Medical treatment of cystinuria: critical reappraisal of long-term results

Medical management of kidney stones: AUA guideline

PURPOSE

The purpose of this guideline is to provide a clinical framework for the diagnosis, prevention and follow-up of adult patients with kidney stones based on the best available published literature.

MATERIALS AND METHODS

The primary source of evidence for this guideline was the systematic review conducted by the Agency for Healthcare Research and Quality on recurrent nephrolithiasis in adults. To augment and broaden the body of evidence in the AHRQ report, the AUA conducted supplementary searches for articles published from 2007 through 2012 that were systematically reviewed using a methodology developed a priori. In total, these sources yielded 46 studies that were used to form evidence-based guideline statements. In the absence of sufficient evidence, additional statements were developed as Clinical Principles and Expert Opinions.

RESULTS

Guideline statements were created to inform clinicians regarding the use of a screening evaluation for first-time and recurrent stone formers, the appropriate initiation of a metabolic evaluation in select patients and recommendations for the initiation and follow-up of medication and/or dietary measures in specific patients.

CONCLUSIONS

A variety of medications and dietary measures have been evaluated with greater or less rigor for their efficacy in reducing recurrence rates in stone formers. The guideline statements offered in this document provide a simple, evidence-based approach to identify high-risk or interested stone-forming patients for whom medical and dietary therapy based on metabolic testing and close follow-up is likely to be effective in reducing stone recurrence.

Therapy modifies cystine kidney stones at the macroscopic scale. Do such alterations exist at the mesoscopic and nanometre scale?

With an incidence of 1:7000 births, cystinuria, the most frequent cause of stone formation among genetic diseases, represents a major medical problem. Twenty-five cystine stones randomly selected from cystinuric patients were investigated. From a crystallographic point of view, cystine stones are composed of micrometre size crystallites, which are made up of an aggregation of nanocrystals. Through scanning electron microscopy, the morphology and size of the crystallites have been described, while the size of the nanocrystals was investigated by means of powder neutron diffraction. Powder neutron diffraction analysis and/or scanning electron microscopy examination of cystine stones provide evidence that usual alkalinization by sodium bicarbonate associated with high diuresis significantly reduces the size of both nanocrystals and crystallites, while for other treatments, including alkalinizing drugs and thiol derivatives, the data suggest mainly changes in the topology of crystallites. Alkalinization with sodium bicarbonate affects cystine kidney stones at the mesoscopic and nanoscopic scales, while other medical treatments only alter their surface. Such an approach may help to assess the interaction between drugs and cystine stones in cystinuric patients.

Cystinuria-a urologist's perspective

Cystinuria is a genetic disease that leads to frequent formation of stones. In patients with recurrent stone formation, particularly patients <30 years old or those who have siblings with stone disease, urologists should maintain a high index of suspicion of the diagnosis of cystinuria. Patients with cystinuria require frequent follow-up and a multidisciplinary approach to diagnosis, prevention and management. Patients have reported success in preventing stone episodes by maintaining dietary changes using a tailored review from a specialist dietician. For patients who do not respond to conservative lifestyle measures, medical therapy to alkalinize urine and thiol-binding drugs can help. A pre-emptive approach to the surgical management of cystine stones is recommended by treating smaller stones with minimally invasive techniques before they enlarge to a size that makes management difficult. However, a multimodal approach can be required for larger complex stones. Current cystinuria research is focused on methods of monitoring disease activity, novel drug therapies and genotype-phenotype studies. The future of research is collaboration at a national and international level, facilitated by groups such as the Rare Kidney Stone Consortium and the UK Registry of Rare Kidney Diseases.

The effect of prophylactic treatment with Shohl's solution in children with cystinuria

OBJECTIVE

To investigate the effect of prophylactic treatment with Shohl's solution on the rates of stone recurrence in paediatric patients with cystinuria.

PATIENTS AND METHODS

Between June 2007 and October 2011, 185 patients aged 16 years and younger whose stones had been completely removed by percutaneous nephrolithotomy (PCNL) were assessed for metabolic risk factors. Seventeen (9%) patients with positive cyanide-nitroprusside tests (CNT) and cystine stones enrolled in this study, and a Shohl's solution was used for alkalinisation. The patients were followed up for a mean period of two years for stone recurrence.

RESULTS

Of the patients, 10 (59%) were male, and 7 (41%) were female (p = 0.13). Twelve patients (70.5%) continued to receive medical prophylaxis regularly, whereas 5 (29.5%) patients did not. The mean pre-treatment and post-treatment urinary pH values were 5.8 ± 0.5 (5-7) and 7.5 ± 0.4 (6.5-8), respectively (p < 0.001). The pre-treatment and post-treatment specific gravities of the urine were 1021.5 ± 5.4 (1010-1030) and 1006 ± 2.3 (1004-1015), respectively (p < 0.001). The rates of recurrence were 16.6% among those who continued prophylaxis and 100% among those who did not receive prophylaxis (p = 0.001). The most common combination of metabolic anomalies was cystinuria and hypocitraturia (p < 0.001).

