PEDIATRICS Vol. 115 No. 4 April 2005, pp. 956-959 (doi:10.1542/peds.2004-1402)
Primary and Secondary Nocturnal Enuresis: Similarities in Presentation
* Department of Pediatric Urology, University of Oklahoma, Oklahoma City, Oklahoma
Department of Pediatrics, University of Calgary, Calgary, Alberta, Canada
Michigan State University College of Human Medicine, Marquette, Michigan
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Objective. To determine the differences or similarities in the clinical presentation between patients with primary and secondary nocturnal enuresis.
Methods. A total of 170 patients with nocturnal enuresis were assessed at a busy tertiary care pediatric voiding dysfunction clinic at the University of Oklahoma Health Sciences Center. Patients with primary nocturnal enuresis (PNE) were compared with patients with secondary nocturnal enuresis (SNE) for a variety of clinical features, including gender, age when first voiding on their own, age on presentation, infrequent voiding, frequent voiding, urgency, daytime wetting, nocturia, urinary tract infection, constipation, vesicoureteral reflux, attention-deficit/hyperactivity disorder, uroflow results, and ultrasound evidence of a postvoid residual.
Results. The only significant difference between the patients with PNE and those with SNE was in the prevalence of constipation. Constipation was significantly associated with PNE (74.59% vs 57.54%; odds ratio: 2.17; 95% confidence interval: 1.07–4.41). When adjusted for a history of constipation, the age at which a child began to void on his or her own became statistically significant. Patients with SNE started to void on their own at 2.13 years (SD: 0.61), an average of 0.22 years earlier than those with PNE, who started to void on their own at 2.35 years.
Conclusions. PNE and SNE likely share a common pathogenesis. Symptoms of daytime voiding dysfunction are common in patients with PNE and SNE. Daytime voiding habits might influence how the central nervous system responds at night to a full or contracting bladder.
Key Words: primary nocturnal enuresis • secondary nocturnal enuresis • nocturnal enuresis • constipation
Abbreviations: PNE, primary nocturnal enuresis • SNE, secondary nocturnal enuresis • NE, nocturnal enuresis • UTI, urinary tract infection • ADHD, attention-deficit/hyperactivity disorder • VUR, vesicoureteral reflux • OR, odds ratio • CI, confidence interval
Primary nocturnal enuresis (PNE) and secondary nocturnal enuresis (SNE) are generally considered to have a different pathogenesis.1–5 We studied patients who had PNE and SNE and presented at a busy tertiary care pediatric urology voiding dysfunction clinic to determine the differences and similarities in clinical presentation between the 2 groups of patients.
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METHODS |
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All patients who presented with nocturnal enuresis (NE) to the pediatric urology voiding dysfunction clinic at the Health Sciences Center of the University of Oklahoma between October 2003 and April 2004 were recruited into the study. We did not differentiate whether NE was the primary complaint but only whether NE was present.
NE was defined as bedwetting at least once a month. PNE was defined as present when the patient had never achieved a period of nighttime dryness >6 consecutive months. The International Children's Continence Society definition of SNE was used.1 SNE was considered present when the patient had experienced a period of nighttime dryness of at least 6 consecutive months.1
The minimum age for inclusion in the study was 3.5 years. We chose this age because the majority of children achieve daytime and nighttime dryness by this age. Patients were excluded from the study when the parent or guardian did not know whether the child had experienced a period of dryness of at least 6 months, when a structural abnormality of the bladder or urethra was discovered, when a major neurologic problem was present, or when the patient had morbid obesity.
All patients were assessed by 1 of the authors (W.L.M.R.). Patients were instructed to fill out a voiding history form before the assessment. Every patient had a careful history taken and a complete physical examination performed. Each patient was instructed to void into an uroflowmeter (UROCAP; Laborie Medical Technologies, Williston, VT). Immediately after voiding, an ultrasound (LOGIQ 400; General Electric, Chalfont St Giles, United Kingdom) of the bladder was performed to determine whether any residual urine was present. A urinalysis was performed.
