[Nephrolithiasis in patients with intestinal diseases]

Intestinal diseases may cause the formation of urinary stones through changes in the metabolism of oxalate, calcium, and uric acid. The oxalate that is excreted into urine comes from the catabolism of ascorbic acid and some amino acids or from intestinal absorption of food oxalate. Calcium is absorbed by the gut after the stimulation of active vitamin D and is excreted by the kidney under the control of the bone/parathyroid hormone axis. Uric acid is generated by the oxidation of exogenous and endogenous purine bases, is excreted by the kidney through glomerular filtration/tubular secretion, and is soluble in alkaline urine. Several data indicate that patients with inflammatory bowel diseases are at high risk of urinary stones containing calcium-oxalate salt or uric acid. Calcium-oxalate stones are caused by colonic oxalate hyperabsorption (secondary to intestinal dysfunction) or by parenteral nutrition. Uric acid stones are typical of patients with severe diarrhea and/or intestinal neostomy, that is, in patients with hyperconcentrated acidic urine. Relationships between malabsorptive intestinal diseases and urinary stones are less well defined. Preventive countermeasures are not the same for all disorders. Hyperoxaluria should be controlled by diets with a low content of lipids and oxalate but supplemented with calcium and probiotics. The presence of hyperconcentrated acidic urine should be controlled by correct hydration and administration of citrate.