Pathogenesis of nephrolithiasis post-partial ileal bypass surgery: case-control study. The POSCH Group

Calcium oxalate crystal related kidney injury in a patient receiving Roux-en Y hepaticojejunostomy due to gall bladder cancer

Background

Calcium oxalate nephropathy is rare in current practice. It was a common complication during jejunoileal bypass, but much less seen in modern gastric bypass surgery for morbid obesity. The major cause of it is enteric hyperoxaluria.

Case presentation

We report on a patient here with acute kidney disease due to calcium oxalate nephropathy, rather than the conditions mentioned above. The male patient received a Roux-en Y hepaticojejunostomy and common bile duct drainage. In addition to enteric hyperoxaluria, chronic kidney disease related metabolic acidosis, chronic diarrhea related volume depletion, a high oxalate and low potassium diet, long term ascorbic acid intake and long term exposure to antibiotics, all predisposed him to having oxalate nephropathy.

Conclusion

This is the first case with such conditions and we recommend that similarly diagnosed patients avoid all these predisposing factors, in order to avoid this rare disease and its undesired outcome.

Epidemiology and clinical pathophysiology of uric acid kidney stones

There is global diversity in the prevalence of uric acid (UA) nephrolithiasis. UA nephrolithiasis comprises 8-10 % of all kidney stones in the United States. However, its prevalence is higher in patients with type 2 diabetes mellitus and those with obesity. Three significant urinary abnormalities have been described as the main etiologic factors for the development of UA nephrolithiasis; low urinary pH, hyperuricosuria and low urinary volume. However, an unduly acidic urine below the ionization constant of uric acid (pKa < 5.5) increases the urinary content of undissociated uric acid and thereby uric acid precipitation. Previous studies have shown the two major pathogenic mechanisms for unduly urinary pH are increased net acid excretion (NAE) and reduced renal ammonium (NH4 (+)), with a combination resulting in overly acidic urine. The impaired ammonium excretion has been demonstrated in a steady state in 24-hour urine and also following an oral ammonium chloride (NH4Cl) challenge to amplify ammoniogenic defects in this population. Similar abnormalities have been disclosed in normal populations and also in T2DM populations without kidney stones. To date, the underlying mechanism of increased acid production, source and nature of putative organic acid anions have not been fully elucidated. One plausible mechanism is the production of organic acid by intestinal and aerobic metabolism. This may occur in obese, diabetic and uric acid stone formers due to the differences in gut microflora.

Short bowel syndrome

The short bowel syndrome (SBS) is a state of malabsorption following intestinal resection where there is less than 200 cm of intestinal length. The management of short bowel syndrome can be challenging and is best managed by a specialised multidisciplinary team. A good understanding of the pathophysiological consequences of resection of different portions of the small intestine is necessary to anticipate and prevent, where possible, consequences of SBS. Nutrient absorption and fluid and electrolyte management in the initial stages are critical to stabilisation of the patient and to facilitate the process of adaptation. Pharmacological adjuncts to promote adaptation are in the early stages of development. Primary restoration of bowel continuity, if possible, is the principle mode of surgical treatment. Surgical procedures to increase the surface area of the small intestine or improve its function may be of benefit in experienced hands, particularly in the paediatric population. Intestinal transplant is indicated at present for patients who have failed to tolerate long-term parenteral nutrition but with increasing experience, there may be a potentially expanded role for its use in the future.

Nephrolithiasis and nephrocalcinosis in rats with small bowel resection

Intestinal resection (IR) may lead to hyperoxaluria and nephrolithiasis. A rat model of IR was developed, in which kidney stones form. We describe the urine chemistries and histopathologic features. Rats underwent resection of 40-45 cm of distal ileum (n=16) or sham resection (SR) (n=8), and were then fed a 1% Na oxalate, 0.02% Ca diet. After 1 week on the diet, 24 h urine samples were obtained for stone chemistries. At 4-7 months after surgery, kidneys were examined grossly and by light microscopy. The extent and location of crystallization was assessed by polarized light. Histochemistry and infrared spectroscopy were used to determine crystal composition. IR rats had higher urine oxalate excretion (P<0.01) and concentration (P<0.001) than SR rats, and lower urine citrate excretion; only IR rats formed kidney stones (12/15 surviving rats). Tissue calcification was found only in kidneys from IR rats, located in the cortex (83% of kidneys), medulla (73%) and papillary tip (47%). Crystals, composed of CaOx, apatite, and calcium carbonate, filled collecting duct lumens, and were associated with tubular obstruction, and interstitial inflammation. Crystals in the papillary interstitium incited inflammation with tubular destruction and development of progressive papillary erosion. This new rat model of nephrolithiasis and nephrocalcinosis resembles the pattern of urinary abnormalities and tissue calcification that may be seen in humans with small bowel resection. The model allows further studies of the mechanisms of renal crystal formation, and possible therapeutic interventions.

