Kidney stones (Nephrolithiasis) in children
Alex Constantinescu, MD
It has become more frequent than a weekly office encounter with children who complain of symptoms of, or have risk factors for, kidney stones (also known as calculi). The exact incidence of kidney stones in children is unknown, although multiple studies have pointed out an increase over the recent years, and the lower age at presentation, making nephrolithiasis a disease of all ages.
How do patients develop kidney stones? Without complicating the subject, a brief explanation follows: the balance between “stone-forming” elements (calcium, oxalate, uric acid, etc.) and “stone-inhibiting” elements (citrate, potassium, magnesium, among others), in the urine of these patients, is tilted in favor of precipitation of crystals. By apposition, plaques are being formed in the areas of the kidneys called papillae. Over time, the plaques fall into the collecting system, and if conditions are favorable, the calculi become larger. Sometimes, if small enough, they can be eliminated. In other instances, larger calculi can cause blockage of urine passageways, or other symptoms described below.
Common symptoms of kidney stones which usually prompt a consultation with the nephrologist or the urologist are:
- blood in urine
- pain on urination
- urinary incontinence
- ill-defined abdominal pain or back pain (with or without nausea and/or vomiting, constellation known as “renal colic”)
- urinary tract infection
What leads to nephrolithiasis? Family history of kidney stones or certain types of kidney disease (such as polycystic kidney disease, medullary sponge kidney) would suggest the need to evaluate the child for risks of nephrolithiasis. Though genetic causes can be identified in some cases, a few metabolic abnormalities, such as cystinuria and renal tubular acidosis (associated with hypercalciuria and hypocitraturia) can be incriminated in others. Nevertheless, some predisposing factors are well known:
- certain types of diuretics (furosemide)
- medications that alter the ability of the kidneys to acidify the urine (acetazolamide)
- prolonged steroid therapy
- excess calcium and vitamin D
Inadequate diet plays a major role in kidney stone formation. For instance, insufficient fluid intake and excess sodium are common risk factors, independent of stone composition, especially in the region called “the stone belt” (comprised mostly of the Southern US). Certain foods high in oxalate (chocolate, tea, peanut butter, etc.), or foods with normal content of oxalate eaten along with inadequate calcium-containing foods, can lead to calcium oxalate stones, independent of family risk factors. Also, excessive protein intake could lead to uric acid stones.
How are kidney stones diagnosed and treated? Ideally, one would like to retrieve the calculus and send it for analysis to determine its exact composition. Quite often they are mixed stones, making the management extremely difficult. In order to detect the stone burden (amount of kidney stones in the kidney tissue), an ultrasound screening could detect stones larger than 3 mm in diameter, as well as consequences of obstructing (blocking) stones. When stones are small, a non-contrast CT scan is needed. However, this would not be a useful study for follow-up, due to the amount of radiation and cost. Depending on the age, small stones (less than 5 mm in diameter), can be eliminated spontaneously. Stones measuring between 5 and 10 mm may be eliminated by older children, though younger children may require urological intervention. Stones measuring approximately 1 cm in diameter, more often require urological (surgical) intervention.
More and more centers have started focusing on the prevention of kidney stone disease, where nephrologists and urologists work together with nutritionists and radiologists to identify early on the risk factors in these patients, assess their stone burden, and emphasizing the need to minimize surgical intervention. The ultimate goal is to preserve the renal function, as well as prevent complications from nephrolithiasis, which could culminate with renal failure. Obviously, more research is needed to identify genetic predisposition and tailor diet and drug therapy based on the patients’ characteristics.