Urolithiasis in children

Irene M McAleer, MD, JD, MBAUrolithiasis occurrence is increasing in both adults and children in the United States, with nearly 1 in 11 adults having a stone at some time in their life.¹ Unfortunately, stone occurrence in children also appears to have increased from 1% to 2% in the 1950s to 1970s to almost 10%, where previously the rate of stone incidence was only 18 per 100,000 in 1999 to 57 per 100,000 in 2008. Adolescent girls (aged 12 to 18 years) have a higher rate of occurrence than the other groups studied, although the overall sex distribution in all age ranges was about the same.

Hospital admission rates for urolithiasis increased to 1 in 685 admissions in the 2002 to 2007 time period.

With more children and adolescents developing kidney and ureteral stones, it is critical that the pediatric care community (pediatricians, nurse practitioners, primary care providers, and family medicine physicians) understands how to evaluate, treat, and prevent recurrence of stones in their patients. This article provides background on the risk factors for stone disease, its presentation in children, and the changes in diet that increase that risk, and offers practical tips on the evaluation, treatment, and prevention of stones.

Risk factors

Pediatric stone disease has different geographic and racial prevalence rates. Stones are very common in the Middle East, Pakistan, India, and Southeast Asia. Children in developing countries tend to have more bladder calculi than calculi elsewhere in the urinary tract. Bladder stone composition in these children consists predominantly of ammonium acid, uric acid, and urate, likely because of the relatively low availability of dietary phosphate in these countries.²

Children of African descent worldwide rarely have stones, whereas in the United States, Caucasian children are more likely to suffer from urolithiasis, especially if they are from the Southeast region. Stones are more likely to be found in the kidneys and ureters than in the bladder in American children.

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Previously, most children who developed kidney stones also had anatomic abnormalities that increased their likelihood to develop stones, such as obstruction of the ureter or renal pelvis, exstrophy, or static drainage with horseshoe kidney or megaureter. Now, between 40% and 50% of children with urolithiasis have metabolic abnormalities identified, whereas only 30% of stones are associated with genitourinary abnormalities. Most likely, the children with anatomic abnormalities and urolithiasis have concomitant metabolic risk factors.

Diet

Much of the increased incidence in stone formation in children and adolescents is attributed to major dietary changes in the United States over the past few years. The Centers for Disease Control and Prevention (CDC) recently published that the prevalence of obesity in children aged 2 to 19 years is about 17%, affecting about 12.7 million children and adolescents. The prevalence is particularly high in Hispanics (21.9%) and non-Hispanic blacks (19.5%), while it is only 14.7% in non-Hispanic white children.³

Children, particularly adolescents, are not drinking as much water or milk as they did previously. Increased consumption of sugary drinks has added to the increased obesity rates in children. Increased sodium consumption through processed foods also has increased stone formation through increased urine calcium excretion.

The most common abnormalities found have been hypercalcuria and hypocitraturia. Other metabolic problems seen, but less frequently, in children are hyperoxaluria, cystinuria, and hyperuricosuria. The most common stones found in US children are calcium oxalate (40% to 65% of all stones), calcium phosphate (14% to 30%), magnesium ammonium phosphate (struvite, 10% to 20%), cystine (5% to 10%), and uric acid (only 1% to 4%). In children, increased uric acid in urine promotes calcium oxalate stone formation, whereas uric acid stones are more commonly seen in adults.

NEXT: Obesity and hormones as risk factors

Stones form when there is a supersaturation of these minerals. Promotion of crystallization through low total urine volume, increased concentrations of stone-forming ions, and decreased concentrations of inhibitors of crystallization all have been implicated in the increased rate of stones in children. As mentioned previously, children notoriously fail to have adequate fluid intake, particularly water intake. They also are more likely to drink beverages that increase their risk of stone formation, such as dark, caffeinated, sugary sodas. These trends have been increasing over the past 10 years, as have “fad diets” that may increase risk of stone formation when used in combination with low-volume or high-sugar-content fluid intake.

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Low-carbohydrate or high-protein diets or vegan diets that may be high in oxalate intake are becoming more prevalent in children and adolescents. Vegan diets also increase the risk of hyperuricemia and hyperoxaluria from increased intake of foods high in oxalates (such as kale, spinach, and rhubarb). Many of these diets restrict intake of milk or dairy products necessary to keep adequate calcium intake that allows binding of calcium to ingested oxalates, as well as being high in salt intake. The fruits and vegetables eaten in such diets are the main sources of dietary oxalates. These diets contribute to a high dietary load of oxalates and, if calcium is restricted, will actually increase risk of calcium oxalate stone formation.⁴

In the past, by contrast, high milk intake helped children maintain adequate calcium intake to prevent stones. Appropriate calcium intake decreases the absorption of oxalate in the intestines, preventing increased oxalate excretion by the kidneys that potentiates stone formation.

