A Rare Case of Xanthogranulomatous Pyelonephritis

Introduction: Xanthogranulomatous pyelonephritis (XPN) is a rare variant of chronic pyelonephritis occurring in the setting of obstructive uropathy and recurrent urinary tract infections (UTIs). It accounts for less than 1% of all cases of pyelonephritis. Diabetes is a known systemic risk factor. Localized symptoms such as flank pain and dysuria may be attributed to nephrolithiasis or UTI without prompting a need for further workup. We present a case of XPN which resulted in kidney loss and dialysis dependence. Case Description: A 54-year-old Hispanic female with a history of HTN, type 2 DM, kidney stones and recurrent UTIs presented with two years duration of intermittent right flank pain that acutely worsened one week prior to hospital admission. Most recent antibiotic use was one month prior. On physical exam patient appeared clinically stable, blood work was notable for a creatinine of 1.26 mg/dL, WBC of 11k/uL, and a urine culture growing Proteus Mirabilis. Renal ultrasound showed a 4 cm stone chronically obstructing the right ureteropelvic junction. CT scan demonstrated right-sided staghorn calculus with perinephric inflammation and a pathognomonic bear paw sign. Patient subsequently underwent right-sided nephrectomy. Postoperative hospital course was complicated by hemorrhagic shock, IVC thrombus, and persistent kidney failure. Patient remained dialysis dependent. Discussion: XPN is a difficult diagnosis given that there are no specific symptoms until late stage. Exact etiology remains largely unknown. Malek et al proposed a three-stage classification of XPN, with stage II or diffuse type being the most common type and characterized by destruction of renal parenchyma (higher attenuation on CT) and dilated calyces (lower attenuation), mimicking a bear's paw. Our case highlights the importance of high clinical suspicion of XPN in diabetic patients with recurrent UTIs and kidney stones. Perinephric inflammatory changes are known predictors of poor outcomes. Early clinical and radiologic suspicion along with awareness of risk factors play an important role in preventing disease progression and avoiding late-stage complications including ESRD.Bear paw sign