Kidney Stones and Children
Five-year-old Alex Williamson of Savage, Minn., returns to his elementary school after undergoing a series of tests and medical examinations at Children's Hospital in Minneapolis. He is eager to get back to his kindergarten class. "I have knee stones," he reports to the school secretary.
That's kidney stones, honey," laughs Danielle Williamson, Alex's mother.
The secretary looks confused. "How could it possibly be kidney stones?" she asks.
A Growing Concern
One of the most common disorders of the urinary tract in adults, kidney stones are increasingly common in children's urinary tracts, much to the surprise of many parents.
"Kidney stones occur because of a variety of factors, including defined metabolic and genetic disorders and exposure to medication and other environmental influences, including geographic location and socioeconomic level," says Dr. John C. Pope IV, physician and assistant professor of urologic surgery and pediatrics at Vanderbilt Children's Hospital in Nashville, Tenn.
Vanderbilt Children's Hospital recently opened a pediatric kidney stone clinic to provide services for children affected by kidney stones. Tennessee lies in what doctors describe as the "kidney stone belt": Kentucky, Tennessee, Virginia, North Carolina and Georgia.
Not Just Hereditary
Dr. Yuri Reinberg, pediatric urologist at Pediatric Surgical Associates in Minnesota, says the majority of children with stones have some type of metabolic anomaly – an irregularity in the way the body processes certain minerals. "Ninety-two percent of these [cases] are calcium-related anomalies," says Dr. Reinberg. "Most common are calcium phosphate supersaturation and calcium oxalate supersaturation."
Calcium phosphate stones contain calcium and phosphate, while calcium oxalate stones contain calcium in combination with oxalate. These chemicals are present in every body as part of a normal diet. Urine contains certain chemicals that inhibit these minerals from binding together and forming crystals; however, these inhibitors don't work for everyone.
The less common types of stones include struvite stones that are associated with bacterial urinary infections; cystine stones, caused by excessive cystine in the urine; and uric acid stones, caused by excessive uric acid in the urine. Calcium phosphate, calcium oxalate, struvite, cystine and uric acid stones all can be hereditary.
Other causes can be related to diet or medication. "Too much salt [sodium] in the diet can cause elevations in urine calcium, which can lead to stones," says Dr. Pope. "The major offender, however, is probably the lack of adequate hydration in the diet. Certain medications can also cause increased calcium excretion in the urine that leads to stone formation, such as furosemide, which is often given to premature infants."
What Is a Kidney Stone?
Kidney stones form when substances in the urine crystallize. These crystals bond together to form a mass in the center of the kidney where urine collects before passing through the ureter. Small stones can easily slip through the ureter and pass out of the body through the urine virtually undetected. Larger stones can irritate the ureter as they pass, often causing pain and possibly blocking the flow of urine. Even larger stones, too large to pass through the ureter, can become lodged in the kidney, requiring surgical intervention to remove.
A variety of procedures are available to a child diagnosed with kidney stones, depending on the size and location of the stone. The first method is observation – waiting for the stone to pass out of the body in the urine on its own. This method, also called spontaneous passage, is recommended for smaller stones. Medications are often used to ease the pain, and the patient is asked to drink lots of water to help move the stone through the ureter.
Extracorporeal shock wave lithotripsy (SWL) is a procedure used to break apart larger stones, enabling the smaller fragments to pass easily through the ureter. A lithotripter makes shock waves that travel through the body, creating stress on the stone. The doctor uses ultrasound to focus the waves on the stone inside the patient's body until the stone eventually crumbles. Following this procedure, a stent is often inserted through the urethra and bladder and into the ureter, assisting the fragments to pass through the ureter.
Ureteroscopy (URS) involves inserting a ureteroscope up the urethra, through the bladder and into the ureter, allowing the doctor to view the stone. Ureteroscopes contain channels that allow the doctor to insert various devices through the channels to remove or fragment the stone. A stent is left in the ureter for a few days following the procedure to aid in healing.
When stones become lodged in the upper ureter, percutaneous nephrolithotomy (PNL) is often performed. PNL involves making a small incision in the flank area of the skin. A thin guide wire is inserted through the incision, into the kidney and down the ureter with the aid of X-rays to allow the doctor to guide the wire. Dilators are inserted to stretch the tissue, creating a passageway that allows the doctor to view the stone, break the stone using sound waves and then remove the stone fragments. A small tube into the kidney is left in place for a few days to aid in a second PNL, if necessary.
Maintaining Kidney Health
"Recurrent stones are almost five times as likely in children who have an identifiable metabolic abnormality," says Dr. Pope. "These children have close to a 50 percent recurrence rate." Once stones are identified, steps should be taken to reduce the chance of recurrence. Dr. Pope recommends lots of water, salt in moderation and good medical follow-up.
Diet plays a key role in the maintenance of stone-free kidneys. Depending on the stone type, a variety of dietary restrictions must be maintained to control the situation. "Interestingly, many parents give their children sports drinks with the thought that this will increase their fluid intake," says Dr. Pope. "These drinks, however, contain lots of sodium, and as such, can be counterproductive. Red meat (i.e. high intake of protein) also causes increased urine levels of oxalate, calcium and uric acid, other major components of some stone diseases."
For children diagnosed with the most common types of stone, a diet low in sodium is essential. Despite the fact that these stones contain calcium, this essential nutrient cannot be limited in the diet of growing children and should be consumed regularly to promote good growth.
"Kidney stones are a very frustrating problem for both parents and children. It often requires multiple surgical procedures as well as lifelong medication to prevent stone recurrence," says Dr. Pope. "A good relationship between the families and treating physicians is imperative."