Sodium intake

Increased sodium intake by children in the United States is also rising above recommended dietary allowances. This increase in body sodium increases the excretion of urinary calcium, which promotes supersaturation of calcium and subsequent stone formation.^2,5

Obesity

Increased obesity in children also may be putting them at risk for stone formation, as is being seen in adults. Obesity causes a decrease in urine pH and increased excretion of sodium, phosphorous, and oxalate, increasing the rate of stone formation. As the rate of childhood obesity tripled from 1980 to 2002, obesity as a cause of increased stone rate in children has not been as well founded as it has been in adults.³

Hormones

Increases in stone occurrence in adolescent girls may be hormonally driven by estrogen increases with the onset of puberty. Similarly, it has been found that hormone replacement therapy, particularly using estrogen supplements, in postmenopausal women causes a decrease in calcium excretion and an increase in citrate secretion. However, postmenopausal women have an increased stone rate over premenopausal women possibly from increased calcium oxalate supersaturation seen in the estrogen supplemented group. Thus, increased estrogen levels in adolescent girls and postmenopausal women on supplements may cause higher stone prevalence attributed to increased calcium oxalate supersaturation.

Seizure medications

Additionally, children with seizure disorders who are placed on a ketogenic diet or high-protein diet to prevent seizures have a higher risk of stone formation. The high-protein intake in these diets may raise urinary oxalate excretion increasing the likelihood of urinary lithogenesis. In this population, antiseizure medications (topiramate and zonisamide) are known to potentiate stone formation by increasing hypocitraturia. Also, these children frequently are fluid restricted or cannot adequately hydrate themselves to offset citrate loss.

Stone presentation in older children is similar to adult stone presentation, commonly flank pain, abdominal pain, nausea, and vomiting. Younger children do not always present this way. In fact, only 10% to 14% of younger children present with typical acute renal colic symptoms. These children tend to have vague symptoms and less localized pain but may present with hematuria or urinary tract infection.

NEXT: Diagnosis, treatment, and prevention

Diagnosis, treatment, and prevention

Although many children and adolescents with urolithiasis present with abdominal or colicky flank pain, similar to adults, many children may have nonspecific symptoms, such as generalized abdominal pain, nausea, vomiting, or nonspecific findings consistent with urinary tract infection. Many children will have gross hematuria as initial presenting sign of urolithiasis.

Treatment of children with renal stones is actually similar to that of adults. Many children will pass similarly sized stones as adults. Fifty percent of children will pass stones 4 mm to 5 mm in size regardless of the child’s size. Increased hydration and pain management with either nonsteroidal anti-inflammatory drugs (NSAIDs) or, rarely, narcotics help children manage their symptoms while passing a stone. Many children can be treated as outpatients and do not require hospital admission on presentation or when symptoms are controllable.

Alpha-adrenergic blockade (tamsulosin) has been used in children as well. The use of stone expulsion treatment particularly to facilitate passage of distal ureteral stones appears to have similar success in children as in adults and the medications are well tolerated by children, although current studies are limited.

Long-term prevention includes increased fluid intake, particularly water, up to 2 liters per day to 2.5 L/d in adolescents, or more in cystine stone formers. Improved fluid intake and salt and sugary drink limitations are critical for prevention of recurrence of stones in most children and adolescents, but are difficult to achieve, just as these improvements are similarly difficult to achieve in adults.

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Specific treatments depend, if possible, on obtaining urine and serum testing for causative factors in stone formation. This is somewhat difficult in the non–toilet-trained child, where obtaining a 24-hour urine collection would require an indwelling catheter and bag collection. Spot urine tests for causative factors have been performed and can be helpful in determining specific metabolic abnormalities that the child may have and may help direct preventive treatment.

Decreasing high animal protein intake and sodium intake are important in any dietary recommendations for stone prevention, as is appropriate intake of potassium, calcium, and magnesium, which are protective against oxalate composite stone formation.