The age when the parents considered that their child could void on his or her own was recorded. The age when the child presented for assessment was recorded. For patients with SNE, the age when the wetting developed and the duration of dryness before the onset of NE were recorded. Infrequent voiding was defined as an average of 3 or fewer voids per day. Normal voiding was defined as 4 to 7 voids per day. Frequent voiding was defined as 8 or more voids per day. The presence of nocturia, urgency, or daytime wetting was noted. Daytime wetting was defined as voiding of urine into clothes when the child was awake, whether unintentional or not. For girls, the presence of squatting behavior was noted. Urinary tract infection (UTI) or constipation, if present, was recorded. UTI was defined as a convincing history from the parent of past UTI or evidence of UTI with a urinalysis and urine culture obtained at the clinic visit. Constipation was defined as passage of hard stools, infrequent defecation, or difficulty in passage of stools. Supportive evidence for constipation included palpation of hard stool in the left lower quadrant and visible evidence of appreciable stool on a flat plate of the abdomen. Whether a child had an established diagnosis of attention-deficit/hyperactivity disorder (ADHD) was noted. Whether the uroflow study or postvoid ultrasound was abnormal was recorded. A uroflow study was considered adequate when a minimum of 30 mL of urine was voided. A uroflow was considered abnormal when the curve was other than bell-shaped. Abnormal uroflow curves were divided into tower, interrupted, and obstructive patterns as defined by the International Children's Continence Society.1 A postvoid ultrasound was considered abnormal when the bladder did not empty to completion. Empty to completion was defined as no observable urine in the bladder. When the results of a voiding cystourethrogram (VCUG) were available, the presence of vesicoureteral reflux (VUR) was noted.
A statistical analysis was performed to determine the differences in clinical data between the patients with PNE and SNE. Descriptive statistics were generated. Comparisons between dichotomous variables were assessed using Fisher exact test. Trend analysis and comparisons of categorical variables were performed using 
2. Comparisons between dichotomous and continuous variables were made by evaluation of the t test using the Satterwaite method. The data were modeled using logistic regression using forward, backward, and stepwise selection. Analysis was performed using SAS Version 8.2 (SAS Institute, Cary, NC). The study was approved by the Institutional Review Board of the Faculty of Medicine, University of Oklahoma.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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A total of 192 patients with NE presented during the study. No parent or child refused to participate in the study. Twenty-two patients were excluded from the study. The reasons for exclusion were that a parent or a guardian did not know whether the child had experienced a 6-month period of dryness before presentation (8 patients), structural abnormality of the bladder or urethra (6 patients), major neurologic problem (6 patients), and morbid obesity (2 patients). A total of 123 (72.4%) of the patients had PNE, and the remaining 47 (27.6%) of the patients had SNE. The characteristics of the studied patients are shown in Table 1.
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Data on the gender and the age when the patients presented for clinical assessment and when they started to void on their own are shown in Table 2. Data on frequency of voiding and the presence of nocturia, urgency, squatting behavior, or daytime wetting are shown in Table 3. Twenty-five (35.71%) of the girls with PNE had a history of squatting behavior compared with 11 (37.93%) of the girls with SNE (P = .8231). Data on the presence of UTI, constipation, ADHD, and VUR are shown in Table 4. Data on the presence of an abnormal uroflow or postvoid ultrasound are shown in Table 5.