CONCLUSIONS

This study demonstrated that detailed clinical and laboratory evaluations should be performed for all children with cystine stone disease, and, appropriate prophylactic treatment should be recommended to prevent the reformation of stones.

Cystinuria: mechanisms and management

Cystinuria is a relatively uncommon cause of pediatric stone disease, but has significant morbidity if not properly controlled because of its significant stone recurrence rate. Cystinuria is caused by the inability of the renal tubules to reabsorb filtered cystine, which is poorly soluble at a typical urine pH <7. Although many advances have been made in the understanding of the genetic and physiological basis of cystinuria, the cornerstones of treatment still involve stone prevention with dietary measures and pharmacological therapy, coupled with surgical interventions for stone removal. Pharmacological treatments can carry significant side effects that must be monitored and can limit therapy as well as impede compliance. Most patients will require surgical intervention for stone removal, although compliance with prevention strategies reduces the need for intervention.

Clinical review. Kidney stones 2012: pathogenesis, diagnosis, and management

CONTEXT

The pathogenetic mechanisms of kidney stone formation are complex and involve both metabolic and environmental risk factors. Over the past decade, major advances have been made in the understanding of the pathogenesis, diagnosis, and treatment of kidney stone disease.

EVIDENCE ACQUISITION AND SYNTHESIS

Both original and review articles were found via PubMed search reporting on pathophysiology, diagnosis, and management of kidney stones. These resources were integrated with the authors' knowledge of the field.

CONCLUSION

Nephrolithiasis remains a major economic and health burden worldwide. Nephrolithiasis is considered a systemic disorder associated with chronic kidney disease, bone loss and fractures, increased risk of coronary artery disease, hypertension, type 2 diabetes mellitus, and the metabolic syndrome. Further understanding of the pathophysiological link between nephrolithiasis and these systemic disorders is necessary for the development of new therapeutic options.

Approach to the Adult Kidney Stone Former

Nephrolithiasis is a prevalent and costly condition with high recurrence rate. A medical evaluation to identify abnormalities responsible for nephrolithiasis and guide subsequent therapy has been advocated to reduce the risk of stone recurrence. The evaluation of kidney stone formers generally comprises an extensive medical history to identify metabolic, environmental, dietary and/or genetic factors contributing to stone formation. Imaging studies are utilized to evaluate and follow stone burden. Laboratory studies including stone composition analysis and serum and urinary chemistries are commonly obtained to further assess for any underlying systemic disorders, to detect environmental and metabolic processes contributing to stone disease, and to guide initial and follow-up dietary and pharmacological therapy. The nature and extent of such an evaluation is discussed in this review article.

Spectrophotometric determination of N-acetyl-L-cysteine and N-(2-mercaptopropionyl)-glycine in pharmaceutical preparations

A simple spectrophotometric method for the determination of N-acetyl-L-cysteine (NAC) and N-(2-mercaptopropionyl)glycine (MPG) in pharmaceutical preparations was developed, validated, and used. The proposed equilibrium method is based on a coupled two-step redox and complexation reaction. In the first step, Fe(III) is reduced to Fe(II) by NAC or MPG. Subsequently, Fe(II) is complexed with 2,4,6-tripyridyl-s-triazine (TPTZ). Several analytical parameters of the method were optimized for NAC and MPG analysis in the concentration range from 1.0 μM to 100.0 μM. Regression analysis of the calibration data showed a good correlation coefficient (0.9999). The detection limit of the method was 0.14 μM for NAC and 0.13 μM for MPG. The method was successfully applied to quantify NAC and MPG in pharmaceutical preparations. No interferences were observed from common pharmaceutical excipients.

Pharmacotherapy of urolithiasis: evidence from clinical trials

Urolithiasis is a worldwide problem with significant health and economic burdens. Medical therapy that alters the course of stone disease has enormous medical and financial impact. Urolithiasis is a final manifestation of a broad range of etiologies and pathogenesis. The modest progress in understanding the pathophysiology has hampered successful development of targeted therapy. Current regimens are based mostly on rational alteration of urinary biochemistry and physical chemistry to lower the risk of precipitation. In terms of pharmacotherapy, there are drugs to successfully improve hypercalciuria, hypocitraturia, aciduria, hyperuricosuria, and hypercystinuria. These agents have been proven to be effective in randomized controlled trials in improving urinary biochemical and physicochemical risk factors, as well as clinical outcomes. Although our current regimens have clearly improved the management and lives of stone formers, there are still clearly identifiable immense voids in the knowledge of pathophysiology of stone disease that can be filled with combined basic science and clinical studies.

