Practice Essentials
The types of voiding dysfunction covered in this article consist of daytime voiding disorders in children who do not have neurologic, anatomic, obstructive, or infectious abnormalities of the urinary tract. The disorders examined result from functional disturbance of the normal micturition cycle. Isolated nocturnal enuresis, which may be considered a form of voiding disorder, is not reviewed here. (See Pathophysiology, Etiology, and Presentation.)
Causes of voiding dysfunction include the following, in isolation or in combination:
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Uninhibited detrusor contractions ( overactive bladder [OAB])
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Dysfunction of the pelvic floor musculature (dysfunctional voiding)
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Decreased force of detrusor contractions (underactive bladder [UAB])
Voiding dysfunction is a common problem in children and accounts for as many as 40% of pediatric urology clinic visits. The challenge for clinicians is to differentiate between a pathologic pattern of urgency or incontinence due to an underlying urologic abnormality and benign conditions related to incomplete or abnormal toilet training. (See Epidemiology, Workup, Treatment, and Medication.)
For patient education information, see the Digestive Disorders Center, as well as Constipation in Children, Bladder Control Problems, and Bladder Control Medications.
Pediatric lower urinary tract dysfunction encompasses a wide spectrum of syndromes. Voiding symptoms (ie, urgency, frequency, incontinence) may be transient, intermittent, or persistent. Transient voiding symptoms are commonly encountered due to urinary tract infection (UTI) or as a result of nonspecific urethritis or periurethral irritation due to vaginitis. Symptoms may also occur without a recognized explanation. No notable findings are apparent upon physical examination of a child with voiding dysfunction; however, a thorough examination should be performed to evaluate for other sources of voiding symptoms.
Urinalysis and quantitative urinary culture should be performed to evaluate for UTI. Evaluation of patients with suspected dysfunctional voiding should be performed by a urologist, and may include voiding cystourethrography (VCUG), urinary tract ultrasonography (US), urodynamic studies, and, in some instances, magnetic resonance imaging (MRI) of the lumbosacral spine to rule out a neurologic etiology.
Behavioral modification is the foundation of treatment for children with functional voiding disorders. Effective biofeedback training is especially helpful for managing dysfunctional voiding. Prophylactic antibacterial therapy should be considered in children with recurrent UTIs and in those with vesicoureteral reflux (VUR). Anticholinergic medications may be helpful in children who do not respond to conservative measures, but they are not long-term solutions. Sacral nerve stimulation is being studied as a means of treating refractory lower urinary tract dysfunction in children.
Pathophysiology
Infants regularly void by detrusor (bladder muscle) contraction as often as hourly, with small voided volumes and incomplete bladder emptying. With increasing age, bladder capacity increases. The coordination between the bladder and sphincter system matures, leading to an improvement in bladder-emptying ability. [1]
Children aged 2-5 years have increased awareness of bladder fullness and develop the ability to void volitionally or to inhibit voiding until it is socially acceptable. During this period, acquisition of cortical control of micturition occurs. Many forms of voiding dysfunction can be thought of as a delay in the acquisition of daytime urinary control, which typically occurs by age 4 years.
Several studies have documented that more than 90% of children achieve full daytime control at age 4 years. [1] This finding suggests that most children are mature enough for independent volitional control of voiding at this age. Daytime wetting is therefore considered a problem in developmentally normal children aged 4 years or older who are wet several days each week, as well as in previously continent children who develop daytime wetting. (See Presentation.)
The micturition cycle involves the following two discrete processes:
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Bladder filling and storage of urine
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Bladder emptying with voiding
These functions are cyclic in nature.
During the filling phase of micturition, regulatory influence of the sympathetic nervous system allows the bladder to expand at low pressure. Urine storage is a coordinated response of the sympathetic-mediated inhibition of detrusor contractile activity. Normal filling requires the absence of involuntary bladder contractions. (The primary neurotransmitter for sympathetic activity is norepinephrine.)
During bladder filling, afferent impulses are transmitted to sensory neurons in the dorsal root ganglia of sacral spinal segments 2-4 and convey information to the brainstem. Nerve impulses from the brainstem during bladder filling inhibit parasympathetic outflow from the sacral spinal micturition center.
Expulsion of urine is mediated by the parasympathetic nervous system (in which the primary neurotransmitter is acetylcholine). During the voiding phase, inhibition of the sacral parasympathetic outflow is removed, and detrusor contraction occurs. At the same time, somatic impulses traveling along the pudendal nerve relax the muscle of the external sphincter. The result is expulsion of urine with minimal outlet resistance.
Central nervous system (CNS) control over the lower urinary tract coordinates the micturition cycle and is initiated in the cerebral cortex. The neural pathway for voiding passes through the pons (Barrington nucleus) and into the spinal cord (Onuf nucleus). Normal development is characterized by increasing awareness of bladder distention and acquisition of the ability to inhibit voiding. Normal voiding frequency in children (after attainment of bladder control or age 5 years) is defined as four to seven voids per day.
Voiding symptoms (ie, urgency, frequency, and incontinence) reflect alterations in urinary bladder function. The pathogenesis of voiding disorders in the neurologically and anatomically intact child who has neither a UTI nor local urethral irritation is best understood and managed when considered as a result of a functional disturbance of the normal voiding cycle (ie, bladder filling with urine storage, followed by bladder emptying with voiding).
