Ammonium acid urate stone due to laxative abuse: a case report

We report a case of ammonium acid urate stone due to laxative abuse. A 27-year-old female complained of left flank pain. Computed tomography revealed bilateral ureter stones (right 16.5 x 9.0 mm; left 4 mm), while left ureter stone was radiolucent on the plain X ray film. Bilateral hydronephrosis was seen, but no therapy was performed for the right stone, because 99mTc-MAG3 scintigraphy revealed that right kidney had no function. The left stone was successfully removed by transurethral approach. The stone was revealed to be an ammonium acid urate by infrared spectrophotometry. She had been taking many laxatives (bisacodyl, sennoside, aloe extract) for 12 years to control her body weight. Ammonium acid urate stones are rarely seen in developed countries. We have reviewed 9 cases in Japan, describing ammonium acid urate stones due to laxative abuse. Among these patients, 24-hour urine volume and excretion in urinary sodium were decreased, and serum aldosterone was increased. The involvement of laxative abuse should be considered when ammonium acid urate is formed in a woman with a low body mass index.