Abnormal Circadian Rhythm of Diuresis or Nocturnal Polyuria in a Subgroup of Children With Enuresis and Hypercalciuria is Related to Increased Sodium Retention During Daytime

First uninterrupted sleep period in children and adolescents with nocturnal enuresis: Added value in diagnosis and follow-up during therapy

BACKGROUND

The first uninterrupted sleep period (FUSP, time up to the first episode of enuresis/nocturia after falling asleep) is a frequently investigated parameter in adults with nocturia, as it correlates with quality of life. However, it has not been included in pediatric enuresis studies.

AIM

Investigate FUSP, circadian renal water and sodium handling, as well as sleep quality before and after desmopressin therapy in enuresis.

MATERIALS AND METHODS

We conducted a post hoc analysis of a prospective study in 30 treatment-naïve children with enuresis who underwent a video-polysomnography and a 24-h urine concentration profile before and after 6 months of desmopressin therapy. We analyzed FUSP, periodic limb movements in sleep (PLMS), and arousal indexes and their correlations with the urinary parameters.

RESULTS

Sixteen children with a mean age of 10.9 ± 3.1 years had full registrations and were included in this subanalysis. After therapy, FUSP was significantly longer (p < 0.001), and the PLMS index was lower (p = 0.023). Significant differences in the circadian rhythm of diuresis (night/day diuresis, p = 0.041), nocturnal urinary osmolality (p = 0.009), and creatinine (p = 0.001) were found, demonstrating the increase of urinary concentration overnight by desmopressin, as well as a significant antidiuretic effect (diuresis [p = 0.013] and diuresis rate (p = 0.008). There was no correlation between the difference of FUSP, PLMS index, and urinary parameters. Nevertheless, despite this study being underpowered, there are indications of a correlation between nocturnal diuresis and diuresis rate.

RESULTS

Our results support the need for further research regarding FUSP in children with enuresis, in accordance with nocturia studies in adults, as this parameter could be valuable in the follow-up and evaluation of therapeutic strategies for enuresis.

Circadian rhythm of water and solute excretion in nocturnal enuresis

BACKGROUND

Nocturnal polyuria (NP) due to a suppressed vasopressin circadian rhythm is a well-documented pathogenetic mechanism in enuresis, mainly studied in monosymptomatic enuresis. A substantial percentage of patients do not respond to desmopressin. This suggests that NP may not only be related to vasopressin, but that other kidney components play a role. Solute handling and osmotic excretion have been investigated in the past, especially in refractory patients. Nevertheless, data in treatment-naïve populations with information on timing overnight are sparse. This study aims to investigate the diuresis and solute excretion in treatment-naïve patients with or without NP, with emphasis on circadian rhythms.

METHODS

Retrospective analysis of 403 treatment-naïve children 5-18 years with severe enuresis (> 8 nights/2 weeks). Circadian rhythms were evaluated by a 24-h urine collection in 8 timed portions (4 day, 4 nighttime) at in-home settings. Urine volume, osmolality, and creatinine were measured. Patients were subdivided into three groups according to nocturnal diuresis (ND) and Expected Bladder Capacity (EBCage) ratio: (a) < 100%, (b) 100-129%, (c) > 130%.

RESULTS

All groups maintained circadian rhythm for diuresis and diuresis rates. Patients with higher ND (100-129% and > 130% EBCage) had higher daytime volumes and less pronounced circadian rhythm. In the ND group > 130% EBCage, the ND rate was higher during the first night collection and osmotic excretion was significantly higher overnight.

CONCLUSIONS

Overall 24-h fluid intake (reflected by 24-h diuresis) and nutritional intake (24-h osmotic excretion) might play a role in enuresis. Increased diuresis rate early in the night can be important in some patients, whereas the total night volume can be important in others. A higher resolution version of the Graphical abstract is available as Supplementary Information.

Management of treatment-resistant nocturnal enuresis

Nocturnal enuresis is defined as intermittent urinary incontinence during sleep in children 5 years of age and older, occurring at least once a month for at least 3 months. In Japan, pediatricians who do not specialize in nocturnal enuresis have become more proactive in treating the condition since 2016, when the guidelines for treating it were revised for the first time in 12 years. For monosymptomatic nocturnal enuresis, the first step is lifestyle guidance, with a focus on the restriction of fluid intake at night; however, if lifestyle guidance does not decrease the frequency of nocturnal enuresis, aggressive treatment should be added. The first choice of aggressive treatment is oral desmopressin, an antidiuretic hormone preparation, or alarm therapy. However, there remain patients whose wet nights do not decrease with oral desmopressin or alarm therapy. In such cases, it is necessary to reconfirm the method of desmopressin administration and check for factors that may decrease the efficacy of desmopressin. If alarm therapy does not increase the number of dry nights, it is possible that the patient is fundamentally unsuitable for alarm therapy. If dry nights do not increase with oral desmopressin or alarm therapy, the next treatment strategy should be considered immediately to keep the patient motivated for treatment.

