Bladder Dysfunction Workup

Laboratory studies indicated in the workup of a patient with neurogenic bladder dysfunction include the following:

• Urinalysis and urine culture with sensitivity to rule out infection
• 24-Hour creatinine clearance
• Residual urine volume

Residual urine volume is usually determined by means of a bladder scan after voiding; it may be measured directly by means of catheterization if bladder scanning is not available. Residual urine volume reflects bladder and outlet activity during the emptying phase of micturition. Up to 100 mL of postvoid residual urine with a voiding frequency greater than every 2 hours is acceptable if the patient is not experiencing frequent urinary tract infections.

Plain radiography of the urinary tract, bladder, and kidneys is indicated to determine the presence of radiopaque calculi (see the image below), in conjunction with ultrasonography. Excretory urography or intravenous pyelography (IVP) may be used for visualization of the collecting system. Isotope studies (eg, technetium-99m dimercaptosuccinic acid [DMSA]) are used for evaluation of renal cortex function.

Ultrasonography is used for routine evaluation of the upper urinary tract. Evaluate for the presence of ureteral obstruction, scarring, masses, and either renal or bladder calculi.

Cystometry helps evaluate the filling and storage phases of detrusor function by measuring changes in intravesical pressure with increases in bladder volume. It assesses the leak point (ie, the pressure at which voiding occurs) and can be used to evaluate the voluntary voiding phase after filling and the efficacy of emptying.

Normal adult bladder capacity is around 400-750 mL, and bladder pressures normally do not exceed 15 cm H₂ O during the filling phase. Bladder volumes can be determined and recorded during first sensation of filling, voiding urgency, and maximal filling.

Abnormal findings include decreased bladder compliance with intravesical pressures exceeding 15 cm H₂ O and a steep rising curve in the cystometrogram, possibly due to bladder inflammation, bladder fibrosis, or detrusor hypertrophy.

Involuntary detrusor contraction (ie, a phasic increase in intravesical pressure during the filling phase) reflects the presence of detrusor hyperreflexia in patients with suprapontine lesions (eg, from a cerebrovascular accident [CVA] or Parkinson disease). This phenomenon also is seen in patients with suprasacral spinal cord disease (eg, spinal cord injury [SCI], multiple sclerosis [MS], or spina bifida).

A noncompliant bladder with reduced capacity demonstrates a steep curve associated with neurogenic lesions, inflammation, or severe outlet obstruction.

A leak point in excess of 40 cm H₂ O may result in hydronephrosis in children with myelomeningocele.

An absence of contractions during attempts to void, as is noted with areflexic bladders, may be seen in patients with sacral lesions. Peripheral neuropathy can develop from conditions such as diabetes mellitus.

Electromyography (EMG) is used to measure electrical potentials generated by depolarization of the detrusor muscle and the urethral sphincter.

Anticipated normal findings include an incremental increase in EMG activity in the external sphincter during the filling phase secondary to increased recruitment of motor units. Before voiding, diminished EMG activity in the external sphincter is expected. Relaxation of the external sphincter is followed by bladder contraction.

Abnormal EMG patterns include absence of recruitment and low levels of EMG activity, as in patients with complete SCI. An inappropriate increase in EMG activity of the sphincter may be observed, leading to detrusor contraction against a closed sphincter or detrusor-sphincter dyssynergia. Potential findings include confirmation of detrusor-sphincter contraction dyssynergia, increased duration of bladder contractions, and uninhibited bladder contractions.

Cystoscopy is indicated in patients with recurrent urinary tract infections, especially those with bladder stones. It is also indicated for investigating the possibility of tumor or assessing trauma. Finally, it is useful for evaluation of the bladder outlet and urethra.

The evidence for or against the use of urodynamics rather than other methods for assessing bladder function in poststroke patients with urinary incontinence and bladder dysfunction is insufficient; however, urodynamics may be useful as an adjunctive diagnostic tool.^[12]

Evaluation of complex lower urinary tract pathology is performed by using videourodynamics. This technique involves EMG studies during 3 phases, in conjunction with periodic screening of synchronous cystourethrographic studies of the bladder and outlet. Videourodynamics is particularly useful for the detection of sites of bladder outlet obstruction and detrusor-sphincter dyssynergia.