Treating pediatric kidney stones: Overcoming obstacles and ambiguity
Although kidney stones are rare in children – affecting between 36 and 145 children per 100,000 – incidence has increased steadily in recent years. This is especially true in states comprising the “kidney stone belt” in the southern U.S.
These stones can have a variety of potential causes, ranging from an underlying genetic condition to response to medication or a child’s dietary habits. Identifying the cause and selecting the appropriate treatment is a complex endeavor, often requiring expertise in both nephrology and urology.
About 300 patients from Texas and nearby come to Children’s Health℠ for kidney stone evaluation each year. There, the Pediatric Comprehensive Stone Center has developed a multidisciplinary approach to treating and preventing stones that can be a model for other physicians to follow.
“Recurrent kidney stones can lead to irreparable damage and, rarely, even kidney failure, so it’s critical to understand exactly why a child forms stones and stop that process from continuing,” says Matthias Wolf, M.D., Pediatric Nephrologist at Children’s Health and Associate Professor at UT Southwestern. “Without appropriate care, this is a problem they are likely to face again and again.”
Identifying the type of pediatric kidney stone
The key to treating a patient’s kidney stone is identifying what it’s made of. A stone made of cystine, for example, suggests the patient has the genetic disease cystinuria. Other diseases cause stones composed of calcium, oxalate, phosphate or other materials.
Knowing the exact composition is important because different stones form as a result of different processes. To help the child avoid future stones, you have to be sure you’re treating the right process.
“A calcium oxalate stone is usually treated by increasing the urinary pH through citrate therapy or an alkalinizing agent — but other kinds of stones may get worse if you take that approach,” says Dr. Wolf.
The best way to identify a stone’s contents is by chemically analyzing the stone. Getting a stone sample, however, isn’t always easy. To avoid a procedure requiring anesthesia, the Children’s Health team usually asks patients to collect a sample when they pass the stone during urination. A coffee filter will do the trick. But passing stones through the ureter is a notoriously painful process, and many patients fail to think about filtering their urine during or after that experience.
“If we can’t get a stone sample, we do blood and 24-hour urine tests to create a kidney stone risk profile and determine the likely cause,” adds Dr. Wolf.
Multi-dimensional analysis of possible causes
While a stone’s chemical components provide vital clues, often they fill in only part of the picture. A calcium oxalate stone, for example, can have many different ultimate causes, such as primary hyperoxaluria or Bartter syndrome, along with exacerbating factors like a high-sodium diet or dehydration.
So the team gathers information of multiple kinds to help make a diagnosis. This includes dietary habits and family history of stone formation. Sixty percent of children that form stones have kin that make kidney stones, suggesting that there are inherited genes that contribute to the risk of making kidney stones.
Still, some kidney stones defy explanation.
“In that case, we present patients at a quarterly meeting with our colleagues at UT Southwestern,” says Jyothsna Gattineni, M.D., Pediatric Nephrologist at Children’s Health and Associate Professor at UT Southwestern, who co-leads the kidney stone clinic with Pediatric Urologist and UT Southwestern Professor Linda Baker, M.D.
Recent cases reviewed by the team include a baby who has a rare mutation in the PNPT1 gene and other comorbidities. The patient passed a uric acid stone and has progressive kidney disease, neither of which have been documented previously in patients with that genetic mutation.
The team considered the stone might be caused by increased serum uric acid levels and acidic urine. Dr. Gattineni prescribed medications to decrease serum uric acid levels and alkalinize the urine, and the patient is now stone-free.
“But the cause for progressive kidney disease remains elusive, so now we are researching possible metabolic pathways,” says Dr. Gattineni.
Choosing the right treatment pathway
Treatments at the clinic are multidisciplinary: Urology leads the way on acute surgical care of stones that cause severe pain and obstruct the flow of urine, while nephrology focuses on prevention and long-term care. The form of acute care depends on the size and location of a stone. Some stones may be small but not obstructive or painful, and the team may choose only to monitor.
When stones risk or cause problems like closing off the ureter, the team intervenes. Kidney obstruction, where the urine cannot leave the kidney because the stone is blocking the ureter, is what causes the typical rapid onset pain and vomiting. A kidney cannot be left blocked for more than a few weeks without permanent kidney damage occurring. So this situation may require hospital admission for symptom relief and possibly surgery.
Small to moderate stones may require ureteroscopy. Very large stones typically require percutaneous nephrolithotomy (PCNL). And if an obstructing stone is accompanied by a urine infection or fever, then it becomes an emergency operation to drain the infected urine by inserting a ureteral stent to prevent the infection progressing into the bloodstream with sepsis.
When a stone is likely to cause problems but hasn’t done so yet, the team may recommend extracorporeal shock wave lithotripsy (ESWL). This is a non-invasive, elective procedure suited to moderate to large-sized stones, or for patients with complex conditions or physiology that rule out other treatments.
“We are one of the only pediatric hospitals that owns our own ESWL machine, and our anesthesia team is experienced with kids of all sizes,” says Dr. Baker.
To prevent future stones, the team often prescribes medication or supplements and coordinates with other specialists. Nutritionists develop and adjust dietary plans, such as decreasing salt intake and increasing citrate to alkalinize the urine.
“That means orange juice, not lime or lemon, because the goal is to alkalinize the urine by providing potassium citrate present in orange juice compared to citric acid in lime/lemon juice,” says Dr. Gattineni.
Thus, it is important for patients to increase fluid intake and reduce salt intake, but not to restrict calcium in the diet, even though many stones contain calcium. This is because children who form kidney stones often have associated bone disease, and reducing calcium will only make their bones weaker. Physical therapy is often prescribed for these patients, to help encourage bone generation and density.
“Even for patients who are immobile, physical therapy can help prevent their bones from leaking calcium and forming stones,” Dr. Wolf says.
Expanding knowledge of pediatric kidney stones
The clinic participates in clinical research to improve the treatment of pediatric kidney stones. This includes the PUSH trial with the NIH, which is testing different methods of increasing patient hydration, and a Pediatric KIDney Stone (PKIDS) Care Network study comparing the effectiveness of the three stone-removal procedures for different kinds of patients.
“Most of the scientific data on kidney stones is based on adults, so these studies should help reduce the mystery on how to help kids specifically,” Dr. Baker says.
Image disclaimer: This photo was taken in 2018 prior to COVID-19. See our system COVID-19 safety measures.
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