High daily salt intake had a negative impact on how well nocturnal enuresis treatment worked on children aged 7-10 years

AIM

We investigated whether the daily salt intake of children with nocturnal enuresis influenced their response to 1-desamino-8-D-arginine vasopressin therapy.

METHODS

This study comprised 129 children (67.4% boys) with a median age of 9.2 years (range 7.2-10.4) with monosymptomatic nocturnal enuresis who were seen at Kansai Medical University Hospital, Osaka, Japan, from 2013 to 2017. Urinary sodium concentrations were determined using a spot urine test, and the children were divided into appropriate (n = 55) and excessive salt intake (n = 74) groups based on Japanese Government guidelines. After a month of therapy, the treatment responses were compared for 39 and 50 children, respectively.

RESULTS

There were no significant differences in the urea nitrogen-to-creatinine or calcium-to-creatinine ratios in the two groups. However, the excessive salt intake group showed a significantly reduced treatment response to the appropriate salt intake group. In addition, the excessive and appropriate salt intake groups showed median efficacy ratios of 8.2% and 21.8%, respectively, based on intention-to-treat analysis (P = 0.029) and 12.0% and 30.8% based on per-protocol analysis (P = 0.029).

CONCLUSION

High daily salt intake significantly reduced the efficacy of ddavp therapy for nocturnal enuresis and consumption should be controlled during treatment.

Circadian regulation of renal function

The kidneys regulate many vital functions that require precise control throughout the day. These functions, such as maintaining sodium balance or regulating arterial pressure, rely on an intrinsic clock mechanism that was commonly believed to be controlled by the central nervous system. Mounting evidence in recent years has unveiled previously underappreciated depth of influence by circadian rhythms and clock genes on renal function, at the molecular and physiological level, independent of other external factors. The impact of circadian rhythms in the kidney also affects individuals from a clinical standpoint, as the loss of rhythmic activity or clock gene expression have been documented in various cardiovascular diseases. Fortunately, the prognostic value of examining circadian rhythms may prove useful in determining the progression of a kidney-related disease, and chronotherapy is a clinical intervention that requires consideration of circadian and diurnal rhythms in the kidney. In this review, we discuss evidence of circadian regulation in the kidney from basic and clinical research in order to provide a foundation on which a great deal of future research is needed to expand our understanding of circadian relevant biology.

The pathophysiology of monosymptomatic nocturnal enuresis with special emphasis on the circadian rhythm of renal physiology

Nocturnal polyuria in monosymptomatic nocturnal enuresis (MNE) has so far mainly been attributed to a disturbed circadian rhythm of renal water handling. Low vasopressin levels overnight correlate with absent maximal concentrating activity, resulting in an increased nocturnal diuresis with low urinary osmolality. Therefore, treatment with desmopressin is a rational choice. Unfortunately, 20 to 60 % of children with monosymptomatic enuresis are desmopressin-resistant. There is increasing evidence that other disturbed circadian rhythms might play a role in nocturnal polyuria. This review focuses on renal aspects in the pathophysiology of nocturnal polyuria in MNE, with special emphasis on circadian rhythms. Articles related to renal circadian rhythms and enuresis were searched through the PubMed library with the goal of providing a concise review.

CONCLUSION

Nocturnal polyuria can only partially be explained by blunted circadian rhythm of vasopressin secretion. Other alterations in the intrinsic renal circadian clock system also seem to be involved, especially in desmopressin-resistant enuresis.

WHAT IS KNOWN

• Disturbance in the circadian rhythm of arginine vasopressin secretion is related to nocturnal polyuria in children with enuresis. • Desmopressin is recommended as a treatment for monosymptomatic nocturnal enuresis, working as a vasopressin analogue acting on V2 receptors in the collecting ducts of the kidney. What is New: • Other renal circadian rhythms might play a role in nocturnal polyuria, especially in desmopressin-resistant case.

