Educational review: role of the pediatric nephrologists in the work-up and management of kidney stones

A case of diffuse kidney hyperechogenicity in early childhood associated with biallelic PKHD1 variants

BACKGROUND

Nephrocalcinosis (NC) is characterized by an excessive accumulation of calcium deposits in the kidneys. In children, it is often incidentally discovered with an uncertain prognosis.

CASE-DIAGNOSIS/TREATMENT

A 3-month-old girl suspected to have a milk protein allergy underwent an ultrasound that revealed increased echogenicity in the kidney pyramids suggestive of medullary NC. At the age of 18 months, imaging findings revealed not only hyperechogenicity in the medulla but also in the cortex. Over the course of a long follow-up, her kidneys maintained size within the upper limits but showed an increase by age 7. Genetic analysis identified PKHD1 variants, which required structural predictive tools to guide clinical diagnosis. Until the age of 7, her kidney function has remained intact; however, her prognosis is uncertain.

CONCLUSIONS

NC in newborns is a rare condition, but its incidence is rising. Recurrent urinary infections or kidney stones may lead to kidney failure. A proactive approach in sporadic NC enables an early diagnosis to orientate clinical supervision and facilitates counseling to support family planning decisions.

In focus: perplexing increase of urinary stone disease in children, adolescent and young adult women and its economic impact

Background

Urinary stone disease (USD) historically has affected older men, but studies suggest recent increases in women, leading to a near identical sex incidence ratio. USD incidence has doubled every 10 years, with disproportionate increases amongst children, adolescent, and young adult (AYA) women. USD stone composition in women is frequently apatite (calcium phosphate), which forms in a higher urine pH, low urinary citrate, and an abundance of urinary uric acid, while men produce more calcium oxalate stones. The reasons for this epidemiological trend are unknown.

Methods

This perspective presents the extent of USD with data from a Canadian Province and a North American institution, explanations for these findings and offers potential solutions to decrease this trend. We describe the economic impact of USD.

Findings

There was a significant increase of 46% in overall surgical interventions for USD in Ontario. The incidence rose from 47.0/100,000 in 2002 to 68.7/100,000 population in 2016. In a single United States institution, the overall USD annual unique patient count rose from 10,612 to 17,706 from 2015 to 2019, and the proportion of women with USD was much higher than expected. In the 10-17-year-old patients, 50.1% were girls; with 57.5% in the 18-34 age group and 53.6% in the 35-44 age group. The roles of obesity, diet, hormones, environmental factors, infections, and antibiotics, as well as the economic impact, are discussed.

Interpretation

We confirm the significant increase in USD among women. We offer potential explanations for this sex disparity, including microbiological and pathophysiological aspects. We also outline innovative solutions - that may require steps beyond typical preventive and treatment recommendations.

How to define and assess the clinically significant causes of hematuria in childhood

Given the wide diversity of causes of hematuria, ranging from simple urinary tract infections with rapid recovery to severe glomerulonephritis with fast decline in kidney function, it is essential to recognize the underlying disease. The first objective of the assessment is to determine whether the cause of the hematuria is medically significant. The combination of hematuria with proteinuria, the presence of hypertension, or worsening kidney function can represent signs of progressive kidney disease. Differentiating the various causes of hematuria is often simple and obvious based on the clinical signs and gross appearance of the urine. However, in some instances, additional non-invasive investigations, such as ultrasound imaging, urinary red cell morphology, measurement of calcium and other solutes in the urine, evaluation of kidney function, and protein excretion, are needed to elucidate the nature of the hematuria. Taking a detailed family history can help in establishing the underlying cause in cases of familial hematuria. On the other hand, the decision to perform a kidney biopsy in children with asymptomatic hematuria remains a challenging issue for clinicians. Ultimately, the frequency of diagnosis of glomerular involvement causing hematuria may depend on the threshold for performing a kidney biopsy. The following review will focus on the diagnostics of hematuria, starting with difficulties regarding its definition, followed by various means to differentiate between urinary, glomerular, and other causes, and finally reviewing the most common diseases that, due to their frequency or their effect on kidney function, present a diagnostic challenge in everyday practice.

Urinary KIM-1 is not correlated with gestational age among 5-year-old children born prematurely

Background

Preterm birth is associated with decreased nephron endowment. Currently, there is no reliable non-invasive biomarker to identify or monitor decreased nephron number in at-risk patients. Urinary Kidney Injury Molecule-1 (KIM-1) is a biomarker of acute and chronic renal injury. We measured urinary KIM-1 among a wide array of other potential biomarkers.

Methods

We conducted an ambispective cohort study of 5-years-old children born prematurely and healthy controls identified from city schools. Detailed anthropometrics, renal ultrasound dimensions, and biochemical parameters were measured. Urinary KIM-1 was measured using Luminex® technology. Age independent z-scores were calculated and compared. Spearman correlations were used for estimating the association between measures and KIM-1.

