Dual Urolithiasis in an Older Infant with Left-Sided Duplicated Collecting System: A Rare Association of Ammonium Urate and Brushite

Abstract

Introduction: Pediatric urolithiasis is an increasingly prevalent condition worldwide, with a multifactorial etiology that includes metabolic abnormalities, congenital urinary tract anomalies, urinary tract infections, and environmental factors; among its less frequent forms are brushite stones, characterized by aggressive behavior and high recurrence rates, and ammonium urate stones, typically associated with infections; Case presentation: We report the case of a 13-month-old female infant with a urinary tract infection caused by Proteus vulgaris with an extended-spectrum beta-lactamase (ESBL) phenotype, associated with bilateral renal lithiasis with stones measuring up to 9.6 × 8 mm, left duplicated collecting system, and bilateral calyceal dilation; Metabolic evaluation and stone composition: Metabolic assessment revealed hypocitraturia, hyperuricosuria, and vitamin D deficiency, without abnormalities in phosphorus absorption, and spectroscopic analysis demonstrated an unusual stone composition consisting of 50% brushite (calcium monohydrogen phosphate) and 50% ammonium urate; Treatment and outcome: The patient required two surgical interventions with endoscopic ureterolithotomy and bilateral double-J catheter placement, in addition to medical management with oral sodium citrate at a dose of 2 mEq/kg/day, nutritional intervention, and follow-up by medical genetics; Conclusions: This case highlights the interaction between anatomical anomalies, urinary tract infections caused by urease-positive bacteria, and metabolic disturbances in the pathogenesis of pediatric urolithiasis, underscoring the need for a multidisciplinary and individualized approach to prevent recurrence and preserve long-term renal function.