Etiology
Causes of voiding dysfunction include the following:
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Uninhibited detrusor contractions (OAB)
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Dysfunction of the pelvic floor musculature (dysfunctional voiding)
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Decreased force of detrusor contractions (UAB)
A study by Oliver et al suggested that children with voiding dysfunction who are underweight, obese, or suffering from a psychiatric disorder or who have recently experienced a stressful event are likely to have a higher lower urinary tract symptom score (as measured through a symptom questionnaire) than other children with voiding dysfunction. [2] In the report, which involved 358 patients (age range, 6-17 y) with nonneurogenic lower urinary tract dysfunction, obesity was found in 28.5%, a recent life stressor in 31.8%, and a comorbid psychiatric disorder in 22.9%. Younger age was also associated with a higher symptom score.
Overactive bladder
OAB (also referred to as detrusor instability, hyperactive bladder syndrome, urge syndrome, and urge incontinence) is the result of overactive detrusor contractions during the filling phase of micturition. Detrusor overactivity is the most common voiding dysfunction in children.
Uninhibited detrusor contractions are thought to result from a lack of inhibitory cerebral control over detrusor contractions during bladder filling. Theories on the cause of OAB have included maturation delay, prolongation of infantile bladder behavior, and abnormality of acquired toilet training habits.
OAB can also occur in children with recurrent UTIs and is a risk factor for UTI. This voiding disorder may contribute to persistence of VUR and to the recurrence of VUR after ureteral reimplantation.
Dysfunctional voiding
Although the etiology is unknown, dysfunctional voiding is thought to reflect a deviation in the normal development of urinary control. As daytime urinary control is achieved, many children go through a transitional phase in which pelvic withholding maneuvers are used to prevent incontinence. Most children then develop a pattern of coordinated voiding that makes it unnecessary to contract the external sphincter to prevent incontinence.
However, some children who have a delay in establishing cerebral control over detrusor contractions continue to use pelvic-tightening maneuvers, and these maneuvers appear to become involuntary over time. Others have suggested that dysfunctional voiding can result from overtraining of the urinary bladder.
A report by Colaco et al indicated that an association exists between a child's temperament and the development of dysfunctional voiding. [3] In a study of 50 children, the investigators found that effortful control tended to be lower in boys with dysfunctional voiding than in those without it. In girls, there was a greater prevalence of urgency among those with dysfunctional voiding.
Underactive bladder
Urinary incontinence in UAB syndrome is usually due to overflow from a large, hypotonic bladder. Patients with persistent voiding symptoms or UTIs should undergo urodynamic evaluation.
Epidemiology
United States statistics
OAB is the most common lower urinary tract dysfunction in children; it appears to have a peak incidence between the ages of 5 and 7 years. [4] In a cross-sectional study, lower urinary tract dysfunction symptoms were detected in 21.8% of school-aged children. The most common urinary symptoms included holding maneuvers (19.1%) and urgency (13.7%). [5] Urge incontinence was reported in 7% of girls and in 3% of boys.
Another study (N = 583; age range, 5-9 y) of children with OAB showed that urinary urgency and pelvic-tightening maneuvers to postpone voiding and prevent leakage were the most common voiding problems. [6]
International statistics
A large (N = 2856) 2009 study from Australia addressed the frequency of voiding disorders in school-aged children. [7] This study reported that 17% of children had experienced daytime incontinence in the previous 6 months. Independent risk factors for daytime incontinence included nocturnal enuresis, female sex, history of UTI, and encopresis.
Age-related demographics
The prevalence of daytime wetting with a frequency of at least once every 2 weeks, as reported in different age groups, is as follows [8] :
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Age 5-6 years - 10%
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Age 6-12 years - 5%
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Age 12-18 years - 4%
A functional voiding disorder in a neurologically and anatomically healthy child is not usually recognized before the acquisition of daytime urinary control.
Many children have a transient period of urinary urgency, occasionally with wetting accidents, when daytime continence is first being achieved. Most of these children develop normal urinary control in a relatively short period; however, some children may have persistence of urinary urgency and wetting.
Other children may have a normal voiding pattern until a UTI or an emotionally traumatic event triggers the onset of voiding symptoms.
Sex-related demographics
Studies on the prevalence of voiding disorders in school children indicate that daytime urinary incontinence is two to five times more common in girls. [7]
Prognosis
The prognosis for complete or partial resolution of a functional voiding disorder is excellent for children with daytime urinary incontinence and detrusor instability.
Children with voiding dysfunction appear to be more likely to have adult OAB or voiding dysfunction. Several studies have reported that childhood incontinence in girls is a risk factor for urge symptoms and severe incontinence as adult women. [9, 10]
The prognosis is good for children with giggle incontinence (involuntary complete bladder evacuation induced by laughter), who tend to outgrow it during adolescence. A resolution rate of 89% was reported in children with this condition who were treated for detrusor instability. [11] The prognosis is also good for children with UAB. The prognosis is guarded, however, for those few children with dysfunctional voiding whose condition does not respond to intervention.
A study of long-term functional and psychosocial outcomes in adolescents and young adults treated during childhood for lower urinary tract dysfunction found that whereas these patients, compared with healthy age-matched control subjects, were more likely to report urinary tract symptoms when older, especially if treatment duration was extensive, their general quality of life and psychosocial well-being later in life were unaffected or only mildly affected. [12]
