A 62-Year-Old Man Comes to the Emergency Department Because of Right-Sided

A 62-year-old man comes to the emergency department because of right-sided back pain, nausea, and dark urine. He reports alternating episodes of decreased urine output followed by a temporary increase in urine output for the past 2 days. In the past year, he has had two urinary tract infections. He has Crohn disease and underwent a small bowel resection 5 years ago. He currently takes mesalamine and a multivitamin. His father had recurrent kidney stones. His vital signs are within normal limits. X-ray of the abdomen reveals a nonspecific bowel gas pattern with no evidence of renal calculi.  Ultrasound of the abdomen shows a 4-mm stone in the distal right ureter.  The patient is treated with analgesics and the stone passes spontaneously.  Microscopic analysis of the stone reveals a pure uric acid stone.  Which of the following is the most likely underlying mechanism leading to stone formation in this patient?

A) Bile salt malabsorption in the ileum
B) Concentrated acidic urine
C) Increased uric acid production
D) Infection with urea-splitting bacteria
E) Overproduction of parathyroid hormone

Correct Answer:

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