Miss A presented at 13 months of age with obstructive urosepsis secondary to a 10 mm diameter calculus at the left Pelviureteric Junction (PUJ). She had three days of fever and vomiting, continuing despite 48 hours of oral co-trimoxazole commenced in the community for presumed UTI.

Miss A’s medical and surgical history, growth and developmental milestones were normal. Immunisations were up to date. She is a Caucasian New Zealander born to non-consanguineous parents with no family history of nephrolithiasis.

Initial examination findings of note included temperature of 38.6^○C, mild tachycardia (130 bpm) and tachypnoea (Respiratory rate 36 breaths/min). Laboratory tests confirmed raised inflammatory markers and normal renal function. The first urine sample cultured Citrobacter freundii as the predominant organism in a mixed growth.

A urinary tract ultrasound performed on day two showed a dilated left upper pole calyx with echogenic debris, reduced perfusion of the left kidney and associated pyelonephritis. Repeat ultrasound performed three days later for persistent fevers confirmed persistent left calyceal dilatation worst at the upper pole, echogenic debris and a 10-millimetre calculus at the left PUJ [Figures 1a-c]. Right urinary tract was unremarkable.

After transfer to a tertiary surgical centre, she underwent ultrasound guided insertion of left nephrostomy tube. The turbid urine from nephrostomy grew citrobacter freundii, sensitive to both gentamicin and co-trimoxazole.

A nephrostogram performed five days later showed multiple left intra-renal calculi and obstructing ureteric calculi, so she proceeded to open left pyelolithotomy. Intra-operative findings confirmed inflamed left renal parenchyma with multiple fibrinous adhesions to peri-nephric tissue, multiple small calculi measuring up to five millimetres with debris in all poles, intra-parenchymal calcification and a dilated proximal left ureter. Nephroscopy was used to facilitate stone clearance. Stones removed were sent for analysis [Figure 2]. Clearance of all intrarenal stones was confirmed on nephroscopy and intra-operative ultrasound. A left nephrostomy tube, Double J ureteric stent and an indwelling urethral catheter were placed. Follow up ultrasound performed five days later showed a new non-obstructing 2.6 mm intrarenal stone in the right midpole, while two small stones remained in the left upper pole calyx with mild residual dilatation.

Anitibiotic therapy continued throughout, and oral potassium citrate was started while metabolic investigations were completed. Staged removals of the urethral catheter, nephrostomy tube and ureteric stent were all successful during the 10 weeks following surgery.

As IR spectroscopy was unavailable in the local laboratory, stone composition was initially reported as urate (LTA Kidney Stone Analysis Kit, Milano, Italy). This kit uses a wet chemical analysis technique: a technique known to have an inability to differentiate between urate and 2,8-dihydroxyadenine [1,2]. Metabolic analysis of 24-hour urine collection confirmed raised urinary adenine 0.074 mmol/L (normal range: 0.000-0.001), and urinary 2,8-dihydroxyadenine of 0.254 mmol/L (normal range: 0.000-0.001). The original urinary tract stones were sent to a laboratory with Fourier Transform Infrared Spectroscopy (FTIR) and these confirmed stones were 60% 2,8-DHA, 20% uric acid and 20% unknown.  All other serum and urinary biochemical investigations were unremarkable.

Definitive treatment with allopurinol, low protein diet and increased oral fluid intake was started and potassium citrate discontinued. Expert advice was obtained from the Great Ormond Street Children's Hospital (United Kingdom), Mayo clinic (United States of America) and National University Hospital of Iceland.

Miss A is now 3 years old and has been registered with The Rare Kidney Stone Consortium Patient Registry [3]. She continues on lifelong allopurinol and completed a one-year course of prophylactic co-trimoxazole. Long-term dietary plans include purine restriction and targeted oral fluid intake (1.5 L/m^{2 BSA}). Her surveillance investigations for nephrolithiasis include six-monthly urinary tract ultrasound with paired urine (2, 8- DHA/Creatinine ratio, microscopy and albuminuria) and blood tests (renal function). Post-operative DMSA renogram was normal. She has not required any further surgery for urolithiasis, but has passed several calculi spontaneously. Her most recent surveillance ultrasound in June 2019 has shown a stable 6 mm non-obstructing left lower pole renal stone, with adequate interval growth of both kidneys.