Penicillamine therapy for pediatric cystinuria: experience from a cohort of American children

PURPOSE

Cystinuria, an inherited defect of dibasic amino acid transport, causes accumulation of urinary cystine and cystine urolithiasis. In adults penicillamine reduces stone formation but has a high incidence of dose limiting toxicity. We evaluated the effects of penicillamine in preventing stone formation and with respect to toxicity in our cystinuria cohort at a pediatric biochemical genetics clinic.

MATERIALS AND METHODS

We reviewed the charts of all 11 children with cystinuria treated at our clinic using a gradual dose escalation of penicillamine. Mean +/- SD patient age at diagnosis was 5.8 +/- 4.3 years (range 1.2 to 12). We tracked urinary cystine concentration before and after initiation of treatment, penicillamine side effects and incidence of new stones during maintenance therapy.

RESULTS

During the gradual escalation of penicillamine to the target dose none of the 11 patients experienced toxicity and all had improved urinary cystine concentration (mean +/- SD percent reduction 54% +/- 25%, range 5% to 81%). We followed the patients for a total of 1,203 months (mean +/- SD 109 +/- 73 months, range 41 to 221), periodically assessing urinary cystine concentration, urine protein content, complete blood count, blood urea nitrogen, creatinine and liver function. During this time only 2 patients experienced significant side effects and no patient had stones or stone crises while compliant with treatment.

CONCLUSIONS

In our cohort penicillamine was well tolerated after gradual initiation and it reduced urinary cystine concentration. Long-term compliance with the medication appeared to protect patients from acute stone crises.

Cystinuria

Cystinuria is an inherited disorder characterized by the impaired reabsorption of cystine in the proximal tubule of the nephron and the gastrointestinal epithelium. The only clinically significant manifestation is recurrent nephrolithiasis secondary to the poor solubility of cystine in urine. Although cystinuria is a relatively common disorder, it accounts for no more than 1% of all urinary tract stones. Thus far, mutations in 2 genes, SLC3A1 and SLC7A9, have been identified as being responsible for most cases of cystinuria by encoding defective subunits of the cystine transporter. With the discovery of mutated genes, the classification of patients with cystinuria has been changed from one based on phenotypes (I, II, III) to one based on the affected genes (I and non-type I; or A and B). Most often this classification can be used without gene sequencing by determining whether the affected individual's parents have abnormal urinary cystine excretion. Clinically, insoluble cystine precipitates into hexagonal crystals that can coalesce into larger, recurrent calculi. Prevention of stone formation is the primary goal of management and includes hydration, dietary restriction of salt and animal protein, urinary alkalinization, and cystine-binding thiol drugs.

Acetazolamide is an effective adjunct for urinary alkalization in patients with uric acid and cystine stone formation recalcitrant to potassium citrate

OBJECTIVES

Acetazolamide has been proposed as a treatment adjunct for patients with cystine and uric acid stone formation recalcitrant to standard alkalization therapy. We evaluated the effect of acetazolamide in urinary alkalization in patients with uric acid and cystine stone formation recalcitrant to potassium citrate alone.

METHODS

An institutional review board-approved, retrospective chart review identified 12 patients at 2 sites who had been prescribed acetazolamide as a treatment adjunct to potassium citrate for uric acid or cystine stones from 1997 to 2007. We evaluated the urine studies, metabolic evaluations, surgical interventions, and stone recurrence or growth.

RESULTS

The mean follow-up was 46.1 months (range 11-86). Ten patients (83%) were categorized as compliant. Of the 2 patients excluded from the study, 1 was noncompliant with the medication, and the other was lost to follow-up. Of the 10 patients who were compliant with the treatment, 5 (50%) developed adverse effects from the medication requiring discontinuation. Of the remaining 5 patients (50%) who tolerated the medication and remained compliant, 3 (60%) were stone free at a mean follow-up of 42 months. Two patients continued to form stones, including one who developed calcification of an existing uric acid stone. Both patients required surgical intervention. The mean urinary pH before treatment was 5.9 (range 5-7) and after treatment was 7.2 (range 6.5-8.5; P = .001).

CONCLUSIONS

Acetazolamide was effective in increasing the urinary pH in patients with uric acid and cystine stone formation who were already taking potassium citrate. Caution must be taken when prescribing acetazolamide, because it could be poorly tolerated and can induce calcium phosphate stone formation.

