A significant challenge when performing UDS in patients with NGB is the reproduction of their clinical symptoms during the study. For many NGB patients there is an inherent lack of symptomatology due to impaired bladder sensation. In addition, the degree of symptomatology does not necessarily correlate with findings on UDS, even in the neurologically intact patient. For neurogenic patients, not only this is true, but the degree of symptomatology also does not necessarily correlate with the magnitude of their disease affecting the urinary tract. Many patients may be at risk for upper tract disease but are entirely asymptomatic. Patients also may not be fully aware of symptoms and therefore cannot describe whether their leakage is associated with urinary urgency or stress maneuvers such as transfers. They may have altered bladder sensation or no bladder sensation at all. All of these factors make it more challenging to reproduce symptoms in patients with NGB.

According to Good Urodynamic Practice Guidelines, repeat UDS studies are recommended if “the initial test suggests an abnormality, leaves cause of troublesome lower urinary tract symptoms unresolved, or if there are technical problems preventing proper analysis” [3]. If these guidelines are to be followed, all NGB patients would require repeated studies.

Bellucci et al. [4] addressed this in a prospective study of 226 NGB patients who underwent same session repeat UDS, looking at repeatability based on 95 % limits of agreement. The only measure found to have good repeatability was detrusor overactivity. The other measures including maximum cystometric capacity, compliance, maximum detrusor storage pressure, detrusor leak point pressure, and voiding parameters (in the 88 patients who were able to void spontaneously) were not consistent between studies. The authors suggest that the clinical decision-making not be based on one UDS filling, but should base it on multiple cycles and concentrate on the results that cause concern. Another study by Ockrim et al. [5] confirmed that detrusor overactivity is repeatable in patients with NGB, but not necessarily repeatable for men with LUTS. This study did not comment on other urodynamic parameters in spinal cord injury (SCI) patients.

Ambulatory UDS has been used to mimic a more physiologic filling of the bladder. Virseda et al. [6] looked at the test-retest repeatability of two ambulatory UDS 24 h apart in 66 patients with SCI. They found no significant differences between the two studies for bladder capacity, maximum detrusor pressure during a detrusor contraction, and post-void residual. However, they found that filling pressure was not reproducible, which is concerning as the filling pressure is directly related to upper tract damage.

This reinforces the importance of looking at the entire clinical picture in the neurogenic patient. It is also often helpful to obtain history from family members or caretakers as they can give insight into bladder behavior that the patient might be unaware of.

As previously stated, there are no current guidelines on how often UDS should be repeated in the NGB population. The real question would be to ask how often do UDS change a patient’s bladder management. Nossier et al. [7] performed a retrospective review of 80 SCI patients who underwent UDS once a year for at least 5 years to determine how often treatment is modified based on UDS results. They defined treatment success as detrusor pressure <40 cm of water during filling and <90 cm of water during voiding as well as absence of AD, <3 urinary tract infections (UTIs) per year, one continence pad per day, and no hydronephrosis or scarring on renal ultrasound. With a mean follow-up of 67.3 months, no patient had signs of renal damage and 77 of 80 patients ultimately required treatment modification based on urodynamic findings during the study period. Of patients who were symptomatic at time of UDS, all of them had abnormalities on UDS. More importantly, 68 % of clinical failures would have been undetected based on symptoms alone.

As UDS are time consuming and expensive, attempts at using other clinical tools to assess a patient’s need for UDS have been explored. Pannek et al. [8] looked at the use of detrusor wall thickness at various bladder volumes and its correlation to favorable urodynamic results and found that it was sensitive to determine the patients with no risk factors for renal damage; however, clinical parameters such as detrusor overactivity and incontinence could not be evaluated and may require further evaluation with UDS regardless of risk of renal damage.

Many NGB patients also have neurogenic bowel and most have a home bowel regimen. If patients are not on a bowel regimen, it may necessitate bowel evacuation prior to the study to allow accurate rectal catheter pressure readings [9]. If patients are already on a bowel program, rectal suppositories or enemas should be administered with enough time prior to the study to allow the medication to take effect and avoid bowel movements during the procedure.

UDS can be performed in the supine, sitting, standing positions, or even while ambulating [10]. Many patients with NGB have significant limitations in their mobility that do not allow them to sit on or stand at a commode like a typical patient. Keeping in mind that many patients do not void into a toilet, it is perfectly acceptable for neurogenic patients to be in the supine position for urodynamic testing. It is important that they are comfortable and that excess pressure on any limbs is avoided as this may lead to skin breakdown or even autonomic dysreflexia (AD). If performing a study with fluoroscopy (FUDS), it is ideal for patients to be placed in an oblique position to allow for better visualization of the bladder neck. In this case, voided urine may be collected in a wide-bore drainpipe with length to reach the flowmeter. When possible, patients who volitionally void may be able to sit on a commode more easily which would allow for measurement of pressure-flow. Patients might require study repetition in multiple positions, especially if expected results are not achieved in the supine position.

The first case of autonomic dysreflexia (AD) was first described as hot flushes in a C5 SCI patient by Hilton in 1960 [11]. Subsequent reports included patients with a variety of symptoms including hot flushes, sweating with bradycardia, and an increase in blood pressure (BP) associated with a distended bladder [12, 13]. In 1947 Guttman and Whitteridge then more fully described the autonomic response after distension of the abdominal viscera leading to effects on cardiovascular activity in SCI patients [14].

AD occurs in approximately 60 % of cervical and 20 % of thoracic SCI patients. The most common etiology is bladder or rectal distension, either spontaneous or by instrumentation. Other etiologies include plugged catheters, urinary tract stones, long bone fracture, decubitus ulcers, or even electroejaculation.

Classic signs of AD include an increase in BP with bradycardia, although true bradycardia is only seen in approximately 10 % of patients. In fact, tachycardia or no significant change in heart rate is more common in patients with AD. Other signs may include cardiac arrhythmias, changes in skin temperatures (vasodilation above the lesion, vasoconstriction below the lesion), or changes in mentation.

Common symptoms include sweating above the lesion, pounding headache, hot flushes, piloerection, nasal congestion, dyspnea, and anxiety. Although we think of patients presenting with these classic symptoms, some patients may be entirely asymptomatic. A study by Linsenmeyer et al. [15] demonstrated that 35 of 45 patients with SCI above T6 were asymptomatic with a significant elevation of BP. This stresses the importance of monitoring BP during procedures as AD may be missed in an asymptomatic patient with possible devastating outcomes including seizures, stroke, or even death. During a UDS study it is generally recommended to obtain a baseline BP and cycle the BP during regular intervals throughout the study (Fig. 9.1).