Urine stone risk factors in nephrolithiasis patients with and without bowel disease

BACKGROUND

The prevalence of nephrolithiasis among patients with bowel disease is higher than in the general population. We examined urine stone risk factors and clinical characteristics of these patients, contrasted with a large group of stone forming patients without systemic disease.

METHODS

A total of 180 patients with bowel disease were compared with a group of 2048 nephrolithiasis patients with calcium or uric acid stones and without systemic diseases. Bowel diseases included inflammatory bowel disease with and without bowel resections, bowel resections from cancer or trauma, and bypass procedures for obesity or hypercholesterolemia. Urine stone risk factors, stone rates, stone compositions, and creatinine clearance were measured.

RESULTS

Compared to ordinary stone forming patients, bowel patients formed stones higher in rate of recurrence and in uric acid content. Uric acid content was highest when colon surgery had occurred. Urine volumes were low among all bowel patients except those with a bypass. Average creatinine clearance values were low among all bowel patients. Urine oxalate excretion was modestly elevated after small bowel resection, but very high with bypass. Supersaturations were increased mainly by low urine volume and-for uric acid-low pH. Patients with no surgery were indistinguishable from routine stone formers.

CONCLUSIONS

Low urine volume and pH are the main stone-forming abnormalities in bowel disease patients. Hyperoxaluria is extreme after bypass, but only modest after small bowel surgery. In the absence of surgery, bowel disease patients with stones cannot be distinguished from common stone formers by comprehensive stone risk measurements.

Stones from bowel disease

Kidney stones are increased in patients with bowel disease, particularly those who have had resection of part of their gastrointestinal tract. These stones are usually CaOx, but there is a marked increase in the tendency to form uric acid stones, as well, particularly in patients with colon resection. These patients all share a tendency to chronic volume contraction due to loss of water and salt in diarrheal stool, which leads to decreased urine volumes. They also have decreased absorption, and therefore diminished urinary excretion, of citrate and magnesium, which normally act as inhibitors of CaOx crystallization. Patients with colon resection and ileostomy form uric acid stones, as loss of bicarbonate in the ileostomy effluent leads to formation of an acid urine. This, coupled with low urine volume, decreases the solubility of uric acid, causing crystallization and stone formation. Prevention of stones requires treatment with alkalinizing agents to raise urine pH to about 6.5, and attempts to increase urine volume, which increases the solubility of uric acid and prevents crystallization. Patients with small bowel resection may develop steatorrhea; if the colon is present, they are at risk of hyperoxaluria due to increased permeability of the colon to oxalate in the presence of fatty acids, and increased concentrations of free oxalate in the bowel lumen due to fatty acid binding of luminal calcium. EH leads to supersaturation of urine with respect to CaOx, in conjunction with low volume, hypocitraturia and hypomagnesuria. Therapy involves a low-fat, low-oxalate diet, attempts to increase urine volume, and agents such as calcium given to bind oxalate in the gut lumen. Correction of hypocitraturia and hypomagnesuria are also helpful.

Metabolic risk factors for stone formation in patients with cystic fibrosis

PURPOSE

Cystic fibrosis is characterized by chronic pulmonary disease, insufficient pancreatic and digestive function, and abnormal sweat concentrations. Patients with cystic fibrosis also have an increased incidence of nephrolithiasis. We compared the results of metabolic evaluation in patients with cystic fibrosis with and without nephrolithiasis.

MATERIALS AND METHODS

A total of 496 patients were evaluated at our center, including 98 with a mean age of 25 years who had cystic fibrosis and complete metabolic evaluation available between 1996 and 2000. Of these patients 13 (13%) had a history of nephrolithiasis. The records were reviewed for clinical characteristics and all patients underwent metabolic evaluation, including serum electrolyte measurement and 24-hour urine collection. Statistical analysis was done to compare the stone versus nonstone groups.

RESULTS

The incidence of nephrolithiasis in our study was 3%. We identified 13 patients 16 to 41 years old (mean age 27) with nephrolithiasis, of whom 62% had had multiple episodes. Flank pain was the presenting symptom in 9 of the 13 cases (69%). Renal ultrasound and computerized tomography were the most common imaging modalities. In 9 cases stones were passed without intervention, extracorporeal shock wave lithotripsy was required in 2 and ureteroscopy with stone extraction was done in 2. Calcium oxalate was the dominant stone composition in the 9 patients in whom stone analysis was performed. Metabolic evaluation of the stone versus no stone groups showed elevated urinary oxalate (45.5 versus 42.5 mg./24 hours), relative calcium oxalate supersaturation (5.3 versus 7.2) and decreased urinary citrate in the 2 groups. There was a statistical difference in citrate excretion with lower levels in stone formers (102 versus 218 mg./24 hours, p = 0.0007).

CONCLUSIONS

Patients with cystic fibrosis have an increased incidence of nephrolithiasis and are at high risk for recurrence. Metabolic evaluation is indicated in all patients with cystic fibrosis and urolithiasis since most have hyperoxaluria, urinary calcium oxalate supersaturation and decreased urinary citrate. Correcting detected stone risk factors in these cases may decrease stone recurrence.