[Inherited monogenic kidney stone diseases: recent diagnostic and therapeutic advances]

Hereditary monogenic kidney stone diseases are rare diseases, since they account for nearly 2% of nephrolithiasis cases in adults and 10% in children. Most of them are severe, because they frequently are associated with nephrocalcinosis and lead to progressive impairment of renal function unless an early and appropriate etiologic treatment is instituted. Unfortunately, treatment is often lacking or started too late since they are often misdiagnosed or overlooked. The present review reports the genotypic and phenotypic characteristics of monogenic nephrolithiases, with special emphasis on the recent advances in the field of diagnosis and therapeutics. Monogenic stone diseases will be classified into three groups according to their mechanism: (1) inborn errors of the metabolism of oxalate (primary hyperoxalurias), uric acid (hereditary hyperuricemias) or other purines (2,8-dihydroxyadeninuria), which, in addition to stone formation, result in crystal deposition in the renal parenchyma; (2) congenital tubulopathies affecting the convoluted proximal tubule (such as Dent's disease, Lowe syndrome or hypophosphatemic rickets), the thick ascending limb of Henlé's loop (such as familial hypomagnesemia and Bartter's syndromes) or the distal past of the nephron (congenital distal tubular acidosis with or without hearing loss), which are frequently associated with nephrocalcinosis, phosphatic stones and extensive tubulointerstitial fibrosis; (3) cystinuria, an isolated defect in tubular reabsorption of cystine and dibasic aminoacids, which results only in the formation of stones but requires a cumbersome treatment. Analysis of stones appears of crucial value for the early diagnosis of these diseases, as in several of them the morphology and composition of stones is specific. In other cases, especially if nephrocalcinosis, phosphatic stones or proteinuria are present, the evaluation of blood and urine chemistry, especially with regard to calcium, phosphate and magnesium, is the key of diagnosis. Search for mutations is now increasingly performed in as much as genetic counselling is important for the detection of heterozygotes in autosomic recessive diseases and of carrier women in X-linked diseases. In conclusion, better awareness to the rare monogenic forms of nephrolithiasis and/or nephrocalcinosis should allow early diagnosis and treatment which are needed to prevent or substantially delay progression of end-stage renal disease. Analysis of every first stone both in children and in adults should never be neglected, in order to early detect unusual forms of nephrolithiasis requiring laboratory evaluation and deep etiologic treatment.

Cystinuria in children and young adults: success of monitoring free-cystine urine levels

Medical treatment of cystinuria is often disappointing. Patients undergo frequent surgery, which is often followed by early relapse. The aim of our study was to evaluate the efficacy of medical treatment of cystinuria, to prevent formation or to reduce the numbers and dimensions of renal stones. Twenty cystinuric patients were treated with a combined approach, including cystine-binding drugs. Free and bound urine cystine levels were measured every 4 months. Drug dosage was adjusted to maintain free urine cystine level below 100 micromol/mmol creatinine. Eighteen patients completed the study; detection of new stones was reduced from 0.28 per year to 0.03 per year, and, in six patients, the numbers and dimensions of pre-existing renal stones were reduced. Surgery was required in one subject, and no relapse was observed 12 months afterwards. The dosage required to achieve target levels was closely correlated with patient body weight: older children required a lower dose. Medical management of cystinuria is feasible. The treatment must be personalised in children, as the amount of drug required is strictly dependent on body size.

[Evidence-based pharmacological metaphylaxis of stone disease]

Approximately one-fourth of urolithiasis patients are at high risk for recurrent stone formation or severe metabolic disturbances. These patients need specific metaphylaxis for effective stone prevention, adjusted to their individual metabolic risk. Recent recommendations for the pharmacological treatment of stone diseases are summarized in this article. For the different treatment options, evidence from the literature was assessed. In addition, a follow-up concept for pharmacologically treated high-risk stone formers is discussed.

Slc7a9knockout mouse is a good cystinuria model for antilithiasic pharmacological studies

Cystinuria is a hereditary disorder caused by a defect in the apical membrane transport system for cystine and dibasic amino acids in renal proximal tubules and intestine, resulting in recurrent urolithiasis. Mutations in SLC3A1 and SLC7A9 genes, that codify for rBAT/b0,+AT transporter subunits, cause type A and B cystinuria, respectively. In humans, cystinuria treatment is based on the prevention of calculi formation and its dissolution or breakage. Persistent calculi are treated with thiols [i.e., d-penicillamine (DP) and mercaptopropionylglycine (MPG)] for cystine solubilization. We have developed a new protocol with DP to validate our Slc7a9 knockout mouse model for the study of the therapeutic effect of drugs in the treatment of cystine lithiasis. We performed a 5-wk treatment of individually caged lithiasic mutant mice with a previously tested DP dose. To appraise the evolution of lithiasis throughout the treatment a noninvasive indirect method of calculi quantification was developed: calculi mass was quantified by densitometry of X-ray images from cystinuric mice before and after treatment. Urine was collected in metabolic cage experiments to quantify amino acids in DP-treated and nontreated, nonlithiasic mutant mice. We found significant differences between DP-treated and nontreated knockout mice in calculi size and in urinary cystine excretion. Histopathological analysis showed that globally nontreated mutant mice had more severe and diffuse urinary system damage than DP-treated mice. Our results validate the use of this mouse model for testing the efficacy of potential new drugs against cystinuria.

