A primary case presentation of nephrolithiasis from enteric hyperoxaluria due to Crohn's disease.

Learning objective was to recognize colonic oxalate absorption resulting in hyperoxaluria and nephrolithiasis as a long-term metabolic complication of small bowel resection. A 53-year-old man with a history of Crohn's disease presented with progressive fatigue, oliguria, and watery diarrhea over a 2-week period. He had undergone extensive ileal resection 25 years ago for Crohn's disease. Laboratory testing revealed acute renal failure, hyperkalemia, metabolic acidosis and severe pancytopenia. Urinalysis did not reveal crystalline deposits; 24-hour urine studies demonstrated hyperoxaluria, hypocalciuria, hypocitraturia and hypomagnesuria. X-rays revealed multiple bilateral ureteral calculi and a renal ultrasound showed hydronephrosis. He underwent bilateral ureteral stent placement after which his renal failure dramatically improved. We concluded that the patient had enteric hyperoxaluria due to excess oxalate absorption in his colon leading to subsequent excretion in his urine. The hyperoxaluria served as a nidus for calcium oxalate nephrolithiasis then obstructive uropathy. Dietary restrictions for oxalate, calcium, and fats were advised, and cholestyramine with appropriate mineral supplements was prescribed. Enteric hyperoxaluria can complicate small bowel resection in the presence of an intact colon, and is associated with calcium oxalate nephrolithiasis. In the intact intestine, dietary oxalate binds to calcium, forming insoluble calcium oxalate and is not absorbed. In Crohn's disease fat malabsorption occurs, allowing calcium to bind to fatty acids, leaving oxalate unbound for passage to the colon where it gets both absorbed and excreted. This results in hyperoxaluria and oxalate nephropathy. Diagnostic features include a low urinary pH, low urinary volumes, hyperoxaluria, hypocalciuria and hypocitraturia. Medical treatment includes dietary oxalate and fat restriction along with cholestyramine, calcium and citrate supplementation. In severe recurrent cases, an ileostomy may be indicated.

Farida Millwala, MD, and Samuel Cykert, MD. Moses H. Cone Memorial Hospital, Department of Internal Medicine, Greensboro, NC.