Stone Disease

pebble towerStone disease in children, or renal colic, is much more common than pediatricians think.

INCIDENCE

The exact incidence is unknown. There is probably no sex difference.

CLINICAL PRESENTATION

The most important factor in the diagnosis of stone disease in children is to consider it in the differential diagnosis.

Many of these children will complain of abdominal pain, and many will be misdiagnosed and evaluated for appendicitis. Many stones in children, especially small calculi, will pass spontaneously. Some patients may not have much in the way of pain but present with hematuria or symptoms of a urinary tract infection with a fever. Rarely, bilateral upper urinary tract calculi may obstruct the urinary tract; and the patient will present with anuria or azotemia. Bladder calculi can be quite irritating, and these patients often have marked dysuria and/or strangury, hematuria and a urinary tract infection. In this country, children with bladder calculi have usually had some sort of urogenital surgery or Foley catheterization.

PHYSICAL EXAM

It is not uncommon for the patient to present with signs suggestive of appendicitis, especially when the stone is on the right side. However, an inflamed appendix lying on the ureter or on the bladder may also demonstrate pyuria. In those boy with voiding difficulty, a stone may be palpated in the urethra. If the boy has had hypospadias surgery, a urethral stricture may predispose to stone formation.

Urinalysis will often demonstrate hematuria and pyuria, and the urine should be cultured.

INVESTIGATIONS

The intravenous pyelogram (IVP) will confirm the diagnosis of calculi in most instances; oblique views may be essential. Delayed views are also important, in case the stone cannot be seen when overlying the bony pelvis. Calcium and cystine stones are all radio-opaque and can be detected on plain film of the abdomen. On the other hand, uric acid stones and xanthine stones are all radiolucent and will be detected only after contrast medium has been injected, and then only by virtue of obstruction or radiolucent filling defects.

Investigations for metabolic sources of stone formation must be individualized. After screening for hypercalcemia, hyperuricemia, cystinuria and infection, stone analysis of the recovered stone will help direct further evaluation of the patient.

STONE TYPE

Stones may be primary, arising as a result of a metabolic problem or idiopathic, or secondary to such factors such as infections, stasis or a foreign body.

Factors that directly affect stone formation are urinary pH, solute load, stasis and urinary tract infection. Inhibitors of stone formation include magnesium citrate, pyrophosphates and other polyphosphates.

Most calculi seen in children are idiopathic, i.e., without obvious cause.

IDIOPATHIC RENAL LITHIASIS

The syndrome of idiopathic renal lithiasis is by far the most common cause of stone formation and is only diagnosed by exclusion.

1. Normocalciuria accounts for about 75% of idiopathic stone formers.

2. Absorptive hypercalciuria. This results from intestinal hyper-absorption of calcium.

3. Renal hypercalciuria. This results from the impairment of renal tubular reabsorption of calcium (renal leak).

PRIMARY DISORDERS

1. Renal tubular acidosis (Type I).

This is a metabolic defect in which the distal renal tubule is unable to maintain a pH gradient between the blood and the tubular urine. As a result, there is hyperchloremic acidosis and an increased urinary loss of sodium, potassium, calcium and phosphorus.

Because the kidney in patients with renal tubular acidosis is unable to acidify urine below a pH of 6, the disorder can easily be identified.

Patients with renal tubular acidosis are treated with Polycitra.

Type II renal tubular acidosis is a proximal tubular disorder of bicarbonate reabsorption and is not associated with renal calculi.

2. Cystinuria.

This is inherited as an autosomal recessive trait. Homozygotes excrete cystine over 500 mg per day. It is only the homozygote which forms stones; the heterozygote does not.

Cystinuria is best treated with fluids and alkalinization with medications such as Polycitra.

3. Hypercalcemic states.

A. Primary hyperparathyroidism. Unusual in childhood.

B. Sarcoidosis.

C. Hypervitaminosis D.

D. Milk-alkali syndrome.

E. Neoplasms.

F. Cushing’s syndrome.

G. Hyperthyroidism.

H. Idiopathic infantile hypercalcemia is an inborn error of metabolism of Vitamin D. These patients also usually have nephrocalcinosis. The blue-diaper syndrome results from a defect in the intestinal transport of tryptophan.

I. Immobilization.

4. Uric acid stones.

These are rare in children but may be seen in patients being treated for leukemia. An inborn error of metabolism that may result in uric acid stone formation is the Lesch-Nyhan Syndrome.

5. Nephrolithiasis

Nephrolithiasis and intestinal disease may be seen in those with Crohn’s, chronic pancreatitis, non-tropical sprue, etc.

6. Infected urolithiasis and urinary stasis

Infected urolithiasis and urinary stasis may be seen as a complication of obstruction and/or urosepsis. The UTI is often caused by urea-splitting bacteria such as Proteus.

7. Others include glycinuria, hyperoxaluria and xanthinuria.

These are rare genetic disorders resulting in particular types of stone formation.

TREATMENT

Treatment of stone disease in children has two parts, the acute problem and the chronic management.

The acute problem entails management of pain relief, hydration, treatment of infection, relief of any obstruction, and recovery of the calculus for analysis. Many small calculi will pass spontaneously with conservative management. Some may be encouraged to pass after placing the patient on theophylline to relax the ureteral smooth muscle. Antibiotics will be required if the patient has any systemic signs of sepsis. Certainly, urgent intervention to relieve the obstruction will be required in the face of sepsis.

Ureteral obstruction and hydronephrosis without infection can be managed expectantly for short periods without renal damage as long as the patient can cope.

Indications for early surgical intervention include high-grade obstruction, severe uncontrollable pain, an unresponsive urinary tract infection, or a solitary kidney.

If the stone is in the pelvic ureter, the stone can be treated in most children using laser lithotripsy through ureteroscopic means under general anesthesia and fluoroscopic control. (See the laser section.)

Stones above the pelvic brim may require a stent and then ESWL. However, in elective ESWL, stenting is usually unnecessary. Surgical removal of the stone can usually be handled through one of these two modalities, and open procedures are rarely required.

The chronic management of stone disease depends upon the stone analysis, whether or not this was simply an isolated event, and also whether there are additional stones present in the kidneys.