A Rare Case of Emphysematous Pyelonephritis Following Retrograde Intrarenal Surgery in an Elderly Man.

BACKGROUND Emphysematous pyelonephritis (EPN) is a severe, rare urinary tract infection (UTI) primarily affecting patients with diabetes or compromised immune function. Characterized by nonspecific manifestations including fever, flank pain, and pyuria, it frequently overlaps with other renal or abdominal conditions, leading to diagnostic delays and increased mortality risk. Notably, EPN following retrograde intrarenal surgery (RIRS) - a minimally invasive technique for renal and ureteral stone management - is extremely rare, with no prior documented cases in the literature. CASE REPORT A 74-year-old Chinese man was admitted on May 15, 2024 due to a >3-cm right ureteropelvic junction stone, multiple right renal stones, and concurrent right renal hydronephrosis. Preoperative urine culture identified Klebsiella aerogenes and Citrobacter koseri, prompting 9 days of perioperative levofloxacin (500 mg/day), which cleared the infection. Despite guideline recommendations for percutaneous nephrolithotomy, he opted for RIRS, undergoing first-stage surgery with double-J catheter placement on May 24 and discharging uneventfully on May 27. On postoperative day 10 (June 3), he developed a 39°C fever and persistent abdominal pain. CT confirmed Grade 1 EPN, ureteral steinstrasse, and persistent hydronephrosis. Urgent percutaneous nephrostomy, catheter replacement, and 11-day ertapenem therapy (1g/day) controlled the infection, and a second RIRS on June 12 cleared the stones, with no complications in 3-month follow-up. CONCLUSIONS Post-RIRS fever/abdominal pain requires urgent imaging to rule out steinstrasse-induced EPN. Early drainage, targeted antibiotics, and staged RIRS are critical for elderly patients with high stone burden, filling the literature gap on this complication.