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Kidney Stones
 

Kidney Stones Introduction

The medical term for kidney stones is nephrolithiasis. [1] The actual stone is referred to as a calculus or calculi (plural). There are many different types of calculi, however the majority (75%) are composed of calcium. [2] Kidney stones can occur in any place along the urinary tract and lead to symptomatic pain, also known as renal colic. Depending on the type of stone, the specific pathogenesis may vary. For example, a uric acid stone is the result of increased urine acidity which crystallizes undissociated uric acid, while magnesium ammonium phosphate calculi indicate a urinary tract infection caused by a specific type of bacteria. [1] However, a common feature is that the urine contains a high amount of specific salts that allow stones to form. As well, patients often have abnormalities of crystal growth inhibitors (pyrophosphate, citrate, and glycosaminoglycans) and preformed nuclei for the stones to form. [1, 2] It can be said that a variety of factors must be present for calculi to form. Patients can have urine saturated with the aforementioned salts, but not result in stone formation.

The types of kidney stones can be divided into four main categories: calcium-containing stones, triple or struvite stones (magnesium ammonium phospahate), uric acid stones and cystine stones. [2] Calcium containing stones, as mentioned above, account for the vast majority of cases. Most of these stones are made up of calcium oxalate and are due to increased calcium in the urine. Fifty percent of these patients have idiopathic hypercalcuria, which refers to an abnormally high amount of calcium in the urine. [2] This condition is hereditary, and far more common in women.

Hyperoxaluria, or high oxalates in the urine, is responsible for about five percent, of calcium oxalate stones. [2] This is largely due to disorders of the digestive tract, which allow excess oxalate absorption, or by consuming massive amounts of oxalate containing foods such as rhubarb, spinach, or nuts. A few of these patients have a primary/underlying disorder that directly leads to hyperoxaluria.

Kidney Stones Symptoms

Patients with kidney stones generally present pain in the mid to low back, which can be due to a blockage in the renal system caused by a kidney stone. [1] This pain has a particular pattern and is referred to as renal colic. The lining of the ureter (the tube that connects the kidney to the bladder) is irritated causing increased frequency and force of peristaltic movement of urine, which results in the colicky pain seen in these patients. [4] Typically, a patient will experience episodes of intermittent extreme pain across the flank region, which may extend across the abdomen. Depending on where the stone has lodged, there may be pain very low in the abdomen, or just above the pubic bone if a stone has reached the bladder.

Blood in the urine (hematuria) can be a sign of kidney stones. Other symptoms include nausea, vomiting, distention of the abdomen, chills, fever, and polyuria (frequent urination). A patient can also appear very agitated due to the colicky pattern of pain.

Kidney Stones Statistics

  • Approximately 1 in 1000 Americans present in hospital due to kidney stones. [1]
  • The incidence of nephrolithiasis is increasing in the Western world and is proposed to be a disease of lifestyle, just like heart disease.
  • Kidney stones occur more commonly in males, and the National Institutes of Health cite that 80% of cases are seen in the male population. [2]

Kidney Stones Treatment

Treatment of kidney stones is divided into two categories: prophylaxis (preventative) and immediate treatment. Patients presenting with a kidney stone could receive narcotics for the pain or possibly shock wave lithotripsy if they are; very symptomatic, have a stone less than 2 cm in diameter, and if it is in the pelvis of the kidney or in the ureter. [5] There are also a variety of medical procedures, such as endoscopy, that may be percutaneous (from above) or ureteroscopic (from below). The only stones that can possibly be dissolved chemically are uric acid stones via prolonged alkalinization of the urine.

Once a person has passed a stone or experienced removal, they should be treated preventatively (prophylaxis) because there is a high rate of recurrence. Depending on the type of metabolic abnormality the treatment approaches will vary. [5] For example, patients with hypercalciuria will be prescribed thiazide diuretics which decrease the amount of calcium going out in the urine, as well as lower the amount of calcium oxalate. This results in a greatly decreased rate of stone formation. Patients with uric acid stones caused by hyperuricosuria can take allopurinol to lower uric acid production. They may also be prescribed alkalinizing drugs, like potassium citrate, and be advised to increase water intake. In the case of struvite stones, the associated urinary tract infection from urea-splitting bacteria will be treated using antibiotic therapy.

Supplements helpful for Kidney Stones

Calcium

Paradoxically, calcium supplementation actually decreases levels of calcium in the urine of most patients. [6, 7] This is thought to be due to the formation of calcium oxalate complexes in the GI tract that are poorly absorbed. It has been shown that calcium taken with food is protective, but when taken away from food, it can be problematic. [8, 9, 10] Therefore, when taking calcium supplements, they must be taken with food if the goal is to reduce calcium oxalate stone formation.

