While kidney stones are still relatively uncommon in children, the number of cases is growing. In response, Children's Hospital Boston has established the
Pediatric Kidney Stone Center to care for children with kidney stones, those who've previously had them and those who are
at risk for developing them. Here, the center's co-directors discuss why kidney stones are becoming more common in children and how metabolic evaluation can help prevent them.
How many patients are seen in the clinic?
Dr. Nelson: A few years ago, we'd see a new patient about once a month. Now it seems like we see new cases every week.
To what do you attribute the increase?
Dr. Nelson: There may be a number of reasons. Children are getting less physical activity, which is contributing to an
increased incidence of obesity. Diet is also a factor, as many children get too much salt, eat highly processed foods and don't drink enough water. Stones form when there's too much of the stone-forming
material and not enough water in the urine, so dehydration is a major contributor. It's too early to say that diet is the chief
culprit, but it's a leading candidate.
Improved methods of diagnosing stones may also be a reason for the increase.
At what age do children usually form kidney stones?
Dr. Nelson: They can form at any age but we generally see school-aged children and older. There's also a subset of patients who are much younger. These are premature babies whose medications throw off the balance of minerals in their urine and lead to kidney stone formation.
What is the most common type of stone?
Dr. Nelson: Most children have some
variety of calcium stones. A significant
minority have other types, such as uric acid stones or stones resulting from one of several rare inherited disorders. As in adults, the stones can be lodged in the kidney or in the ureter.
What are typical symptoms?
Dr. Cilento: Symptoms may vary from none, in the case of "silent stones," to
excruciating pain due to urinary
obstruction. Most obstructing stones cause pain, nausea and vomiting. In older children, flank or back pain is typical. In younger children, symptoms may be vague and the child may not be able to pinpoint the location of the pain. For all children, blood in the urine is a key tip-off, and any child with pain accompanied by blood in the urine, either microscopic or gross, should be evaluated.
Are certain children predisposed to
forming kidney stones?
Dr. Cilento: Any child who has had
previous kidney stones, has a urologic disease or had urologic surgery is at risk. Basically, any condition that results in
obstruction or stasis of urine, or that
results in abnormal drainage of urine puts them at increased risk. Many cases we see are children with urologic conditions,
but most are not. Children with prolonged immobilization may also be susceptible because when bones are inactive, they're unable to regenerate themselves
properly, which results in calcium being flushed into the system. There's also a
genetic factor.
Dr. Baum: There's also a correlation
between patients who suffer from
malabsorption problems and the
formation of kidney stones, so children with cystic fibrosis or gastrointestinal
disorders may be at increased risk.
Do environmental conditions affect
stone formation?
Dr. Cilento: In New England, we see more cases in the summer and fall when children tend to be more active, sweat more and are more prone to dehydration.
Dr. Baum: The highest concentration of Americans with kidney stones come from what we refer to as the "Stone Belt" in the southeastern states. This is probably due to the warm weather in those states that can cause mild dehydration.
What types of treatment do you offer?
Dr. Cilento: Treatment is determined based on the size, location, number and
composition of the stone(s). In many cases, they can be passed spontaneously without any surgical treatment, since children can pass stones that are relatively large, compared with adults. Other times, it's necessary to remove them, usually
using extracorporeal shock wave
lithotripsy (ESWL), percutaneous
nephrolithotomy, ureteroscopy or open stone surgery. The most common
treatment is ESWL, which uses a
lithotripter to send shock waves through the skin into the body and fragment the stone. It's the least invasive treatment.
Dr. Baum: We also do a metabolic
evaluation and take a urine sample to
assess for factors that contribute to stone
formation, such as increased levels of
calcium. We perform blood tests to look for other risk factors. Once the stone is passed or removed, we perform a
chemical analysis to identify its type.
This can provide important clues about why it formed.
What's the best way to prevent recurrence?
Dr. Baum: It depends upon the type of stone and identifying risk factors. We
prescribe individualized treatment plans for all our patients, including high fluid intake and a low-salt diet. Medications may be prescribed to help dissolve the stones or prevent new ones. These include thiazide diuretics to lower the levels of calcium in the urine and potassium citrate to treat low urine citrate and help alkalinize the urine to help prevent calcium oxalate stone formation. Citrate is generally good to have in the urine. In fact, we encourage children to drink lemonade because it may be a source of natural citrate. Magnesium therapy is also used to help prevent stones. After a child has his first stone and we've completed our initial evaluation, we like to see him twice a year. We check to see how he's drinking, monitor his
symptoms and do follow-up urine and blood tests. We assess for development of new stones by follow-up ultrasound.
