To Kill the Calyces: A Rare Case of Xanthogranulomatous Pyelonephritis Complicated by Emphysematous Pyelonephritis

Xanthogranulomatous pyelonephritis (XPN) is a rare chronic renal infection associated with obstructive nephrolithiasis and recurrent urinary tract infections. Emphysematous pyelonephritis (EPN) is an even rarer necrotizing infection characterized by intrarenal gas, most commonly seen in patients with uncontrolled diabetes mellitus. Concurrent presentation of XPN and EPN is exceedingly uncommon, with only a few cases reported. We present a case of a 61-year-old female with no history of diabetes who presented with left flank pain, systemic symptoms, and laboratory evidence of infection and microcytic anemia. Abdominal CT revealed imaging features consistent with XPN-including hydronephrosis, a staghorn calculus, and the classic "bear paw" sign-alongside intrarenal gas, consistent with EPN. Urine culture grew Proteus mirabilis. The patient underwent nephrectomy and recovered uneventfully with antimicrobial therapy. This case is notable for the rare co-occurrence of XPN and EPN in a euglycemic patient, supporting the hypothesis that chronic obstruction and infection may be sufficient to induce gas-forming infections, even in the absence of hyperglycemia. Awareness of atypical presentations is essential, as early recognition and surgical management are critical to reducing morbidity in these severe renal infections.