Vitamin B6

Pyridoxine is also known as vitamin B6. There is a large body of evidence supporting the use of this vitamin for prophylactic treatment of kidney stones. Many years ago, a deficiency of pyridoxine was documented to be associated with calcium oxalate stone formation. [11] Since then, many studies have examined the various treatment approaches concerning patients with recurrent calcium oxalate stones. [12, 13, 14]

Patients with idiopathic calcium oxalate stones and mixed calcium oxalate/calcium phosphate stones received vitamin B6 supplementation for 4.5 to 6 years. [9] These patients showed a significant decrease in stone formation without major side effects. Vitamin B6 is also useful in the treatment of patients who have the metabolic disorder, primary hyperoxaluria, which can cause nephrolithiais. [15, 16, 17]

Magnesium

Magnesium supplementation has been observed to have profound effects on patients with recurrent kidney stone formation. [18, 19, 20] It appears that magnesium increases the solubility of calcium oxalate, thereby decreasing the incidence of stone formation. One study demonstrated that 85% of patients in the magnesium treatment group were stone free during the four year treatment period. [18] The form of magnesium used in these studies was magnesium hydroxide.

Citrate

Citrate is an important nutritional supplement to consider for the prevention of kidney stones. It has been shown to be very effective against calcium oxalate calculus formation. [21] A beneficial feature of citrate is that it can be taken as a form of other nutrients such as calcium citrate or magnesium citrate.

References

1. Merck Manual of Diagnosis. Merck Research Laboratories, Whitehouse Station, NY, 1999: 1838-1839.

2. Robbins et al. Pocket Guide to Robbins Pathologic Basis of Disease, 6th Ed. WB Saunders Company, Philadelphia, PA 1999;493.

3. NIH Consensus Conference. Prevention and Treatment of Kidney Stones. JAMA 1988;260:977-981.

4. Handbook of Signs and Symptoms. Springhouse Corp, Spirnghouse, PA, 1998:62.

5. Merck Manual of Diagnosis. Merck Research Laboratories, Whitehouse Station, NY, 1999: 1840.

6. Curhan GC et al A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. New Engl J Med 1993;328:833-838.

7. Curhan GC et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk of kidney stones in women. Ann Intern Med 1997;126:497-504.

8. Goldfarb S. Dietary factors in the pathogenesis and prophylaxis of calcium nephrolithiais. Kidney Int 1988;34:544-555.

9. Curhan GC et al. A prospective study of the intake of Vitamins C and B6 and the risk of kidney stones in men. J urol 1996;155:1847-1851.

10. Levine et al. Effect of calcium citrate supplementation on urinary calcium oxalate saturation in female stone formers: Implications for prevention of osteoporosis. Am J Clin Nutr 1994;60:592-596.

11. Lyon ES et al. Calcium oxalate lithiasis produced by pyridoxine deficiency and inhibition with high magnesium diets. 1966;4:133.

12. Prien EL and Gurshoff SN. Magnesium oxide-pyridoxine therapy for recurrent calcium oxalate calculi. J Urol 1974;112:509-512

13. Thind SK et al. Role of Vitamin B6 in oxalate metabolism in urolithiais. Am J Clin Nutr 1979;32(6):xx(Abstract).

14. Murthy MSR et al. Effect of pyridoxine supplementation on recurrent stone formers. Int J Clin Pharmacol Ther Toxicol 1982;20:434.

15. Will EJ and Bijvoet OLM. Primary oxalosis: clinical and biochemical response to high dose pyridoxine therapy. Metabolism 1979;28:542.

16. Yendt ER and Cohanim M. Response to a physiologic dose of pyridoxine in primary hyperoxaluria (PH) Type 1. Urol Res 1984;12:27.

17. Milliner DS et al. Results of long-term treatment with orthophosphate and pyridoxine in patients with primary hyperoxaluria. N Engl J Med 1994;331:1553-1558.

18. Johansson G et al. Biochemical and clinical effects of the prophylactic treatment of renal calcium stones with magnesium hydroxide. J Urol 1980;124:770.

19. Johansson G et al. Effects of magnesium hydroxide in renal stone disease. J Am Coll Nutr 1982;1:179-185.

20. Rattan V et al. Effect of combined supplementation of magnesium oxide and pyridoxine in calcium oxalate stone formers. Urol Res 1994;22:161-165.

21. Harvey et al. Calcium citrate: Reduced propensity for the crystallization of calcium oxalate in urine resulting form induced hypercalciuria of calcium supplementation. J Endocrin Metab 1985;61:1223-1225.