Nephrolithiasis in Children: Medical Management
Gregory E. Tasian
Nephrolithiasis (kidney stone disease) is a disorder of mineral metabolism characterized by acute painful presentations that recur for many patients. Nephrolithiasis has been associated with extrarenal diseases including cardiovascular disease, hypertension, diabetes, low bone-mineral density, and chronic kidney disease. Contrary to historic literature, most kidney stones that occur during childhood are not due to rare, inherited monogenic disorders such as cystinuria. As in adults, calcium-based stones are the most common type of kidney stones that develop during childhood. Currently, the prevalence of kidney stones is approximately 9%, which represents a 70% increase since the 1990s. Recent studies have shown the incidence of stone disease has increased substantially among children, with the greatest increases observed among adolescent females. The cause of the shift in the epidemiology of kidney disease over a short time period is unclear. The risk of nephrolithiasis is determined by the interaction of genetics, behaviors, and environmental exposures. This chapter will review the presentation, causes, evaluation, and medical treatment of urolithiasis in children.
A. The following factors are known to affect the formation of kidney stones.
3. Hyperuricosuria (uncommon in children)
5. Low urine volume
6. Acid urine pH (uric acid stones, which are rare in children)
7. Alkaline urine pH (calcium phosphate stones).
Hypercalciuria is most commonly idiopathic. It is exacerbated by high dietary intake of salt and protein. Hypocitraturia may be idiopathic or related to metabolic acidosis, as in chronic kidney disease, chronic diarrheal states, and high protein diet. Hyperuricosuria is typically due to dietary purine excess and very rarely to genetic mutation.
B. Comorbid Disease
Other medical conditions increase the risk of nephrolithiasis by affecting urine chemistries, volume, and/or pH.
1. Metabolic disorders
a. Hypercalciuric states
(1) Idiopathic hypercalciuria
(2) Primary hyperparathyroidism
(3) Renal tubular acidosis
(4) Corticosteroid excess
(6) Medullary sponge kidney
(7) Phosphorus depletion
(8) Vitamin D intoxication
(9) Idiopathic hypercalcemia of infancy
(11) Bartter syndrome
(12) Furosemide use in infants
(1) Primary hyperoxaluria (types I, II, and III)
(2) Enteric hyperoxaluria from inflammatory bowel disease (e.g., Crohn’s disease) and malabsorption (intestinal bypass)
(1) Leukemia, lymphoma
(2) Idiopathic, familial
(3) Inborn error of metabolism: hypoxanthine-guanine phosphoribosyltransferase deficiency (Lesch-Nyhan syndrome)
(4) Glycogen storage disease, type I
(1) Renal tubular acidosis
(2) Medullary sponge kidney
(3) Malabsorption syndromes
g. Orotic aciduria
2. Abnormalities of the urinary tract
a. Ureteropelvic junction obstruction
b. Vesicoureteral reflux
c. Neurogenic bladder
e. Ileal conduit, ureterosigmoidostomy
f. Bladder exstrophy.
III. INITIAL MANIFESTATIONS
Similar to adults, children with nephrolithiasis often present with the following symptoms.
D. Incidental stone on diagnostic imaging.
The frequency of these findings varies with age. Classic flank pain may not be seen in children, particularly those under 5 years of age.
IV. STONE COMPOSITION
Contemporary analyses of the mineral composition of kidney stones in children demonstrate that approximately 85% are calcium-based. The approximate proportion of stone types classified by the main component are as follows.
A. Calcium oxalate 75% to 80%
B. Calcium phosphate 10% to 15%
C. Magnesium ammonium phosphate (struvite) 5% to 10%
D. Cystine 1%
E. Other 1%.
The historic incidence of struvite stones is approximately two-fold higher in young children 0 to 5 years of age, than in adolescent patients. This reflects a higher association of urinary tract infection with stones in infants than in older children.
V. EVALUATION OF THE CHILD WITH UROLITHIASIS
A. Ultrasound should be used as the initial imaging study for children with suspected nephrolithiasis reserving CT only for children with a nondiagnostic ultrasound in whom the clinical suspicion for stones remains high. Although ultrasound is less sensitive and less specific than CT, ultrasound accurately identifies most clinically significant kidney stones in children. The diagnostic criteria for identifying a kidney stone are: (1) echogenic focus on greyscale image; (2) posterior acoustic shadow (often not seen on modern ultrasound machines); and (3) “twinkle” artifact on Doppler.