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The same logistic regression model was chosen by forward, stepwise, and backward selection methods. The age when the child started to void on his or her own (adjusted odds ratio [OR]: 1.763; 95% confidence interval [CI]: 1.02–3.05; P = .0426) and constipation (adjusted odds ratio: 2.50, 95% confidence interval: 1.20–5.20; P = .0143) were significantly associated with PNE.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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PNE and SNE have generally been considered to be separate entities with a different pathogenesis.2–5 For most patients with PNE, the pathogenesis is considered to be related to a problem with arousal, overproduction of urine at night, a small nocturnal bladder capacity, or a combination of these factors.2–4 The common reported causes of SNE include UTI, constipation, urge syndrome/dysfunctional voiding, psychological stress, diabetes, and obstructive sleep apnea.5 A total of 123 (72.4%) of the patients whom we assessed had PNE. This proportion is similar to that observed in other studies.6–8
The only significant difference between the patients whom we report with PNE and those with SNE was in the prevalence of constipation. Constipation was significantly associated with PNE (74.59% vs 57.54%; OR: 2.17; 95% CI: 1.07–4.41; P = .0394). When adjusted for a history of constipation, the age at which a child began to void on his or her own became statistically significant (P = .0426). Patients with SNE started to void on their own at 2.13 years (SD: 0.61), an average of 0.22 years earlier than those with PNE, who started to void on their own at 2.35 years.
There was no significant difference between patients with PNE and SNE when they were compared for frequency of voiding, urgency, daytime wetting, UTI, ADHD, VUR, abnormal uroflow, or postvoid residual urine. There was no significant difference between girls with PNE and SNE when they were compared for squatting behavior.
We were surprised that constipation was not equally prevalent in both groups of children. In our experience, constipation is a common associated problem in children with SNE. We assessed mothers who reported without specific questioning that the SNE in their child was linked directly to the onset of constipation and other mothers who reported that the SNE resolved only when the constipation resolved. Although not equally prevalent, constipation was common in children with SNE and was present in 57.54% of these children. It is possible that constipation might have been underreported in the children whom we report with SNE. Patients with SNE are older and defecate on their own in the toilet rather than under the supervision of a parent. As such, parents of older children with SNE might not be as aware of the frequency and consistency of their child's bowel movements. Most parents cannot report good historical information on these clinical questions, and younger children often cannot help with the history. Another reason that constipation might be underreported is that many children become accustomed to the passage of hard, wide, difficult-to-pass stool and do not complain of any problem to their parents. There are numerous studies that report on the association of constipation and bedwetting.9–11 O'Regan et al9 reported cessation of enuresis in 22 of 32 patients who were treated aggressively for constipation. Loening-Baucke11 studied 234 children with chronic constipation. Daytime and nighttime urinary incontinence was present in 29% and 34% of the children, respectively. Relief of constipation resulted in disappearance of daytime and nighttime incontinence in 89% and 63% of the children, respectively.11 We are not aware of any studies that specifically report on patients with constipation and SNE. The theoretical mechanism whereby constipation might cause enuresis is a direct pressure effect of stool on the bladder. Constipation might be a potential cause of the low nocturnal bladder capacity that is reported as a pathophysiologic factor in bedwetting.2–5
The close similarity in the clinical presentations of the 2 groups suggests that the majority of patients with PNE and SNE might share a common pathogenesis. The common presence of daytime voiding symptoms in patients with both PNE and SNE suggests that daytime voiding habits might influence the attainment of nighttime continence. Urgency is common in preschool children. One of the most common causes of urgency is the tendency of preschool children to ignore the signal of the need to void.12 There are many reasons that preschool children might ignore the signal of the need to void. Ignoring the signal of the need to void during the day might have an influence on how the central nervous system interprets and responds to the signal of a full or contracting bladder at night. During the toilet-training process, children are usually offered considerable attention, encouragement, and rewards to pay attention to the signal of the need to void. Once accomplished, however, most children are not offered the same amount of attention and therefore are possibly less motivated to respond to the signal of the need to void. This often coincides with a developmental stage when children separate more easily from their parents, begin to explore their environment, and discover many new activities that are more compelling than paying attention to their bladder. This behavioral pattern often develops later in the third year of life and is a