Necrotizing Fasciitis Extending from the Left Iliopsoas to the Left Thigh Due to Retroperitoneal Penetration of the Descending Colon: A Case Report.

INTRODUCTION: Necrotizing fasciitis is a severe soft tissue infection characterized by rapid destruction of the fascia and subcutaneous tissue, with a high mortality rate of 20%-40%. Although trauma and insect bites are common causes, gastrointestinal perforation as an etiology is exceedingly rare.

CASE PRESENTATION: We report the case of a 70-year-old man receiving combination immunotherapy with nivolumab and ipilimumab for malignant pleural mesothelioma. The patient had been taking 12.5 mg of prednisolone daily for 6 months to manage immunotherapy-induced adrenal insufficiency and enteritis. He presented with lower abdominal pain and chills and was diagnosed with septic shock upon hospital arrival. CT revealed extensive gas extending from the left abdominal wall to the retroperitoneum and left thigh, confirming necrotizing fasciitis. Emergency surgery revealed feculent fluid near the left iliopsoas muscle, indicating retroperitoneal perforation of the descending colon. The patient underwent a left hemicolectomy and double-barrel ileostomy, followed by multiple surgical debridement and drainage procedures. After infection control, he recovered and was transferred for rehabilitation.

CONCLUSIONS: Immunosuppressed patients receiving prolonged steroid therapy may be at a higher risk of developing necrotizing fasciitis due to gastrointestinal perforation. Timely infection control and aggressive surgical management are essential for improving patient outcomes.