Nocturnal enuresis and nocturia, differences and similarities - lessons to learn?

This review highlights the current views on and differences and similarities between nocturnal enuresis (NE) in children and nocturia in adults, which might be a guidance to elucidate the missing links in our knowledge. In both conditions, a genetic factor is suspected. Reduced bladder capacity and nocturnal polyuria are the main underlying lower urinary tract-related conditions. There is a link with sleep disorders, although it is not clear whether this is a cause or consequence. Physical and mental health are comprised in both conditions, however, in different ways. In NE, constipation and attention deficit disorder are the most important comorbidities and the effect on mental health and quality of life is mainly through the negative impact on self-esteem. In nocturia, cardiovascular disease and fall injuries are important comorbidities, mainly affecting the older nocturia population; personal distress and depression are consequences of the related poor sleep quality. For both conditions, treatment is often inadequate and a more individualized approach seems to be necessary. The main difference between NE and nocturia seems to be the difference in arousal to bladder stimuli, suggesting that sleep characteristics might be a key factor in these conditions.

Non-dipping phenomenon in children with monosymptomatic nocturnal enuresis

PURPOSE

Monosymptomatic nocturnal enuresis is a common disorder seen in childhood, and many factors play a role in its etiopathology to varying degrees. The aim of our study was to investigate the possible association between nocturnal enuresis and 24-h blood pressure profiles of enuretic children.

METHODS

A total of 45 children ranging in age from 6 to 15 years with monosymptomatic nocturnal enuresis and 22 age-matched healthy controls were enrolled in our study. The blood pressure measurement was made at 30-min intervals during a 24-h period via an ambulatory blood pressure measurement device. Both groups underwent medical tests that included a complete blood count, blood biochemistry profile, urinalysis and blood renin-aldosterone levels, and all study subjects received an abdominal ultrasound.

RESULTS

Statistically significant high nocturnal blood pressure levels were observed in our patients with monosymptomatic nocturnal enuresis compared with the control group (p < 0.05). The mean values of the day-to-night difference (dipping) in the systolic and diastolic blood pressure of the patients were significantly lower than those of control group (p < 0.05).

CONCLUSION

Nocturnal enuresis should not only be accepted as a urinary system disorder. Possible systemic causative factors have to be examined, especially in patients that are resistant to first-line therapy. Based on the results of our study, we deduce that one of the factors that plays a role in the pathogenesis of enuresis nocturna is a non-dipping blood pressure profile (the "non-dipping" phenomenon).

Treatment for nocturnal enuresis: the current state in Japan

Nocturnal enuresis is common problem in children with a prevalence as high as 20% among children aged 5. Though nocturnal enuresis does not directly impose imminent danger to a patient's life, children with enuresis and their parents can be psychologically suffering in day-to-day life, including in school activities. Therefore, it is important to provide an explanation regarding the cause of nocturnal enuresis, how to approach the disorder, the course, and the outlook leading to the planned treatment. The cause of enuresis is considered to be a mismatch between nocturnal diuresis and nocturnal bladder capacity, nocturnal polyuria due to a lack of circadian change in antidiuretic hormones, and a developmental delay in the voiding mechanisms. Therefore, patients can be classified as the type associated with a large amount of urine at night (polyuria type), the type that is associated with a functionally small bladder capacity (bladder type), the type associated with both the aforementioned (mixed type), or the type that does not fall under any of these (normal type). Based on this logic, although the International Children's Continence Society has issued the standardization document, in which the enuresis alarm and desmopressin therapy are recommended as the first line treatment, a different tack has been taken in Japan, where the therapeutic strategy is plotted depending on the type of enuresis; pharmacotherapy for enuretic children aged 6 years or older includes desmopressin acetate for polyuria type, anticholinergic agents for bladder type, and a combination of these agents for mixed type.

Oral lyophylizate formulation of desmopressin: superior pharmacodynamics compared to tablet due to low food interaction

PURPOSE

Desmopressin is a standard treatment for monosymptomatic nocturnal enuresis. Different formulations are promoted as bioequivalent, although these claims are not supported by comparative pharmacodynamic data in children. Food interaction is known to influence the bioavailability of desmopressin. We compared the pharmacodynamics of the 2 most frequently used desmopressin formulations, tablet and lyophilizate, with a standardized meal, allowing extrapolation to clinical reality, where the interval between evening meal and medication intake is limited for school-age children. We hypothesized there would be a faster pharmacodynamic response, and greater concentrating and antidiuretic activity for the fast dissolving (melt) formulation compared to the tablet with simultaneous food intake.