Management of Cystinuria

Cystinuria is a monogenic disorder in which there is a transepithelial transport defect of di-basic amino acids, including cystine, ornithine, lysine, and arginine (COLA). This results in diminished reabsorption of these amino acids in both the intestine and renal proximal tubule. This article describes the disorder, reviews the mechanisms of normal COLA renal transport, and summarizes issues related to the disorder, such as the role of mutations, associated diseases, clinical manifestations, therapies, the renal impact, and handling of pediatric patients.

Cystine calculi: challenging group of stones

Cystinuria is an autosomal recessive disorder in renal tubular and intestinal transport of dibasic amino acids, which results in increased urinary excretion of cystine, ornithine, lysine and arginine. It affects 1 in 20 000 people and is caused by a defect in the rBAT gene on chromosome 2. Development of urinary tract cystine calculi is the only clinical manifestation of this disease. Owing to recurrent episodes of stone formation, these patients require a multi-modal approach to management. The role of medical management and minimally invasive surgery was reviewed for the treatment of cystinuria.

Urological intervention in patients with cystinuria is decreased with medical compliance

PURPOSE

Theoretically patients with cystinuria compliant with medical treatment should undergo fewer surgical procedures than those noncompliant with treatment. We describe a single urologist's experience (SYN) with the effects of medical management on the number of surgical interventions required in patients with cystinuria treated at our metabolic stone clinic (MSC).

MATERIALS AND METHODS

The records of 20 patients with cystine stones seen at our MSC (mean followup of 42.5 months) were evaluated. The number of surgical interventions (endourology or open surgery) during followup were recorded as surgical events. Patients were placed into a compliant or noncompliant category based on their attendance record at scheduled appointments at our MSC and whether they adhered to the prescribed medical regimen by report. Patients were classified in an active disease category if recent imaging revealed a clinically significant stone burden greater than 3 mm. Statistical analysis of the number of surgical events for stone-free patients compliant with treatment versus noncompliant was conducted (Student's t test).

RESULTS

Of the 20 patients 11 were categorized as compliant and 9 as noncompliant. Of the compliant patients the average number of surgical events was 1.0 per patient versus 4.0 in the noncompliant group (p <0.05). Of the 11 compliant patients 8 (73%) were stone-free compared to 3 (33%) in the noncompliant group.

CONCLUSIONS

The majority of our patients with cystinuria compliant with treatment underwent a significantly fewer number of surgical procedures per year than those noncompliant with treatment. Active medical management in patients with cystinuria compliant with treatment decreases the incidence of surgical interventions.

Reduced renal function and benefits of treatment in cystinuria vs other forms of nephrolithiasis

A significant study from the USA compares cystine stone formers and routine stone formers; the former group had a higher requirement for therapeutic procedures, but this was less if they took chelating agents, although remaining higher than in the latter group. Other interesting findings are also presented.

OBJECTIVE

First, to compare two types of stone formers (SF), those with cystinuria and those without, for effects of treatments for stones, as cystinuria leads to recurrent stones that are difficult to fragment with shock-wave lithotripsy, and there is disagreement about the efficacy of current treatments. Second, to compare these two groups with respect to blood pressure (BP) and renal function, as cystine stones may be associated with more morbidity than are routine stones.

PATIENTS AND METHODS

Fifty-two cystinuric patients (cystine SF) entering our programme since 1970 were compared with 3215 SF without cystinuria (routine SF), of whom 114 had a single functioning kidney (routine SF + nephrectomy). All patients had three 24-h urine and blood samples taken to determine the risk of stones before their first clinic visit; these studies were repeated after therapy was initiated, and at regular intervals to monitor therapy. Cystine was measured in the urine samples of the cystine SF. All stone-related procedures were recorded, and BP measured at clinic visits. Creatinine clearances (CCr) were calculated from each set of serum and urine values. Cystine supersaturation (SS) was directly measured in 16 urine samples collected before treatment and 13 afterward.

RESULTS

Patients were treated with increased fluid intake, potassium alkali and chelating agents such as alpha-mercapto-propionyl-glycine, as needed. The mean (sd) CCr, corrected for age and gender, was significantly lower at entry in cystine SF than in routine SF, at 91 (6) vs 160 (1) L/day, respectively (P < 0.001), and remained so at the last CCr. Neither systolic nor diastolic BP, similarly corrected, differed between the groups, but cystine SF had significantly more procedures, corrected for time at risk, before treatment than did routine SF, at 4.0 (0.4) vs 1.86 (0.06), respectively (P < 0.001); time-adjusted procedures decreased significantly in both groups during treatment, but remained higher in cystine SF, at 0.88 (0.14) vs 0.23 (0.02), respectively, (P < 0.001). Urine volume and pH were significantly higher in cystine SF than in routine SF, both before and during treatment. Cystine SS decreased during treatment, consistent with the increase in urine volume and decline in procedure rates during treatment.

CONCLUSION

Cystine SF have significantly higher procedure rates than routine SF, but procedure rates decline during therapy, although they remain higher than in routine SF. The lower CCr in cystinurics suggests that treatment to prevent stone recurrence and the need for procedures is particularly important, and emphasizes the need for a close follow-up. Use of cystine SS measurements may allow closer monitoring of the effect of treatment on the risk of stone recurrence.

