A 45-year-old man is evaluated for recurrent urolithiasis. He underwent a Roux-en-Y procedure for morbid obesity two years ago. He passed his first kidney stone one year ago and has passed several since then. He has lost approximately 15 kg (33 lb) since the surgery and feels well otherwise. His current medications include lisinopril for hypertension, esomeprazole for gastro-esophageal reflux disease, and a daily multivitamin. He has no family history of kidney stones.
Which of the following factors is most likely responsible for this patient's kidney stone formation?

Question

A 45-year-old man is evaluated for recurrent urolithiasis.  He underwent a Roux-en-Y procedure for morbid obesity two years ago.  He passed his first kidney stone one year ago and has passed several since then.  He has lost approximately 15 kg (33 lb) since the surgery and feels well otherwise.  His current medications include lisinopril for hypertension, esomeprazole for gastro-esophageal reflux disease, and a daily multivitamin.  He has no family history of kidney stones.
Which of the following factors is most likely responsible for this patient's kidney stone formation?

Quizplus · Accepted Answer

11ec193a_9902_fcff_853d_6d3f4c50dcfa_MD0002_00 This bariatric surgery patient has recurrent urolithiasis that is likely due to calcium oxalate stones caused by hyperoxaluria and hypocitraturia. Calcium oxalate stones commonly occur in patients with malabsorption due to small bowel disease (e.g., Crohn's disease), bowel resection with intestinal bypass (e.g., bariatric surgery), and cystic fibrosis. Malabsorption causes more intestinal fatty acid binding to calcium, which increases colonic oxalate absorption and renal oxalate excretion. Malabsorption also causes low urinary citrate due to unclear reasons. One possibility is hypokalemia or chronic metabolic acidosis (from malabsorptive diarrhea), leading to increased citrate reabsorption in the renal proximal tubules. Since citrate is an inhibitor of kidney stones, the combined effect of hyperoxaluria and hypocitraturia increases the risk of kidney stones by up to 4% per year. Patients can be treated with a low oxalate diet and exogenous citrate supplementation. (Choice B) Hypercalciuria is most commonly associated with calcium stones seen in primary hyperparathyroidism and chronic metabolic acidosis. However, it is not a significant contributor to malabsorption-associated kidney stone formation. (Choice C) Hyperuricosuria and low urine pH are known risk factors for uric acid stones; however, they are not associated with calcium oxalate stones due to malabsorption. (Choice D) Patients with bowel disorders and significant diarrhea can have low urinary volumes, which by itself is not a significant risk factor for calcium oxalate stones. Low urinary volume can contribute to uric acid and calcium oxalate stones when combined with low urine pH, metabolic acidosis, and hypocitraturia. (Choice E) The Roux-en-Y procedure can lead to decreased absorption of fat-soluble vitamins (e.g., vitamin D), but vitamin D excess (not deficiency) is associated with calcium stones. Educational objective: Recurrent urolithiasis commonly occurs in gastric bypass patients due to hyperoxaluria and hypocitraturia. Treatment involves a low oxalate diet and exogenous citrate supplementation. __________ References: Effect of gastric bypass surgery on kidney stone disease. (http://www.ncbi.nlm.nih.gov/pubmed/19375090) Hyperoxaluria in kidney stone formers treated with modern bariatric surgery. (http://www.ncbi.nlm.nih.gov/pubmed/17222634)

A 45-Year-Old Man Is Evaluated for Recurrent Urolithiasis