Potassium citrate (2-4 mEq/kg/d) is also a mainstay in preventive treatment in children at risk for stone formation because of underlying metabolic abnormalities, but it is not very palatable and may be hard to give to children for the 2 to 3 times a day that may be needed to improve urinary citrate concentrations.^2,5 Potassium citrate is found in several clear lemon-lime soft drinks (such as Sprite, 7UP or Mist Twst [formerly Sierra Mist]) that are generally more palatable to children, may be less costly than prescription potassium citrate, are available in sugar-free forms, and have the additional advantage of increasing fluid intake while improving urinary citrate levels.

Radiologic evaluation for urolithiasis in children is predicated on ALARA (as low as reasonably achievable) techniques. Adult patients are generally evaluated with high-radiation testing such as computer tomography for diagnosis, treatment, and surveillance. These high-radiation techniques are rarely needed in children unless there is some uncertainty as to diagnosis or conflicting findings on low-radiation techniques that are generally used.

It is easy to obtain an abdominal flat plate (KUB [kidneys, ureter, bladder]) and ultrasound imaging of the kidneys and bladder, as these tests will find most stones because the majority of stones in children are radiopaque. Furthermore, most large stones in the kidney or ureter near the bladder that may need interventional treatment will be found on these studies.⁵ Smaller stones, as mentioned, tend to pass spontaneously and may be inferred if not directly seen by the presence of hydronephrosis or hydroureteronephrosis in ultrasonography (Figures 1 and 2).

NEXT: Surgical techniques

Surgical techniques

Although many stones will pass spontaneously, some children may require surgical treatment for their stones. Surgical techniques used in removing stones in adults are similarly successful in children. Children should be referred to a pediatric urologist or general urologist if they have stones that are generally larger than 7 mm to 8 mm, as these are less like to pass spontaneously; if their stones do not appear to pass in a reasonable time frame (generally should pass or move from the initial stone location on evaluation in about 4-6 weeks); or if the patient has a congenital or acquired anatomic abnormality increasing the risk of stone formation or decreasing the likelihood of passing the stones spontaneously.

Treatment options include ureteroscopy with or without lithotripsy, percutaneous nephrolithotomy with or without lithotripsy, and extracorporeal shock wave lithotripsy (ESWL).⁵ Open and minimally invasive procedures also can be considered but are currently less often used in both children and adults.

Interestingly, although ESWL is less successful when used in adults because of poor stone-free rates, ESWL treatment for renal stones in children, including fairly large stones, tends to be more successful when used in children and achieves reasonable stone-free rates (Figures 3 and 4).

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) has a helpful information publication in English that explains kidney stone formation, management, and treatment that is available online for families and pediatrician offices at www.kidney.niddk.nih.gov(“Kidney Stones in Children,” NIH Publication No. 11-7383, September 2011).

Summary

Urolithiasis is becoming much more prevalent in children of all ages, and it needs to be treated aggressively with prevention. Many of these children will be seen by their primary care physician or nurse practitioner who needs to consider urolithiasis as a diagnosis in children presenting with gross hematuria as well as various degrees of abdominal or colicky pain.

Prevention of stone recurrence depends upon ongoing increased hydration, limited salt intake, and improved dietary intake. Spot urine or 24-hour urine collection for stone risk will help determine certain dietary changes specific for metabolic abnormalities found on evaluation.

Radiographic testing can diagnose stones in most children, however, limiting use of ionizing radiation is imperative to reduce lifetime risk of radiation exposure in children who are likely to have recurrence rates similar to adults.

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Most children will not need surgical intervention for their stone disease, but referral to pediatric urology may be necessary for large stones, complicated patient anatomy, and for stones that do not pass in a reasonable time period. The techniques used in adults work equally well in children.

REFERENCES

1.    Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014;192(2):316-324.

2.    Copelovitch L. Urolithiasis in children. Pediatr Clin North Am. 2012;59(4):881-896.

3.    Ogden CL, Carroll MD, Fryar CD, Flegal KM. Prevalence of obesity among adults and youth: United States, 2011–2014. NCHS data brief, no 219. Hyattsville, MD: National Center for Health Statistics; 2015.

4.    Novenne A, Ticinese A, Morelli I, Guida L, Borghi L, Meschi T. Fad diets and their effect on urinary stone formation. Transl Androl Urol. 2014;3(3):303-312.

5.    Hernandez JD, Ellison JS, Lendvay TS. Current trends, evaluation, and management of pediatric nephrolithiasis. JAMA Pediatr. 2015;169(10):964-970.