Kidney Stone Theory

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Most kidney stones can be left untreated, according to guidelines recently issued by the American Urological Association, and doctors should stop treating these painful calcium crystals with a technique called blind basket extraction. This is one of several high-tech interventions introduced over the last 20 years to break up, snare, or disintegrate kidney stones.

Joseph W. Segura, M.D., and colleagues who served on the guidelines panel conducted a computerized search of all relevant studies to determine which stones require intervention and which treatments have the best outcome. According to the panels guidelines, published in this months issue of Urology, 98% of small stones (less than half a centimeter) can be safely allowed to pass through the body without any treatment. In many cases, people have symptomless kidney stones diagnosed incidentally during a test for another purpose. Usually, these silent stones can be left alone, except when they start to move down the ureters, the tubes connecting the kidneys to the bladder. The pain caused by this movement can be agonizing. Drinking plenty of water and taking painkillers will aid in the passage of a stone through the ureter. The panels first choice of treatment for slightly larger stones (one centimeter or less) lodged near the kidneys is a technique called extracorporeal shock-wave lithotripsy.This is a non-surgical procedure which pulverizes the stones with ultrasound administered outside the body.

Lithotripsy and ureteroscopy are appropriate treatments for larger stones lodged near the bladder, according to the new guidelines. For ureteroscopy, a fiberoptic instrument fitted with a tiny camera is threaded through the bladder and ureter using fluoroscopy (motion x-rays) as guidance. Viewing their work on a TV screen, the doctors remove the stone with a basket-shaped instrument or dissolving it with a laser. Studies showed that both lithotripsy and ureteroscopy had similar outcomes. Lithotripsy is less invasive than ureteroscopy, but the former has a 20-30% failure rate versus the nearly 100% success rate of the latter.

Unfortunately, there are no head-to-head comparisons of treatments for kidney stones. Because kidney stones differ in size, location, and composition, there have been no controlled clinical trials in which people are randomly assigned to one of several treatment methods. This was noted by Dr. Segura and colleagues as a limitation to the process of developing treatment guidelines.

The new guidelines advise doctors to reserve the most drastic treatment, open surgery, for the uncommon circumstance of a large kidney stone or one caught in an unusual place such as the entrance to the ureter. Dr. Segura and colleagues advised against use of blind basket extraction because its done without fluoroscopic guidance and thus presents the most risks, specifically damaging the ureter and leaving stone fragments behind. Blind basket extraction represents an estimated 5% of all treatment currently administered to people with kidney stones.

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By Maryann Napoli

PREVENTION
Men are twice as likely as women to develop kidney stones. Once a person develops a stone, he or she has a 50% higher chance of spawning another within the next five to seven years. Until four years ago, when a study proved it erroneous, the standard prevention advice was restriction of dietary calcium intake. (About 75% of kidney stones are composed of calcium oxalate.) Gary C. Curhan, M.D., and colleagues at the Harvard School of Public Health followed over 45,000 men with no history of kidney stones and found that high dietary calcium intake actually decreases the risk of stones (New England Journal of Medicine, 25 March 1993). A similar and more recent study, conducted by the same Harvard team, followed over 91,000 women and found an important distinction between dietary calcium and calcium supplements. High consumption of calcium-rich food appeared to decrease the rate of kidney stones, but taking calcium supplements may increase the risk (Annals of Internal Medicine, 1 April 1997).

Gout, the use of calcium-based antacids, and excessive intake of vitamin D and salt are all associated with a higher than normal risk of developing kidney stones. On the other hand, drinking plenty of water (about two quarts daily) and long-term use of thiazine diuretics, usually prescribed for hypertension or edema, can prevent the development of kidney stones.

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