Peristomal Pyoderma Gangrenosum in Stage IVB Rectal Cancer: A Case Report—Corticosteroid Response but Fatal Cancer Progression

Background and Clinical Significance: Peristomal pyoderma gangrenosum (PPG) is a rare subtype of pyoderma gangrenosum, most commonly associated with inflammatory bowel disease or haematologic disorders. Its occurrence in patients with solid malignancies is uncommon. PPG in an oncologic setting poses diagnostic and therapeutic challenges because systemic immunosuppressive therapy, wound care, and ongoing chemotherapy must be carefully balanced; Case Presentation: We report the case of a Japanese man in his 50s with stage IVB rectal adenocarcinoma who developed rapidly progressive peristomal ulceration clinically consistent with PPG around a colostomy 12 weeks after initiation of panitumumab-containing systemic chemotherapy. The diagnosis was made on clinical grounds and was strongly supported by the clinical morphology, exclusion of major mimickers, and response to systemic corticosteroid therapy, although histopathological confirmation was not obtained. Because existing diagnostic criteria for pyoderma gangrenosum are not specifically designed for peristomal disease, they were used as supportive rather than definitive diagnostic tools. Skin biopsy was avoided due to the risk of pathergy at the peristomal site. Superficial cultures were not obtained because frequent cleansing and faecal contamination were likely to compromise diagnostic accuracy. To minimise mechanical pathergy, the stoma appliance was changed from a one-piece soft convex system to a two-piece flat system. Multidisciplinary management, including systemic corticosteroids, meticulous stoma care, and selective ultrasonic debridement, resulted in complete epithelialisation by Week 26. Chemotherapy was temporarily withheld during the active inflammatory phase and later resumed. Despite successful control of the peristomal ulceration, the patient died from progressive malignancy at Week 34; Conclusions: This case highlights the clinical challenge of balancing immunosuppressive therapy for clinically suspected PPG with ongoing oncologic treatment. Mechanical pathergy related to stoma appliance use was considered a more likely precipitating factor than chemotherapy alone, although panitumumab may have contributed to impaired cutaneous repair. Close collaboration among dermatologists, oncologists, surgeons, WOC nurses, and family caregivers is essential for multidisciplinary decision-making in complex oncologic settings.