Diagnosis and metaphylaxis of stone disease. Consensus concept of the National Working Committee on Stone Disease for the upcoming German Urolithiasis Guideline

This review draws the recent state of the art in metabolic diagnosis and metaphylaxis of stone disease. It is the basis for the consensus approval with the other medical societies and institutions in Germany involved in the guideline process of the new "Urolithiasis Guideline". The German Working Committee on Stone Disease reviewed critically the current literature in the field of urolithiasis-including the existing German and EAU-Guidelines as well as the Conference Book of the First International Consultation on Stone Disease. As far as possible the references were rated according to the EBM criteria. On this basis the expert group discussed all pathways and statements regarding the management of stone disease. The present review coincides with the consented guideline draft of the German Working Committee on Stone Disease. Occurrence of stone disease in the western world increases seriously. Modern lifestyle, dietary habits and overweight-problems of the affluent societies-emerge to be the important promoters of the "stone-boom" in the new millennium. This even affects children, whose stone prevalence is otherwise significantly less than that of adults. Criteria for the high risk group of stone formers were clearly defined. A diagnostic standard is formulated for the basic and the elaborate metabolic evaluation of a stone patient. Approximately 75% of all stone patients could anticipate stone recurrence with elementary reorientation of their lifestyle and dietary habits, summarized as general metaphylaxis. About 25% of the stone formers require additional pharmacological intervention to normalize their individual biochemical risk, precisely compiled for each stone type as specific metaphylaxis.

Insuffisance rénale terminale d'origine lithiasique : fréquence, causes et prévention

Nephrolithiasis still remains a too frequent - and under-appreciated - cause of end-stage renal disease (ESRD), and this is all the most unfortunate since such an untoward course is now preventable in most cases. Among 1391 patients who started maintenance dialysis at Necker hospital between 1989 and 2000, nephrolithiasis was identified as the cause of ESRD in 45 of them, an overall prevalence of 3.2%. Infection stones accounted for 42.2% of cases, calcium stones for 26.7%, uric acid stones for 17.8% and hereditary diseases for 13.3%. The proportion of nephrolithiasis-associated ESRD declined from 4.7% to 2.2% from the 1989-1991 to the 1998-2000 period, as a result of the decreased incidence of ESRD in patients with infection and calcium nephrolithiasis. Based on our observations and on published reports, it emerges that most cases of nephrolithiasis-associated ESRD were due to sub-optimal management (especially in the case of infection or cystine stones) or to late (or erroneous) etiologic diagnosis, precluding early institution of appropriate therapeutic measures. In particular, several patients with primary hyperoxaluria or 2,8-dihydroxyadeninuria were diagnosed while already on dialysis or after unsuccessful kidney transplantation, due to wrong initial diagnosis. In conclusion, thanks to recent advances in diagnosis and management of stone formers, ESRD should now be prevented in the great majority of patients, at the condition of early etiologic diagnosis based on accurate morphoconstitutional analysis of calculi and metabolic evaluation, and early implementation of appropriate preventive medical treatment.

Liquid chromatography analysis of N-(2-mercaptopropionyl)-glycine in biological samples by ThioGlo 3 derivatization

N-(2-Mercaptopropionyl)-glycine (MPG) is a synthetic aminothiol antioxidant that is used in the treatment of cystinuria, rheumatoid arthritis, liver and skin disorders. Recent studies have shown that MPG can function as a chelating, cardioprotecting and a radioprotecting agent. Several other studies have shown that it may also act as a free radical scavenger because of its thiol group. Thiol-containing compounds have been detected in biological samples by various analytical methods such as spectrophotometric and colorimetric methods. However, these methods require several milliliters of a sample, time-consuming procedures and complicated derivatization steps, as well as having high detection limits. The present study describes a rapid, sensitive and relatively simple method for detecting MPG in biological tissues by using reverse-phase HPLC. With ThioGlo 3 [3H-Naphto[2,1-b] pyran, 9-acetoxy-2-(4-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl) phenyl-3-oxo-)] as the reagent, highly fluorescent derivatives of thiols can be obtained that are suitable for HPLC. MPG is derivatized with ThioGlo 3 and is then detected flourimetrically by reverse phase HPLC using a C18 column as the stationary phase. Acetonitrile: Water (75:25) with acetic acid and phosphoric acid (1 mL/L) is used as the mobile phase (excitation wavelength, 365 nm; emission wavelength, 445 nm). The calibration curve for MPG is linear over a range of 10-2500 nM (r=0.999) and the coefficients of the variation of within-run and between-run precision were found to be 0.3 and 2.1%, respectively. The detection limit was 5.07 nM per 20 microL injection volume. Quantitative relative recovery of MPG in the biological samples (plasma, lung, liver, kidney and brain) ranged from 90+/-5.3 to 106.7+/-9.3 %. Based on these results, we have concluded that this method is suitable for determining MPG in biological samples.

