Hypercalciuria in pediatric patients with ureteropelvic junction obstruction is of genetic origin

Forming a stone in pelviureteric junction obstruction: Cause or effect?

OBJECTIVES

To investigate a possible causal relationship for stone formation in pelviureteric junction obstruction and to outline management options.

MATERIALS AND METHODS

A literature search and evidence synthesis was conducted via electronic databases in the English language using the key words pelviureteric junction obstruction; urolithiasis; hyperoxaluria; laparoscopic pyeloplasty; flexible nephroscopy; percutaneous nephrolithotomy, alone or in combination. Relevant articles were analysed to extract conclusions.

RESULTS

Concomitant pelviureteric junction obstruction (PUJO) and renal lithiasis has been reported only scarcely in the literature. Although PUJO has been extensively studied throughout the years, the presence of calculi in such a patient has not received equal attention and there is still doubt surrounding the pathophysiology and global management.

CONCLUSIONS

Metabolic risk factors appear to play an important role, enough to justify metabolic evaluation in these patients. Urinary stasis and infection are well known factors predisposing to lithiasis and contribute to some extent. The choice for treatment is not always straightforward. Management should be tailored according to degree of obstruction, renal function, patient symptoms and stone size. Simultaneous treatment is feasible with the aid of minimally invasive operative techniques and laparoscopy in particular.

[Unilateral renal agenesis. New arguments about the genetic relationship between kidney malformations and urolithiasis]

BACKGROUND

In few previous works, it has been reported that hypercalciuria is associated with some types of CAKUT, namely ureteropelvic junction obstruction, vesicoureteral reflux or simple renal cysts. In addition, one higher prevalence of hypercalciuria and/or urolithiasis has been described in their family members compared to the general population. This study was carried out to find out whether children with unilateral renal agenesis (URA) have these features previously described in other CAKUT types.

METHODS

In a descriptive and multicenter study we studied the prevalence of hypercalciuria, hypocitraturia and urolithiasis in 67 children (43 males and 24 females) with URA and their families.

RESULTS

The two metabolic anomalies that promote stone formation were observed in 26 children (38.8%), distributed as follows: hypercalciuria in 16, hypocitraturia in 9, and both hypercalciuria and hypocitraturia in 1. Eight children (11.9%) suffered renal colic during follow-up. Familial history of urolithiasis was found in 42/67 children (62.7%): in 12 of the first-degree relatives, in 15 of the second degree relatives and in 15 patients both in the first-degree as in their second degree relatives. In contrast, in historic control group, only in 28.1% of families at least one member had urolithiasis.

CONCLUSION

Our results show that the prevalence of hypercalciuria and/or hypocitraturia is greater in pediatric patients with URA than in the general population. Likewise, the prevalence of urolithiasis in the families of these children is also higher than that in the general population.

Unilateral hypercalciuria: a stealth culprit in recurrent ipsilateral urolithiasis in children

PURPOSE

Hypercalciuria is a risk factor for nephrolithiasis. We hypothesized that children with recurrent stones in 1 but not both kidneys and a normal 24-hour bladder urine calcium-to-creatinine ratio might exhibit isolated hypercalciuria of the affected kidney.

MATERIALS AND METHODS

Patients 18 years or younger with symptomatic urolithiasis who had undergone ureteroscopic stone removal were included. All subjects underwent 24-hour bladder urinalysis. Subjects with an increased urine calcium-to-creatinine ratio from the 24-hour urine collection were excluded. The 4 subject cohorts defined were 1) single stone episode in 1 kidney, 2) single stone episode in both kidneys, 3) recurrent stone episodes on 1 side and 4) recurrent stone episodes on both sides. All urine collections were obtained at ureteroscopy. Urine was obtained from the bladder and from the renal pelvis of the kidney forming the stone. Spot urine calcium-to-creatinine ratio was determined from these samples.

RESULTS

A total of 329 patients were included. Nine of 74 subjects (12%) with recurrent stone episodes on 1 side had increased spot urine calcium-to-creatinine ratio from the affected kidney. No patients in the other cohorts had increased spot urine calcium-to-creatinine ratio. Patients who formed recurrent stones in 1 kidney had increased spot urine calcium-to-creatinine ratio in the affected kidney vs other stone formers (ANOVA p <0.001).

CONCLUSIONS

Unilateral hypercalciuria can occur in children with normal calcium levels in bladder urine. Unilateral hypercalciuria should be considered as a risk factor for nephrolithiasis in children with recurrent stone episodes in 1 kidney only.

Pediatric urolithiasis in Taiwan: a nationwide study, 1997-2006

OBJECTIVE

To investigate the prevalence, incidence, associated risk factors, and treatment of pediatric urolithiasis in Taiwan.

METHODS

The present study used a subset of the National Health Insurance Research Database, known as the Longitudinal Health Insurance Database 2005, which contains the data for all paid medical benefit claims from 1997 to 2006 for a subset of 1 million beneficiaries randomly drawn from the population of 22.72 million individuals during any part of the calendar year 2005. Our analysis included the data of all newly diagnosed pediatric patients with an "International Classification of Disease, 9th revision," diagnosis of urolithiasis from 1997 through 2006.

RESULTS

A total of 1679 pediatric subjects who had newly diagnosed urolithiasis without a previous attack were identified from 1997 to 2006 as the study sample. Of the 1679 patients, 808 were boys (48.1%) and 871 were girls (51.9%). The incidence rate of urolithiasis in 2005 was 0.047%. The peak age of pediatric stone occurrence in the study sample was 15-18 years (49.6%). The most common associated disease was urinary tract infection (34.1% of all subjects). The occurrence rate of pediatric urolithiasis correlated significantly with the urbanization level of the residence and geographic area.

