Voiding Dysfunction 

Voiding dysfunction is a common problem in children and accounts for as many as 40% of pediatric urology clinic visits. The challenge for the clinician is to differentiate a pathologic pattern of urgency or incontinence due to an underlying urologic abnormality from benign conditions related to incomplete or abnormal toilet training. Normal voiding frequency in children (after attainment of bladder control or age 5 y) is defined as 4-7 voids per day. Voiding symptoms (eg, urgency, frequency, incontinence) reflect alterations in urinary bladder function. The pathogenesis of voiding disorders is best understood and managed when considered as deviations from the normal voiding cycle consisting of bladder filling with urine storage followed by bladder emptying with voiding.

Infants regularly void by detrusor (bladder muscle) contraction as much as hourly, with small voided volumes and incomplete bladder emptying. With increasing age, bladder function matures and bladder capacity increases. Children aged 2-5 years have increased awareness of bladder fullness and develop the ability to volitionally void or 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.

Daytime wetting is considered a problem in developmentally normal children aged 4 years or older who are wet several days each week and in previously continent children who develop daytime wetting.

Persistent daytime urinary incontinence may have an underlying neurologic, anatomic, infectious, or functional basis. This article focuses on daytime voiding disorders in children without neurologic, anatomic, obstructive, or infectious abnormalities of the urinary tract; however, any child with evidence of neurological dysfunction (eg, cutaneous signs, physical examination findings, severely refractory voiding dysfunction, urodynamic evidence of neurogenic bladder) should be further evaluated for occult neurologic lesions. Isolated nocturnal enuresis, which may be considered a form of voiding disorder, is considered elsewhere and is not reviewed here.

The micturition cycle involves 2 discrete processes: (1) bladder filling and storage of urine and (2) 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. The primary neurotransmitter for sympathetic activity is norepinephrine.

Expulsion of urine normally occurs as a result of simultaneous voiding contraction of the detrusor muscle and relaxation of the bladder outlet (urethra, bladder neck, and pelvic floor muscles). This is mediated by the parasympathetic nervous system, in which the primary neurotransmitter is acetylcholine. 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. During the voiding phase, inhibition of the sacral parasympathetic outflow is removed, and detrusor contraction occurs. Somatic impulses traveling along the pudendal nerve act to relax the muscle of the external sphincter. The result is expulsion of urine with minimal outlet resistance.

CNS control over the lower urinary tract coordinates the micturition cycle. Normal development is characterized by increasing awareness of bladder distension and acquisition of the ability to inhibit voiding. Voiding symptoms in the neurologically and anatomically intact child, who has neither a urinary tract infection (UTI) nor local urethral irritation, is a result of functional disturbance of the normal micturition cycle.

Frequency

United States

A study of 583 children aged 5-9 years showed that urinary urgency and pelvic-tightening maneuvers to postpone voiding and prevent leakage were the most common voiding problems.^[1] Urge incontinence was reported in 7% of girls and in 3% of boys.

Daytime wetting has been reported to decrease with age. The prevalence of daytime wetting with a frequency of at least once every 2 weeks was 10% in children aged 5-6 years, 5% in children aged 6-12 years, and 4% in children aged 12-18 years.^[2]

International

A large 2009 study from Australia addressed the frequency of voiding disorders in school-aged children.^[3] This study of 2,856 students reported that 17% of children had experienced daytime incontinence in the previous 6 months. There was not a strong correlation between frequency and number of incontinence episodes. Independent risk factors for daytime incontinence included nocturnal enuresis, female sex, history of UTI, and encopresis.

Mortality/Morbidity

A child with a voiding disorder may have few symptoms or frequent urinary tract problems. Children with functional voiding disorders may have ongoing urge incontinence, urinary dribbling, or recurrent UTIs. These children may experience severe social and emotional problems because of the voiding disorder.

A few children with a functional voiding disorder (ie, nonneurogenic neurogenic bladder [Hinman-Allen syndrome]), have marked dysfunctional voiding and may incur significant renal damage.

Race

No known studies have shown the incidence of voiding disorders related to race.

Sex

Studies on the prevalence of voiding disorders in school children indicate that daytime urinary incontinence is 2-5 times more common in girls.^[3]

Age

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.