Results

We enrolled 129 children, 97 (75.2%) born pre-term and 32 (24.8%) healthy controls born at full-term. Pre-term patients had significantly lower weight and body surface area than controls. Pre-term patients and controls did not differ in current age, sex, race, height, blood pressure, urinary sodium, fractional sodium excretion, serum creatinine and estimated GFR. All spearman correlation between KIM-1 and gestational age, renal and serum measurements were weak without statistical significance.

Conclusion

In 5-year-old children born prematurely, KIM-1 was not correlated with gestational age. Further prospective studies need to confirm this finding.

Scoping review of recent evidence on the management of pediatric urolithiasis: summary of meta-analyses, systematic reviews and relevant randomized controlled trials

This scoping review aimed to evaluate and summarize the recent 10 year pediatric urolithiasis literature with a particular focus on systematic reviews, randomized-controlled trials (RCT) and meta-analysis. The systematic literature search performed on September 1, 2021, restricted to the recent 10 years, focused on pediatric urolithiasis that are RCTs, meta-analysis and systematic reviews. The summarized literature included etiology, diagnostics, medical and surgical management. GRADE criteria are used to evaluate and standardize the reporting of evidence quality. A total of 33 relevant articles were included. The recent high-level studies included topics of genetic and diet association with pediatric stone formation, diagnostic assessment, medical management intervention including medical dissolution and expulsion therapy. The study extended to include the efficacy and safety of extracorporeal lithotripsy, percutaneous nephrolithotomy and retrograde intrarenal surgery. However, evidence quality was ranked "very-low" or "low". Based on the GRADE criteria downgrading of the quality level was due to heterogeneity and low precision. A majority of the RCTs were categorized as having a "high" to "uncertain" risk of bias. The relevant RCTs, meta-analyses and systematic reviews within the past decade are of low quality. Consequently, the research provided no clear evidence-based recommendations for managing pediatric urolithiasis. More rigorous research and high-quality studies are needed to determine the best practices.

Computational simulation of the flow dynamic field in a porous ureteric stent

Ureteric stents are employed clinically to manage urinary obstructions or other pathological conditions. Stents made of porous and biodegradable materials have gained increasing interest, because of their excellent biocompatibility and the potential for overcoming the so-called ‘forgotten stent syndrome’. However, there is very limited characterisation of their flow dynamic performance. In this study, a CFD model of the occluded and unoccluded urinary tract was developed to investigate the urinary flow dynamics in the presence of a porous ureteric stent. With increasing the permeability of the porous material (i.e., from 10⁻¹⁸ to 10⁻¹⁰ m²) both the total mass flow rate through the ureter and the average fluid velocity within the stent increased. In the unoccluded ureter, the total mass flow rate increased of 7.7% when a porous stent with permeability of 10⁻¹⁰ m² was employed instead of an unporous stent. Drainage performance further improved in the presence of a ureteral occlusion, with the porous stent resulting in 10.2% greater mass flow rate compared to the unporous stent. Findings from this study provide fundamental insights into the flow performance of porous ureteric stents, with potential utility in the development pipeline of these medical devices.

External validation of efficacy and reliability of different retrograde intrarenal surgery (RIRS) scoring systems for pediatric nephrolithiasis

INTRODUCTION

Retrograde Intrarenal Surgery (RIRS) is one of minimally invasive procedures for pediatric upper urinary stones. However, a RIRS predictive system for children to evaluate postoperative stone free rate (SFR) is still unavailable.

OBJECTIVE

The aim of this study is to validate the efficacy and reliability of different RIRS scoring systems for children.

STUDY DESIGN

We collected clinical data of 137 pediatric patients treated with RIRS in our center between 2014 and 2021. All the predictors were acquired by preoperative non-contrast CT or CT urography. Receiver Operative Curve (ROC) and Area Under Curve (AUC) were showed to compare the predictive power of different models.

RESULTS

A total of 162 RIRS procedures were performed for these 137 pediatric patients. Median surgical duration, irrigation volume and hospitalization were 30 (20, 40) min, 500 (300, 1000) ml and 6 (4, 7) days, respectively. Overall SFR and complication rate was 79.6% (129/162) and 29.2% (40/137), respectively. Significant difference was detected between non-stone free group and stone free group in terms of stone complexity (p < 0.001), cumulative stone sizes [2.3 (2.0, 3.5) cm vs. 1.5 (1.0, 2.0) cm, p < 0.001], RUS groups (p < 0.001), S-ReSC groups (p < 0.001) and RIRS nomogram score [10 (8, 12) vs. 23 (18, 25), p < 0.001]. Among them, RIRS nomogram presented with the maximum AUC values in comparison with the other two systems (RUS: 0.944 vs. 0.874, p = 0.001; S-ReSC: 0.944 vs. 0.808, p < 0.001).

DISCUSSION

We reported the largest sample size of pediatric patients treated with RIRS in our center. Similar with previous studies, RIRS is an efficacious and safe option for pediatric patients. RIRS nomogram showed the best predictive outcome due to the inclusion of multiple parameters, but an innovative predictive system based on pediatric clinical data is warranted in the future.