MATERIALS AND METHODS

Two tests were performed on separate days in identical standardized conditions, starting with a 15 ml/kg water load. After achieving maximal diluting capacity a standardized meal was administered, followed by desmopressin tablet (t test) or melt (M-test). Diuresis rate and urinary osmolality were measured hourly. Paired data from 4 girls and 15 boys with a mean age of 12.1 years were obtained.

RESULTS

In the early response phase more than 25% of patients had a higher diuresis rate with tablet vs melt formulation, reaching statistical significance in the plateau phase (urine collected at hours 3 to 5, p <0.02) and in duration of action (urine collected at hours 5 to 8, p <0.005). For desmopressin melt smaller standard deviations in diuresis rate were remarkable. Concentrating capacity demonstrated no significant differences between formulations in the early response phase, in contrast to the plateau phase (p <0.036) and duration of action (p <0.001).

CONCLUSIONS

With meal combination desmopressin melt formulation has a superior pharmacodynamic profile to tablet, making it more suitable for the younger age group with a limited interval between meal and drug administration.

Molecular clock is involved in predictive circadian adjustment of renal function

Renal excretion of water and major electrolytes exhibits a significant circadian rhythm. This functional periodicity is believed to result, at least in part, from circadian changes in secretion/reabsorption capacities of the distal nephron and collecting ducts. Here, we studied the molecular mechanisms underlying circadian rhythms in the distal nephron segments, i.e., distal convoluted tubule (DCT) and connecting tubule (CNT) and the cortical collecting duct (CCD). Temporal expression analysis performed on microdissected mouse DCT/CNT or CCD revealed a marked circadian rhythmicity in the expression of a large number of genes crucially involved in various homeostatic functions of the kidney. This analysis also revealed that both DCT/CNT and CCD possess an intrinsic circadian timing system characterized by robust oscillations in the expression of circadian core clock genes (clock, bma11, npas2, per, cry, nr1d1) and clock-controlled Par bZip transcriptional factors dbp, hlf, and tef. The clock knockout mice or mice devoid of dbp/hlf/tef (triple knockout) exhibit significant changes in renal expression of several key regulators of water or sodium balance (vasopressin V2 receptor, aquaporin-2, aquaporin-4, alphaENaC). Functionally, the loss of clock leads to a complex phenotype characterized by partial diabetes insipidus, dysregulation of sodium excretion rhythms, and a significant decrease in blood pressure. Collectively, this study uncovers a major role of molecular clock in renal function.

Evidence of partial anti-enuretic response related to poor pharmacodynamic effects of desmopressin nasal spray

PURPOSE

Desmopressin is an evidence-based medicine level I, category A therapy for monosymptomatic nocturnal enuresis. However, in up to 40% of patients only partial desmopressin response is obtained. While the poor pharmacokinetic characteristics of the different available formulations may have a role in apparent therapy resistance, there are limited data available to support this theory. We sought to identify pharmacodynamic factors involved in partial desmopressin response or desmopressin resistance in children with monosymptomatic nocturnal enuresis, with special emphasis on concentrating performance, and time to reach and duration of maximal urine concentration.

MATERIALS AND METHODS

We evaluated 64 children with monosymptomatic nocturnal enuresis and proved nocturnal polyuria lacking full response to desmopressin treatment. The study involved 2 separate home based test days (A and B), each consisting of 9 timed urine collections starting in the evening 1 hour before desmopressin administration and continuing for 16 hours following desmopressin administration. Test A was done during fluid restriction, and test B was done during an oral fluid load.

RESULTS

Under fluid restriction 16 patients failed to achieve urine concentration greater than 850 mOsmol/l at the midnight collection following desmopressin administration. After an oral fluid load given at the start of the test the majority of patients failed to reach maximal concentration of urine as voided during hydropenia, and 45 patients failed to regain appropriate dilution of urine even when an oral water load of 15 ml/kg (urine osmolality less than 750 mOsmol/l) was given in the morning at the end of the test. This finding is suggestive of a prolonged duration of action of the drug.