potential factor in the pathogenesis of urge syndrome, which is a recognized cause of SNE that presents with frequency, urgency, and daytime incontinence, often after a period of normal daytime voiding.5,12 One possible reason to account for our observation that the children who developed SNE started to void at a younger age might be that younger children are able to experience a period of normal nighttime continence before they begin to hold the urine to the last minute and develop urge syndrome as a cause for their SNE. In contrast, children who present with PNE might do so because they are older, have already started to hold the urine to the last minute, have already developed urge syndrome as a consequence, and as such never experienced a period of normal nighttime continence. The third year of life also often coincides with the transition from a child potty chair to an adult toilet. Preschool children who sit on an adult toilet cannot optimally relax their pelvic floor muscles, and this has an influence on bladder and bowel control.13 Failure to relax the pelvic floor muscles likely predisposes children to UTI and constipation, both of which are recognized causes of NE. It is possible that the prevalence of these problems increases during the third year of life. If this were the case, then the PNE observed in older children might reflect the higher prevalence of these problems. We routinely recommend an over-the-toilet seat and a footstool for preschool children to void and defecate to facilitate relaxation of the pelvic floor muscles.14
Identification of symptoms of daytime voiding dysfunction has important clinical implications for the management of NE. In our view, normalization of daytime voiding dysfunction is an important prerequisite to achieve continence at night. In an uncontrolled pilot study, we reported that NE resolved in 22% and improved with at least a 50% reduction in wet nights in an additional 39% of 23 patients who were treated with normalization of daytime bladder and bowel habits and prevention of UTI and without the need of a moisture alarm or medication.14
The most commonly accepted definition of SNE is based on an arbitrary duration of 6 consecutive months of dryness before the onset of wetting.1 Six of the patients whom we assessed with PNE had experienced a period of dryness of at least 3 months. When we compared this group of patients with those with SNE, the results were not significantly different for any of the variables measured (data available on request). Our findings need to be replicated in a larger study before recommending that the definition of SNE be revised to include patients who have experienced dryness for at least 3 consecutive months rather than 6 months.
This study is a preliminary investigation. Consequently, the power of our negative findings is limited. The size of our population had an 80% chance of identifying an absolute difference in incidence of the measured variables of 23% to 25% (depending on the variable).
One major weakness of this study is the low number of patients. Despite the small sample size, 2 statistically significant factors that differentiate SNE from PNE were identified. Another weakness of this study is the selection of patients from a referral rather than from a primary practice. The selection bias from relying on a referral practice to accumulate sufficient numbers of children with enuresis may be unavoidable. NE rates range from 10% to 20% in children 4 to 6 years of age, and an adequately powered study of the general pediatric population would require several thousand subjects.2
Our findings suggest the need for additional study in several areas. The role of constipation to differentiate PNE from SNE needs to be explored further in a study that controls more precisely for the symptoms of constipation and incorporates a better procedure for the self-reporting of these symptoms. Use of a more objective tool, such as the Bristol Stool Form Scale, should be considered in subsequent studies. The incidence of daytime urinary incontinence in the general population needs to be explored with directed questions that explore the rate of minor incontinence. Finally, the efficacy of addressing daytime incontinence as opposed to addressing only nocturnal incontinence in the treatment of PNE and SNE needs to be evaluated further.
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CONCLUSIONS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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PNE and SNE likely share a common pathogenesis. Symptoms of daytime voiding dysfunction are common in patients with PNE and SNE. Daytime voiding habits might influence how the central nervous system responds at night to a full or contracting bladder.
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ACKNOWLEDGMENTS |
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We thank Jill Schanuel, MEd, Research Assistant, Oklahoma University Health Sciences Center, for help with the Institutional Review Board process.
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FOOTNOTES |
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Accepted Aug 19, 2004.
Address correspondence to Wm. Lane M. Robson, MD, Tawam Hospital, Box 15258, Al Ain, United Arab Emirates. E-mail: lanerobson{at}msn.com
No conflict of interest declared.
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PEDIATRICS (ISSN 1098-4275). ©2005 by the American Academy of Pediatrics
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