STEAMBOAT SPRINGS, COLO. – Kidney stones, historically considered an adult malady, have become vastly more common among children during the past decade, in concert with the obesity epidemic.
Moreover, the clinical presentation of urolithiasis in children is often different than it is in adults. As a result, physicians are frequently caught off guard.
Dr. Beth A. Vogt
"The diagnosis of kidney stones is often not the first thing on the differential diagnosis list – or even on the list – for a child with abdominal pain," Dr. Beth A. Vogt observed at a meeting on practical pediatrics sponsored by the American Academy of Pediatrics.
The younger the child with a kidney stone, the more likely the clinical presentation will be nonspecific abdominal pain rather than the flank pain or renal colic typical in affected adults, according to Dr. Vogt, a pediatric nephrologist at Case Western Reserve University, Cleveland.
Thus, in the child with nonspecific abdominal pain, it’s important to add urolithiasis to the differential diagnosis list, which classically has included viral gastroenteritis, appendicitis, cholecystitis, intussusception, and food poisoning, she said.
Gross hematuria is present in 30%-40% of children who present with kidney stones. Dysuria is also common. In addition, asymptomatic kidney stones are frequently detected incidentally in children undergoing ultrasound or CT following traumatic injury.
The primary care physician’s role in pediatric urolithiasis is to make the diagnosis, begin acute management with hydration and pain control, hospitalize if necessary, and refer the patient to urology for intervention if the stone is so large it’s unlikely to pass.
Also, referral to a nephrologist is recommended after a first-ever stone has passed and the child has resumed normal activities. The nephrologist’s job is to figure out why the child is forming stones and to come up with a specific prevention plan (for example, a low-sodium diet in patients with hypercalciuria, or antibiotics in children with infection-related struvite stones), Dr. Vogt continued.
"In adults, the standard practice is to wait until they prove to be recurrent stone formers before doing a work-up. That’s not the case in children. Don’t wait until after a child has had several stones to refer to nephrology. We find something metabolically wrong in about 75% of the kids," she said.
The diagnosis of pediatric urolithiasis is suggested by the combination of abdominal or flank pain, hematuria on a urine dipstick test, and crystals in the urine upon microscopic examination. A couple of caveats, though: Recent studies indicate that up to 15% of kids with active stone disease have a negative urinalysis, so urolithiasis can’t be ruled out on the basis of a negative urine dipstick. Also, many children who don’t have kidney stone disease have crystals in their urine.
The best initial diagnostic imaging study is kidney ultrasound. It doesn’t involve radiation, which is an important advantage because some young patients will continue making stones and will therefore need to undergo imaging many times.
Ultrasound is very good at identifying stones in the renal parenchyma, but not ureteral stones or very small stones. So if the clinical picture and laboratory results suggest urolithiasis but the ultrasound is negative, it’s time to move on to CT without contrast, by far the most sensitive test. It is ordered by requesting a "CT stone protocol."
Acute management of stone disease entails oral or intravenous hydration to push the stone through the urinary tract. Pain medication is important. Tamsulosin (Flomax) is prescribed off label to induce ureteral relaxation and assist in the stone’s passage. It’s useful to have the patient use a urine-straining device to try to catch the stone for later analysis.
"The diagnosis of kidney stones is often not the first thing on the differential diagnosis list – or even on the list – for a child with abdominal pain."
Urologists consistently recommend a 4- to 6-week trial of spontaneous passage, provided the child doesn’t have a urinary tract infection, is able to hydrate orally, and obtains pain control with oral medications.
"When you tell that to parents, they say, ‘Are you kidding?’ That’s a long, long time. Parents don’t like it," Dr. Vogt said.
A stone larger than 10 mm is so unlikely to pass spontaneously that Dr. Vogt recommends going straight to urologic intervention. A stone less than 5 mm will usually pass spontaneously, even in a child.
Urologists will typically place a ureter-long stent in a patient with refractory nausea and vomiting or an infection. This allows urine to bypass an obstructive stone.
"It buys you time. It gets the patient out of the cycle of pain, vomiting, and renal colic," she explained.