Cystinuria in childhood and adolescence: recommendations for diagnosis, treatment, and follow-up

Cystinuria, an autosomal-recessive disorder of a renal tubular amino acid transporter, is the cause of about 10% of all kidney stones observed in children. Different genetic characteristics are not represented by different phenotypes. The stones are formed of cystine, which is relatively insoluble at the physiological pH of urine. Without any preventive measures, the patients will suffer from recurrent stone formation throughout their life. Even with medical management, long-term outcome is poor due to insufficient efficacy and low patient compliance. Many patients suffer from renal insufficiency as a result of recurrent stone formation and repeated interventions. However, regular follow-up and optimal pharmacotherapy significantly increase stone-free intervals. Medical management is mainly based on hyperhydration and urine alkalinization. Sulfhydryl agents such as tiopronin can be added. Recurrent stone formation necessitates repeated urological interventions. These mostly minimally invasive procedures carry the risk of impairment of renal function. In adults, extracorporeal shockwave lithotripsy (SWL) as well as intracorporeal lithotripsy is often unsuccessful. However, in children SWL shows excellent results for cystine stones. In cases with large stone burden, percutaneous nephrolithotripsy (PNL) or even open surgical nephrolithotomy are preferred. This review discusses the underlying pathogenetic mechanisms and provides guidance for the diagnosis, therapy, and management of cystinuria following the recommendations of the International Cystinuria Consortium and the European Association of Urology.

[Alkaline citrates in urology. A status report]

Alkaline citrates have been used as an efficient therapy in hypocitraturic calcium nephrolithiasis, uric acid lithiasis, cystinuria, and renal tubular acidosis. Furthermore, alkaline citrates are very effective in treating and preventing hyperchloremic metabolic acidosis in patients with urinary diversion. The main physiological effects during urolithiasis therapy have been significant increases in urinary pH, in citrate and potassium, and a decrease in calcium excretion. This paper reviews current indications, therapy modalities, and metaphylactic use reported in the literature and/or recommended by the Deutsche Gesellschaft für Urologie (DGU) and the European Association of Urology (EAU). It is intended to give useful advice for the urologist's daily practice.

[Prevention of nephrolithiasis. Established strategies and new concepts]

During the last 2 decades in Germany, only minor efforts were expended for the prevention of urinary stones. Substantial technical progress simplified the treatment of existing calculi; thus, it was more convenient to treat a new stone than to prevent its recurrence. But times change! In these days of financial squeeze in the medical system, prevention becomes more attractive. Nevertheless, strategies for kidney stone prevention developed. Established concepts for dietary advice were rejected due to the results of new randomized studies. Moreover, new pharmacological substances were introduced for metaphyalxis. The new concepts are feasible for the daily routine. For some treatment modalities in stone prevention, there is valid evidence from the literature, which should encourage us to adopt these modalities in the future. A number of drugs are used as "good common practice" without any proof from a randomized trial. Often prospective and valid studies are not available. The present paper intends to describe the status quo of nephrolithiasis prevention in Germany, focussing on confirmed data and unsolved problems.

Stone clustering of patients with cystine urinary stone formation

OBJECTIVES

To explore the history of symptomatic cystine stone formation. Cystinuria is a genetic defect that may result in the formation of recurrent cystine calculi.

METHODS

Thirty-four patients with cystinuria were retrospectively evaluated for treatment patterns, medical prophylaxis, and renal outcome. Patients were offered a conservative surgical regimen and routine radiographic and laboratory follow-up and were encouraged to use medical prophylaxis. A Poisson regression model was used to analyze the patterns of stone formation.

RESULTS

The mean age at presentation and at last follow-up was 18 and 38 years, respectively. Patients underwent a total of 249 procedures, with an average of 7.3 procedures per patient, including 37% percutaneous nephrolithotomies; 25.7% shock wave lithotripsy procedures; 22.1% ureteroscopies; 12.9% open lithotomies; and 1.6% nephrectomies. In 29% of patients, unilateral surgery only was required. With a conservative treatment regimen, no patient developed renal insufficiency or failure. The overdispersion estimated from the Poisson model was 5.03 (P <0.001) if patients were evaluated from birth to last follow-up and 2.06 (P <0.001) if followed from first presentation to last-follow-up, suggesting a clustering of stone events. Overdispersion was moderately related to increased age (older than 34 years).

CONCLUSIONS

The results of our study showed that patients with cystinuria develop symptomatic calculi in clusters, with a slight predominance of stone formation after the age of 34. The cause of the stone clustering is unclear. Renal function can be preserved with a conservative surgical treatment protocol. Contemporary medical prophylaxis may be ineffective.

