Case 2: An unusual cause of urinary symptoms

A 3.5-year-old Mexican-American boy presented to the emergency department with a three-month history of increasing dysuria, voluntary urinary retention and ‘dribbling’. The pain was described as severe, and was localized to the penis and periumbilical area. His mother reported that he had cried on urination since infancy, and although doctors in Mexico had recommended a circumcision, the procedure was never performed. He was otherwise asymptomatic, without fevers or gastrointestinal symptoms. He avoided liquids in an effort to minimize urination, consuming less than 1 L a day. After refusing to urinate for as long as possible, he would exhibit overflow incontinence for several hours. There was no history of prescription or over-the-counter medication use.

Past medical history was otherwise unremarkable. Neither his three older siblings nor his parents exhibited similar symptoms at the time. The child's paternal grandmother had a history of nephrolithiasis resulting in renal failure and nephrectomy. His father had a history of dysuria as a child, for which he was circumcised without further incident. Review of systems was unremarkable.

Physical examination revealed an anxious but well-appearing boy. His vital signs were normal, and his height and weight were at the 40th percentile. Abdominal palpation did not elicit pain, and no masses were detected. There was no “flank” tenderness. His rectal tone was normal, as was the neurological examination of the legs. The penis was uncircumcised without any gross abnormalities of the foreskin or urethral meatus. The penis was not tender to palpation, and the foreskin was easily retractable.

Initial laboratory studies included a normal complete blood count, albumin, phosphate, blood urea nitrogen and creatinine. The chemistry panel revealed a normal anion gap acidosis with a sodium of 135 mmol/L, potassium of 3.3 mmol/L, chloride of 106 mmol/L and bicarbonate of 17 mmol/L. This acidosis resolved itself over the course of hospitalization with intravenous hydration. Urine was collected by catheterization, and urinalysis revealed 3+ leukocyte esterase, positive nitrites, pH of 6.5, 1+ protein, 3+ blood, 25 to 50 white blood cells/high power field, eight to 25 red blood cells/high power field, no casts and many bacteria. Urine culture grew greater than 100,000 colony forming units/mL of Escherichia coli, Morganella morganii and Enterococcus faecalis. Further investigation elucidated the underlying problem.

CASE 2 DIAGNOSIS: BLADDER CALCULUS WITH CHRONIC URINARY TRACT INFECTION

Abdominal x-ray and ultrasound revealed a freely mobile, radiopaque calculus in the bladder, measuring 2.8 cm × 2.3 cm × 1.9 cm; there were no signs of hydronephrosis. Serum calcium, urate and parathyroid hormone levels were within normal limits. The patient was begun on intravenous ceftazidime to sterilize the urine. Cystoscopy revealed no anatomical abnormalities of the urethra or bladder. The bladder mucosa was mildly inflamed and the bladder wall was slightly thickened. The 11.34 g calculus was removed and sent for analysis. Results revealed 50% magnesium ammonium phosphate hexahydrate (struvite) and 50% carbonate apatite.

Determining the etiology and management of urolithiasis in children is ideally performed by obtaining the stone. Unfortunately, the urine metabolic profile is often the only information available. Table 1 outlines the four most common types of calculi. In our case, before cystoscopy and stone analysis, it was unclear whether the child first developed a stone that then served as a nidus for infection or if he had a long-standing infection predisposing him to stone formation. The predominance of struvite in the stone on analysis indicates that the latter is more likely. A urethral abnormality causing urinary stasis, which could precipitate both stone formation and infection, is plausible, but in our case this was not supported by the findings on cystoscopy. Fifty per cent of children with urolithiasis have metabolic predispositions (as supported by the positive family history in our case), while only 4% are caused by infection (1). Our case was unusual in that the calculus was localized to the bladder, which occurs in less than 10% of North American children with urolithiasis (2). In fact, bladder calculi in children are usually the result of anatomical or functional abnormalities, such as bladder diverticulae or neurogenic bladder (3), both of which were unlikely in this case given the results of the cystoscopy and neurological examination.

Struvite stones are also known as triple phosphate or infection stones; these are commonly mixed with carbonate apatite. Struvite stones are almost always the result of long-standing urinary tract infection with urease-producing bacteria, which include Proteus species (most common), Ureaplasma species, Klebsiella species, Staphylococcus species, Providencia species, Pseudomonas species and Morganella species. Neither E coli nor Enterococcus species are associated with struvite stone formation. These bacteria were cultured in our patient's urine either due to contamination during urine collection or independent colonization of the urinary tract, having utilized the pre-existing stone as a nidus for infection.

Because many types of stones are radiolucent, x-ray and ultrasound are often not sufficiently sensitive to detect them. A computed tomography scan of the abdomen and pelvis without contrast is often the imaging that is required to visualize a stone in the kidney, ureter or bladder. Identification of the type of stone is sometimes suggested by the patient's condition, such as uric acid stones in a patient with Lesch-Nyhan disease. However, stone analysis is required for accurate diagnosis.

Because struvite stones are the result of infection, sterilization of the urine and removal of the stone should remedy the problem. However, many individuals with urinary tract infections never develop urolithiasis. This suggests that some children may be predisposed to stone formation. Up to 30% of children with struvite stones also have metabolic abnormalities (4). The metabolic abnormalities for which our patient should be evaluated as an outpatient include hypercalciuria, hyperoxaluria, hypocitraturia, hyperuricosuria and cystinuria. These are best assessed when the patient has been on a regular diet with normal fluid intake. Two consecutive 24 h urine collections must be analyzed for sodium, calcium, urate, oxalate, citrate, creatinine and cystine (2,5). Arterial blood gases and chemistry panels should be drawn to assess the patient's acid-base status. A repeat urine culture should also be ordered to ensure that the urine has not been recolonized by residual stone particles. If any metabolic abnormalities are detected, other family members should be tested. Many of these conditions are inherited, and if known, stone formation can be prevented.

Treatment for struvite stones depends on their size and degree of urinary tract obstruction. As a general principle, the stones must be eliminated and the urine sterilized (6). If there is an anatomical abnormality contributing to the formation of stones, it must also be corrected. Surgical removal is often necessary because these stones can become quite large. Stones can also be passed through the urine after they are fragmented by various procedures, including shock wave lithotripsy for stones less than 1 cm, percutaneous nephrolithotomy for proximal stones and stones greater than 2 cm, and ureteroscopy for distal stones (7). Medical treatment can include long-term antibiotic therapy, especially if residual stone fragments remain. Urease inhibitors (acetohydroxaminic acid and hydroxyurea) can be used to prevent growth of existing stones and development of new ones. However, these medications have serious toxicities that must be considered (5). Because this child had a solitary stone that was easily accessible, surgical resection and antibiotics were the only interventions necessary.

CLINICAL PEARLS

• Once a urinary calculus has been identified, treatment first depends on whether it is causing an obstruction. The patient's urine should be strained for stone fragments and sent for analysis to help determine the underlying etiology.

• All children with urolithiasis should be evaluated for an underlying metabolic condition. Ideally, this screening should be performed six weeks after passing a stone, once the child has resumed normal food and fluid intake (5).

• If a metabolic condition is identified, certain pharmaceutical and dietary measures can be implemented to prevent future calculus formation.

• Because bladder stones are so rare, this child should also have received further evaluation for functional and/or anatomical anomalies, including urodynamic studies and/or a voiding cystourethrogram. Unfortunately, this patient did not keep his clinic appointment and was lost to follow-up.

REFERENCES