KIDNEY STONES
Kidney stones afflict 5% of the population. Twice as many men as women have stones. Men are most likely to have a stone in their early 30’s and women are more likely to have them between ages 35 to 55. Once a stone has forms, the likelihood that a second stone will form within 5 to 7 years is about 50%.
Stones are either calcium containing and visible on x-rays or non-calcium stones that are not visible on x-rays. About 75% of stones are calcium oxalate or calcium phosphate. Urine volume and concentration of the mineral components of the stone within the urine are the main factors that lead to stone formation. Risk factors for stone formation include a positive family history (increases risk by three), insulin resistance, high blood pressure, hyperparathyroidism (a disorder of a gland that regulates calcium balance in the body), gout, metabolic acidosis and surgical menopause. Abnormal anatomy of the kidney or ureter (tube that drains from the kidney to the bladder) is another risk factor. Metabolic abnormalities that promote stone formation include high urinary excretion of calcium, uric acid, oxalate or citrate. Drugs that may increase stone formation include the diuretic triamterene, certain seizure medications, decongestants and indinavir.
Clinical signs of a kidney stone include pain in the kidney or groin, blood in the urine, painful urination and difficulty passing urine. The pain is often intermittent and can be severe. Nausea and vomiting may occur and infection with fever and chills may sometimes complicate the problem.
Treatment depends on the size of the stone, the location and whether the anatomy of the urinary system is normal or not. Uncomplicated stones can be managed conservatively with good fluid intake and pain medications. Active heat application to the kidney and lower abdomen is helpful for the pain and nausea. Recent studies show that anti-inflammatory medication is more effective than narcotics for pain relief. Over 90% of stones in the ureter (this is where the severe pain occurs) will pass spontaneously if less than 5 millimeters in diameter. Only 50% of stones 5 to 10 millimeters in diameter will pass without intervention. Interventions to remove stones include surgery, shock wave lithotripsy (breaking up the stone by focused ultrasound waves) and passing instruments through the bladder into the ureter to extract the stone.
Formation of new stones can be prevented by increasing fluid intake to 2-3 liters of fluid daily, reducing intake of animal protein below 2 ounces daily, restricting salt intake, eating adequate calcium, decreasing dietary oxalate (in spinach, nuts, rhubarb and chocolate) and drinking cranberry juice. If there measures are not successful and attacks occur often, more complicated measures can be taken after determining the composition of the stone and the concentration of the stone constituents in the urine.
Daniel Blodgett MD