Durability of the medical management of cystinuria

PURPOSE

Cystinuria is an autosomal recessive disorder of dibasic amino acid transport in the kidney that leads to an abundance of cystine in the urine. This molecule is poorly soluble in urine and it is prone to crystallization and stone formation at concentrations above 300 mg./l. Medical treatment in these patients has incorporated increasing urine volumes, alkalinization and thiol medications that decrease the availability of free cystine in urine. Despite a reasonable prognosis for reduced stone formation we and others have noted difficulties in patients complying with medical management recommendations. Therefore, we evaluated the durability of treatment success in our patients with cystinuria.

MATERIALS AND METHODS

A retrospective chart review was performed in all patients with cystinuria referred to the comprehensive kidney stone center at our institution for an 8-year period. Medical therapy, stone recurrence rates, compliance with medications and scheduled followup, and the results of metabolic evaluations via 24-hour urine collections were reviewed. The average concentrations of urinary cystine in initial and followup 24-hour samples were compared in patients compliant and noncompliant with medical treatment. In addition, each patient was mailed a 1-page questionnaire to assess the self-perception of medical compliance.

RESULTS

We identified 26 patients with a mean age of 32 years at referral (range 13 to 67) who were followed an average of 38.2 months (range 6 to 83). Females represented 58% of those with cystinuria. Overall compliance with medical recommendations was poor with a short duration of success. Of the 26 patients followed at our stone center only 4 (15%) achieved and maintained therapeutic success, as defined by urine cystine less than 300 mg./l. An additional 11 patients (42%) achieved therapeutic success but subsequently had failure at an average of 16 months (range 6 to 27). Of these patients 7 (64%) regained therapeutic success at an average of 9.4 months (range 4 to 20). Five patients (19%) never achieved therapeutic success, while an additional 6 (23%) failed to present to followup appointments or provide subsequent 24-hour urine studies despite referral to a tertiary care center. Patient self-assessment of medical compliance was uniformly high regardless of physician perceptions or treatment results. CONCLUSIONS The durability of medically treating patients with cystinuria is limited with only a small percent able to achieve and maintain the goal of decreasing cystine below the saturation concentration. Greater physician vigilance in these complicated stone formers is required to achieve successful prophylactic management. Furthermore, these patients require better insight into the own disease to improve compliance.

Cystinuria and other noncalcareous calculi

Urinary stone disease is the only clinical presentation in patients with cystinuria. Two genes have been associated with type I (SLC3A1) and non-type I (SLC7A9) cystinuria and multiple mutations of these genes have been identified. The type I form is completely recessive while the non-type I form is incompletely recessive. Clinically, heterozygotes with type I mutations are silent while heterozygotes with non-type I (types II and III) present with a wide range of urinary cystine levels and some even have symptomatic urolithiasis. Although the exact molecular basis for these differences needs additional investigations, the future of medical management of cystinuria is based on molecular and gene therapy. Minimally invasive surgery using percutaneous and ureteroscopic techniques is the cornerstone of surgical management. Both cystine and struvite calculi can form staghorn configuration with propensity for rapid growth and frequent recurrences after surgical treatment. While urinary alkalinization for cystine calculi is an integral part of medical management, the effect of oral alkalinizing agents is limited because of the high pKa (8.3) of cystine. Chelating agents, therefore, are frequently used to decrease cystine solubility and stone recurrences. Similarly, urinary acidification for struvite calculi may dissolve existing stones and prevent recurrences. However, no effective oral agent is available today. A future challenge will be to introduce reliable oral agents for urinary acidification.

Medical treatment of nephrolithiasis

The medical treatment of nephrolithiasis is aimed in particular at the prevention of relapses, even though in some cases, such as cystine or uric acid lithiasis, the calculi also can be dissolved on site. When the diagnosis and metabolic profile have been performed correctly, medical treatment is effective in a large number of patients. The greatest difficulty is the patient's compliance with the most suitable prevention measures and the frequency of follow-up controls. This compliance can be influenced significantly by the amount of time that the doctor spends to explain the origin of the disease. This article reviews the main methods available for the medical treatment of various nephrolithiasis types, namely water intake, diet, and drugs, supplying the relevant information about the mechanism of action, metabolic consequences, indications, evidence provided from studies, dosage, efficacy, and side-effects. Finally, brief simplified guidelines are given for the medical treatment of stone disease caused by calcium oxalate or calcium phosphate, uric acid, cystine, and struvite.

Medical and surgical therapy of the cystine stone patient

Cystinuria is an inherited defect in renal tubular and intestinal transport of dibasic amino acids that results in elevated urinary excretion of cystine, ornithine, lysine, and arginine. The only clinical manifestation of this disease is the development of urinary tract cystine calculi. Cystinuric patients suffer recurrent stone episodes, requiring an aggressive multi-modal approach to management. This article reviews the results of medical prevention regimens, the role of minimally invasive urologic intervention, and the recent insights into the complex genetic basis for the varied cystinuric phenotypes.