CONCLUSIONS

Pharmacodynamic tests reveal a suboptimal effect of desmopressin on urine concentration in a significant percentage of patients, which worsens when fluid is not restricted before desmopressin administration. Also the time to reach maximal antidiuretic effect and the duration of pharmacodynamic action show a wide range, requiring individualization of mode and time of administration. Our data demonstrate that a simple pharmacodynamic test as described may give important information on time of dosing, duration of action and influence of oral fluid intake, allowing individualization of therapy. Data also reveal that desmopressin should be administered at least 1 hour before bedtime, and that in case of therapy resistance a longer interval, up to 2 hours, might further reduce diuresis rate in the early night. Because of the documented prolonged action of desmopressin in some patients, increasing the dose without performing pharmacodynamic testing is no longer acceptable.

Physiology and pathophysiology of the vasopressin-regulated renal water reabsorption

To prevent dehydration, terrestrial animals and humans have developed a sensitive and versatile system to maintain their water homeostasis. In states of hypernatremia or hypovolemia, the antidiuretic hormone vasopressin (AVP) is released from the pituitary and binds its type-2 receptor in renal principal cells. This triggers an intracellular cAMP signaling cascade, which phosphorylates aquaporin-2 (AQP2) and targets the channel to the apical plasma membrane. Driven by an osmotic gradient, pro-urinary water then passes the membrane through AQP2 and leaves the cell on the basolateral side via AQP3 and AQP4 water channels. When water homeostasis is restored, AVP levels decline, and AQP2 is internalized from the plasma membrane, leaving the plasma membrane watertight again. The action of AVP is counterbalanced by several hormones like prostaglandin E2, bradykinin, dopamine, endothelin-1, acetylcholine, epidermal growth factor, and purines. Moreover, AQP2 is strongly involved in the pathophysiology of disorders characterized by renal concentrating defects, as well as conditions associated with severe water retention. This review focuses on our recent increase in understanding of the molecular mechanisms underlying AVP-regulated renal water transport in both health and disease.

Pitfalls in studies of children with monosymptomatic nocturnal enuresis

In this issue Ferrara et al. present an important placebo-controlled, three-arm, double-blind, double-dummy, study on the treatment of nocturnal enuresis, demonstrating that homotoxicology is superior to placebo but less effective than desmopressin. Nocturnal enuresis is a disease with a heterogeneous aetiology and complex pathophysiology. The fact that different therapies may result in a wide range of responses is, therefore, not surprising. Differences in success rate can, therefore, be largely attributed to selection bias in the sub-populations. This consideration must be taken into account for every study design, to avoid premature interpretation of the results. Positive results in a paper are only not subject for discussion if both methodology and study population fulfil the highest standards, because negative results are not likely to be reported. Several points of weakness are present in the majority of studies, such as (a) inappropriate subtyping of the patients (terminology) or (b) epidemiological data, (c) insufficient documentation of patients' characteristics, (d) lack of plausible explanation as to why the placebo effect might be absent, (e) the heterogeneity of the severity of bedwetting. All these may lead to false positive and/or false negative results. In this commentary we try to tackle these different issues which might be relevant for the interpretation even of placebo-controlled studies like that of Ferrara et al.

Nocturnal polyuria is related to 24-hour diuresis and osmotic excretion in an enuresis population referred to a tertiary center

PURPOSE

Primary nocturnal enuresis is a heterogeneous disorder, causing a mismatch between overnight diuresis volume and functional bladder capacity. Despite increasing insights in pathogenesis, lack of efficacy of the available treatments is a major problem. We evaluated characteristics of bladder volume and diuresis rate in patients with nocturnal enuresis referred to a tertiary enuresis center.

MATERIALS AND METHODS

Noninvasive screening including maximal voided volume, 24-hour circadian rhythm of diuresis and osmotic excretion from 1,000 consecutive patients.

RESULTS

Of the patients referred as having monosymptomatic nocturnal enuresis 32% were subsequently classified as having nonmonosymptomatic nocturnal enuresis. Differences in bladder volume and nocturnal diuresis characteristics between the monosymptomatic nocturnal enuresis and nonmonosymptomatic nocturnal enuresis groups were minimal.

CONCLUSIONS

The most common observation is a nocturnal diuresis volume greater than maximal voided volume, which in both groups can be caused by nocturnal polyuria or small bladder volume for patient age. The most striking observation is that the positive correlation between nocturnal diuresis volume rate and nocturnal osmotic excretion and 24-hour fluid intake is significantly higher than with the inversed urinary osmolality overnight, which is not only unexpected based on the theory of the primary suppression of vasopressin levels overnight, but also points to a more important role for nutritional and fluid intake than accepted, if not in the primary pathogenesis, then at least in therapy resistance.