Urolithiasis in children
As the prevalence of stone disease has grown, so has the importance of understanding disease process, diagnosis, and management.
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.
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.
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
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
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.
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.