A 70-year-old woman complained of pain in the right lower abdomen in the region of her allograft. She received a decease-donor renal transplant eight years previously. Her native kidney disease was due to diabetes and other medical diagnoses, including hypertension and peripheral vascular disease. Her medications included acarbose, amlodipine, famotidine, lovastatin, liraglutide, metoprolol, prednisone, and tacrolimus. On examination, she was afebrile. She did have tenderness to palpation in the right lower quadrant and over the area of her allograft.
Her white blood cell count was 6,200. The creatinine level was at her baseline of 1.5 mg/dL. Calcium was 8.4 mg/dL, sodium was 134 mEq/, potassium was 4 mEq/L, CO2 was 24 mEq/L. Urinalysis showed specific gravity of 1.012, pH 6.5, over 180 red blood cells, and 50 white blood cells.
Two different imaging modalities demonstrate nephrolithiasis and representative images are shown. She was treated for presumptive pyelonephritis and eventually underwent urologic procedure for relief of stone burden. Chemical analysis of stones revealed magnesium phosphate.
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The clinical data including results of stone analysis are consistent with a diagnosis of struvite stones. Struvite stones are composed of magnesium ammonium phosphate and calcium carbonate and precipitate in alkaline urine. Urine infections with urease-splitting organisms lead to stone formation. Implicated organisms include Proteus and Klebisella to name a few.
Complete stone removal and eradication of bacteria are necessary for successful treatment and prevention of recurrence. Percutaneous nephrolithotomy is generally the stone removal method of choice. It may be done in tandem with shockwave lithotripsy. Shockwave lithotripsy alone with urinary stent can be considered in those with smaller stones and appropriate anatomy.
Older studies have suggested that urease inhibitors, such as acetohydroxamic acid, can limit stone growth in patients with struvite stones. Its side effect profile may limit its use. Allopurinol can be considered in those who are hyperuricosuric or have uric acid stones. Hydrochlorothiazide is useful in patients who are hypercalciuric. Mercaptopropionyl glycine may be considered in those suffering with cysteine stones.
Answer: Acetohydroxamic acid
This case was provided by Kevin Harley, M.D., Assistant Clinical Professor of Medicine at the University of California in Irvine.
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