CONCLUSION

Using a nationwide, population-based study provides important clinical and epidemiologic information regarding pediatric urolithiasis. Additional studies are warranted to determine the effect of geographic area and urbanization level on the occurrence of pediatric stone disease.

Urinary calcium and uric acid excretion in children with vesicoureteral reflux

Urolithiasis is relatively common in children, and identifiable predisposing factors for stone formation, including metabolic and structural derangements, can be established in most cases. Vesicoureteral reflux (VUR) is a common cause of kidney stone formation. The pathophysiological mechanism of urolithiasis in reflux is related to urinary tract infection and urinary stasis, both of which promote urinary crystal formation, but metabolic causes, such as crystallurias (mostly hypercalciuria), may also be involved in this process. However, few studies on urinary calcium and uric acid excretion in children with VUR have been conducted. We have studied the frequency of hypercalciuria and hyperuricosuria in children with VUR and compared the results with those from a control group. The VUR group comprised 108 children with VUR (19 boys, 89 girls; age range 3 months to 12 years), and the control group comprised 110 healthy children without any history of reflux or urinary tract infection (30 boys, 80 girls; age range 2 months to 12 years). Fasting urine was analyzed for the calcium/creatinine (Ca/Cr) and uric acid/creatinine (UA/Cr) ratios. Hypercalciuria was more frequently diagnosed in the VUR patients than in the control group (21.3 vs. 3.6%; P = 0.0001). Significant differences between the two groups were also found for the mean Ca/Cr and UA/Cr ratios (P = 0.0001 and P = 0.0001, respectively). No differences were found in the urinary Ca/Cr or UA/Cr ratios related to VUR grading or unilateral/bilateral VUR in the patient group, with the exception of those for hypercalciuria and mild VUR (P = 0.03). The association of urinary stones and microlithiasis in the VUR group was 29.6%. Our results demonstrate that the frequency of hypercalciuria and hyperuricosuria was higher in pediatric patients with VUR than in healthy children. Knowing this relationship, preventive and therapeutic interventions for stone formation in VUR could be greatly expanded.

Derivation of a melamine oral reference dose (RfD) and drinking-water total allowable concentration

Due to its high nitrogen content, melamine has been used to adulterate food to increase apparent protein content. In 2008, thousands of Chinese infants consumed reconstituted formula derived from melamine-adulterated milk. Urinary-tract stones (comprised of melamine and uric acid) accumulated in some victims and lead to acute renal failure or death. Premature infants and children (<2 yr) have an increased susceptibility to ingested melamine. Due to incomplete reporting, the human data were inadequate to identify a no-observed-adverse-effect level (NOAEL) for melamine-induced pediatric urolithiasis. Urolithiasis, urinary bladder cystitis, and ulcerations were observed in F344 rats after subchronic or chronic ingestion of melamine at > or =72 mg/kg-d. Bladder epithelial damage was followed by epithelial hyperplasia that progressed to bladder papillomas and carcinomas in male but not female F344 rats or male or female B6C3F1 mice. Short-term assays suggest, at best, weak genotoxic activity, and kinetic data show that melamine is not metabolized. Since reliable exposure information was lacking from the clinical reports, an oral reference dose (RfD) based on urolithiasis in male rats after 13 wk of continuous melamine ingestion was calculated as a 10% benchmark dose (38 mg/kg-d). Incorporation of 10-fold interspecies and intraspecies (for the increased susceptibility of infants) uncertainty factors and a threefold database uncertainty factor (for the lack of immunological, neurological and reproduction toxicity data) yields an oral RfD of 0.13 mg/kg-d. Assuming the 70-kg adult consumes 2 L of drinking water daily, a total allowable concentration of 0.9 mg/L (900 microg/L) was calculated for melamine in drinking water.

Pediatric urolithiasis

PURPOSE OF REVIEW

We review the recent literature on pediatric urolithiasis and present up-to-date findings on epidemiology, diagnosis, and medical and surgical management.

RECENT FINDINGS

There are surprisingly few reliable data on pediatric urolithiasis incidence, but widespread anecdotal and single-center reports suggest that more children with stones are being seen. The contamination of Chinese infant formula with melamine caused urolithiasis and other renal problems in hundreds of thousands of infants in the region, underlining the role of environmental factors in urolithiasis. Efforts continue to determine normal metabolic parameters in children, but have been hampered by variations among regions, races, and ethnicities. The Bonn Risk Index may prove to be a useful tool for assessing risk of urolithiasis in children. Children with recurrent urolithiasis are more likely to have detectable metabolic abnormalities. Surgical approaches to urolithiasis in children continue to evolve, with robotic-assisted laparoscopy being perhaps the most significant new technique. Finally, clinicians and radiologists must be aware of the potential for dextranomer/hyaluronic acid (Deflux) implants to mimic distal ureteral stones on computed tomography (CT) scan.

SUMMARY

Pediatric urolithiasis is an expanding field, due in part to the apparent increase in cases. Research continues, seeking to refine the appropriate diagnostic and therapeutic approaches in these unfortunate children.

[Urolithiasis and ureteropelvic junction obstruction]

The review of the literature about ureteropelvic junction (UPJ) obstruction and concomitant renal stone has highlighted two major aspects. First, urinary stagnation due to UPJ obstruction is frequently associated with metabolic disorders such as hypercalciuria. Second, results of laparoscopic pyeloplasty are at least as good as those of open surgery but with the advantages of a minimal access approach. Exploration of the renal cavity with the laparoscope or a fibroscope allows to treat in the same time a concomitant renal calculi.