CONCLUSION

Among the three scoring systems, RIRS nomogram showed the most optimal predictive power of postoperative SFR for pediatric patients.

Animal, Human, and 23Na MRI Imaging Evidence for the Negative Impact of High Dietary Salt in Children

PURPOSE OF THE REVIEW

Conditions typically prevalent in adults such as hypertension, kidney stones, osteoporosis, and chronic kidney disease are increasing among adolescents and young adults (AYA). The purpose of this review is to describe the association of these conditions to a high salt diet among pediatric patients.

RECENT FINDINGS

We present animal, human, and 23Na MRI evidence associated with the negative impact of high dietary salt in children. Special focus is placed on novel 23Na MRI imaging which reveals the important concept of a third compartment for sodium storage in soft tissue. Finally, we make recommendations on who should not be on a low salt diet.

SUMMARY

A high salt intake predisposes children and AYA to considerable morbidity. We exhort the reader to engage in advocacy efforts to curve the incidence and prevalence of high salt-related life-limiting conditions.

The microbiome in urinary tract infections in children - an update

PURPOSE OF REVIEW

Urinary tract infection (UTI) is one of the most common pediatric infections worldwide. Recently introduced 16S rRNA sequencing allows detailed identification of bacteria involved in UTI on a species-based level. The urogenital microbiome in children is scarcely investigated, with underlying conditions differing from adults. Improvement in diagnostic and therapeutic approaches can help to minimize unnecessary antibiotic treatments, thereby protecting the physiological microbiome.

RECENT FINDINGS

Healthy bladders of children display a distinct microbiome than those of adults. UTI is characterized by changes in bacterial composition, with a high prevalence of Enterobacterales. There is a correlation between bacterial species and the pH of the urine, so a characteristic age-related pathogen pattern can be found due to the acidic urine in infants and more alkaline urine in older children. Recently, new methods were proposed to overcome the suboptimal diagnostic performance of urine cultures and urine dipstick test. This allows precise treatment decisions and helps to prevent chronification of UTI, related voiding dysfunctions and renal scaring, systemic abiosis, and the development of antibiotic resistance.

SUMMARY

Uropathogens involved in UTIs in children should be identified with precision to allow targeted therapeutic decisions. This can also help preventing the destruction of the microbiome homeostasis, which could result in a life-long dysbiosis. New treatment approaches and recolonization with probiotics are necessary due to increasing intrinsic antibiotic resistance of bacteria.

Current update and future directions on gut microbiome and nephrolithiasis

The incidence of nephrolithiasis is increasing worldwide. Understanding how gut microbiome influences oxalate homeostasis has the potential to offer new strategies to prevent nephrolithiasis. The literature was reviewed to gather the evidence on the association between gut microbiome, hyperoxaluria and nephrolithiasis, and to identify the therapeutic interventions focused on the gut microbiome that could decrease hyperoxaluria and prevent nephrolithiasis. Gut microbiome is constituted by a plethora of microbiota including Oxalobacter formigenes (Oxf) and lactobacilli. Oxf can degrade dietary oxalate and induce enteral oxalate secretion. Animal studies suggested an association between oral Oxf supplementation and a decrease in hyperoxaluria. However, human studies have showed inconsistent results. Oral supplementation of lactobacilli did not show benefit in decreasing the hyperoxaluria. Antibiotic exposure, by affecting the gut microbiome, has been associated with an increase in nephrolithiasis. In vivo studies suggest fecal transplantation as a potential treatment option for reducing nephrolithiasis, but needs further evaluation in clinical studies. The current evidence suggests an association between gut microbiome and nephrolithiasis. However, the strategies focused on modulating gut microbiome for decreasing hyperoxaluria and preventing nephrolithiasis need further research. Judicious use of antibiotics in those predisposed to nephrolithiasis offers a preventative strategy for decreasing nephrolithiasis.

Evaluation of a child with suspected nephrolithiasis

PURPOSE OF REVIEW

As the incidence of nephrolithiasis in children doubles every 10 years it is becoming a common disease associated with significant morbidity along with considerable economic burden worldwide. The aim of this review is to summarize current data on the epidemiology and causes of renal stones in children and to provide a frame for the first clinical evaluation of a child with suspected nephrolithiasis.

RECENT FINDINGS

Dietary and environmental factors are the driving force of changing epidemiology. Diagnosis should be based on medical history, presenting signs, examination, first laboratory and radiological workup. Ultrasound should be the initial diagnostic imaging performed in pediatric patients while low-dose computed tomography is rarely necessary for management. Metabolic factors including hypercalciuria, hypocitraturia, low fluid intake as well as specific genetic diseases should be explored after the resolution of initial signs and symptoms.

SUMMARY

Appropriate initial evaluation, imaging technique, identification of risk factors and other abnormalities are essential for early diagnosis and prevention of stone-related morbidity in children with suspected nephrolithiasis.