Approach Considerations
Noninvasive diagnostic techniques are often used in the diagnostic evaluation of overactive bladder (OAB). Invasive testing is performed for selected indications, including the following:
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Straining or use of the Credé maneuver during voiding
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Weak or decreased urine stream
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Previous febrile urinary tract infection (UTI)
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Continuous dribbling incontinence
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Stress incontinence
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Prior history of vesicoureteral reflux
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Structural abnormalities on physical examination suggestive of an underlying neurologic etiology
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Suspected obstruction
Assessment of bowel function
Bowel habits should be evaluated in all children presenting with overactive bladder symptoms. The Rome III diagnostic criteria are often used to evaluate for constipation, but it is subjective and often relies on parent/guardian description of the child's stools. [19] Other commonly used methods are the Bristol stool form scale [20] and the Leech method to assess the level of stools within the intestine by plain radiography. [21, 22]
Urinalysis
All children who present with OAB symptoms should undergo urinalysis. The primary aim is to rule out underlying UTI or glucosuria.
Ultrasonography
Ultrasonography of the kidneys and bladder is useful in assessing renal size, cortical thickness, hydronephrosis, and duplicated collecting systems and associated anomalies (ectopic ureters and ureteroceles). Ultrasonography of the bladder may be obtained before and after voiding to assess bladder emptying.
In addition, determination of bladder-wall thickness may be useful. [23, 24] A bladder wall cross-section of more than 3-4 mm measured at 50% of expected bladder capacity suggests underlying detrusor overactivity.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) may be useful in some circumstances. MRI of the lumbosacral spine should be considered in children with neurologic abnormalities or a sacral dimple or other presacral abnormality.
Voiding Cystourethrography
Voiding cystourethrography (VCUG) is indicated in children with a history of a febrile UTI or recurrent UTIs, depending on age, to rule out vesicoureteral reflux. It may also be indicated in a child with an abnormal flow pattern to rule out bladder outlet obstruction (eg, from posterior urethral valves, stricture, or syringocele).
A spinning-top dilated proximal urethra revealed by VCUG during the voiding phase suggests detrusor-sphincter dysfunction.
Frequency/Volume Chart or Bladder Diary
A frequency/volume chart or bladder diary is helpful in the evaluation of pediatric OAB symptoms. Ideally, these charts should encompass a 3-day period. This will allow assessment of the child’s functional bladder capacity.
A frequency/volume chart is used to record the volumes voided and the time of each micturition, day and night, for at least 24 hours. A bladder diary is used to record the times of micturitions and voided volumes, incontinence episodes, pad usage, and other such information as fluid intake, the degree of urgency, and the degree of incontinence. A record of the bowel frequency and any fecal soiling is also helpful.
Uroflow Study
A uroflow study is also helpful in the assessment of OAB symptoms and is performed by having the child void into a specialized collection device. The uroflow study can be described in terms of flow rate (mL/sec) and flow pattern. The flow pattern may be continuous, intermittent (interrupted), or staccato (flow does not completely stop but fluctuates because of incomplete relaxation of the sphincter).
Obtain several uroflow studies to achieve consistency. Ninety-nine percent of school children have a bell-shaped flow curve, whereas the remaining 1% have an abnormal flow curve. Such abnormal flow curves include flattened or intermittent flow curves.
For a urinary flow rate to be useful, the voided volume should be at least 50% of the child’s functional bladder capacity. Before the study is initiated, a bladder scan may be helpful in determining the bladder volume.
Uroflow/electromyography study
A uroflow/electromyography (EMG) study involves the placement of perineal electrodes (often patch electrodes) and measurement of EMG activity before, during, and after voiding. Normally, sphincteric activity occurs during bladder filling but silences during voiding. Failure of relaxation or increased sphincteric activity during voiding may suggest a neurologic abnormality or dysfunctional voiding.
Postvoid Residual Volume Study
Postvoid residual volume determination is useful in ruling out dysfunctional voiding as a source of symptoms. In children, except in small infants, the bladder completely empties during each micturition.
An increased postvoid residual volume may be secondary to dysfunctional voiding. If the postvoid residual volume is initially increased, the study should be repeated because the results may not be accurate in an anxious child.
Urodynamic Study
A urodynamic study is an invasive study that should be obtained only in select children with voiding dysfunction. Before this study is performed, the child and parents should be fully aware of what the study entails. If the child is very anxious during the study, the results may be affected, especially during the filling cycle (detrusor overactivity may be noted) or during voiding (incomplete pelvic floor muscle relaxation may be noted).
The urodynamic study has several components. The child is first asked to void just before the study is begun. A sterile urodynamic catheter is then placed via the urethra into the bladder, and the postvoid residual volume is recorded.
Cystometrography
Cystometrography (CMG), also known as filling cystometry, is the component of the urodynamic study that is used to assess the bladder during filling. CMG provides information on the pressure/volume relationship of the bladder during bladder filling.
The bladder should be filled with body-temperature 0.9% sterile saline at a rate of 5-10% of the child’s expected bladder capacity per minute to a maximum rate of 10 mL/min. Contrast material may also be used if fluoroscopic imaging is planned. The bladder capacity is measured during filling cystometry. The cystometric bladder capacity is the bladder volume at the end of the filling CMG, when the child is given permission to void.
The cystometric capacity is the volume voided together with any residual volume. The maximum cystometric capacity in patients with normal sensation is the bladder volume at which the patient feels that he or she can no longer delay voiding (strong desire to void).
The term bladder compliance refers to the relationship between the change in bladder volume and the change in detrusor pressure.
The International Continence Society recommends using the following 2 standard points for compliance calculations [1] :
- The detrusor pressure at the start of bladder filling and the corresponding bladder volume (usually zero)
- The detrusor pressure (and corresponding bladder volume) at cystometric capacity or immediately before the start of any detrusor contraction that causes significant leakage
Detrusor overactivity is a urodynamic observation characterized by involuntary detrusor contractions during the filling phase, which may be spontaneous or provoked (see in the image below).
Phasic detrusor overactivity is defined by a characteristic wave form and may not lead to urinary incontinence. Terminal detrusor overactivity is a single involuntary detrusor contraction occurring at cystometric capacity. It cannot be suppressed and results in incontinence, usually resulting in bladder emptying (voiding). Detrusor overactivity incontinence due to an involuntary detrusor contraction at any point during filling.
Pressure-flow studies
Pressure-flow studies may be obtained during the voiding phase of the urodynamic study. The pressure-flow study involves the plotting of the bladder pressure against the flow rate. This study may be useful when urinary obstruction is suspected.
Videourodynamic studies
Videourodynamic studies are urodynamic studies performed with fluoroscopic assistance. The addition of fluoroscopy allows for the detection of vesicoureteral reflux, a spinning-top urethra (often seen in girls with dysfunctional voiding), and other anatomic abnormalities.
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Urodynamic study demonstrating detrusor overactivity.
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Differential diagnosis of overactive bladder (OAB).
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Uroflow and electromyography (EMG) study demonstrating dysfunctional voiding: staccato flow pattern and failure to relax sphincter during voiding.
