Recommendations for research
2.4.2 Diagnosing detrusor overactivity and impaired bladder compliance
Normally, the bladder stores urine at a low pressure and does not contract involuntarily. Once capac-ity is reached or voluntary voiding is desired, intravesical pressure increases (voluntary detrusor contraction). This is preceded by a relaxation of the external sphincter.
Detrusor overactivity is a urodynamic observation characterized by IDCs during the filling phase, which may be spontaneous or provoked. Detrusor overactivity may be further characterized as neurogenic DO, which means that it is associated with a relevant neurological condition (e.g. spinal cord injury or multiple sclerosis) or idiopathic DO, which mean that there is no defined cause (it is non-neurogenic) (4).
Characteristically, DO is associated with symptoms such as urgency, frequency, and urgency incon-tinence. However, this is not a diagnosis but a urodynamic observation, the cause of which is some-times clear (e.g. a neurological disease such as multiple sclerosis) but is often obscure. For example, it has been argued that DO may be caused by urethral obstruction, and this is discussed further below.
In other cases, there is no obvious cause, and the DO is called idiopathic. Sometimes it may even be a normal variant.
As stated above, DO is often (but not always) associated with urgency and urgency incontinence. But not all patients with urgency or urgency incontinence demonstrate DO on UDS studies. In the first study correlating the latest ICS OAB terminology with UDS findings, Hashim et al. (220) showed that the bladder is a better and more reliable witness in men than in women, with a greater correla-tion between OAB symptoms and urodynamic DO. This was even more apparent in OAB wet than in OAB dry patients. Men with urgency incontinence had DO in 84.2% of cases vs. 59.8% of those without. Those with urgency had DO in 78.6% of cases vs. 46.5% of those without. The symptom of frequency did not increase the likelihood of finding DO.
The presence of DO during UDS must be interpreted in the context of the patient’s symptoms and condition. Ideally, a patient’s symptoms should be reproduced during UDS, so we would expect DO to be accompanied by urgency or urgency incontinence, although it can occur and be significant without being symptomatic, particularly in neurogenic DO. However, DO can also be test induced or clinically insignificant, and has been reported in 14%–18% of healthy asymptomatic volunteers undergoing UDS (221–223). Several studies have investigated UDS findings in men prior to prostate cancer surgery and the incidence was 17%–60%, with some studies reporting DO of significant pres-sure magnitude (224–229).
The specific characteristics of DO can also be noted. Detrusor overactivity can manifest as a single event or as multiple IDCs. It can be phasic (continuous), sporadic, or terminal (occurring at the end of filling, near capacity). The ICS specifically defined three patterns of DO (4):
1. Phasic DO has the characteristic wave form and may or may not lead to UI.
2. Terminal DO is defined as a single IDC occurring at cystometric capacity that cannot be suppressed and results in inconti-nence, usually resulting in bladder emptying (voiding).
3. Detrusor overactivity incontinence is inconti-nence due to involuntary detrusor contraction.
Other characteristics of DO have also been reported, such as maximum Pdet during IDC and volume at first IDC.
Subclassifying DO in this way may be valuable in certain circumstances. For example, Kageyama et al. (230) showed that OAB symptoms associated with obstruction had a higher likelihood of resolv-ing with intervention (e.g. TURP) when DO occurred as a sresolv-ingle terminal IDC rather than continu-ous or sporadic IDCs.
More recently, Shahab et al. (231) investigated the relationship of DO profiles (including the ampli-tude of DO or the maximum DO pressure, the time to reach maximum DO pressure, the ratio of amplitude to time, the total time of DO, the bladder volume at the first DO, and the Pdet at the first DO) and DO patterns (terminal vs. phasic), and their correlation with symptoms. The authors retro-spectively reviewed the UDS of 231 men with BPE who underwent TURP. Terminal DO was found in 127 patients (55.0%), while phasic DO was found in 104 patients (45.0%). Incontinence absence at DO was found in 104 (45%), while incontinence presence at DO was found in 127 (55%). Multiple DO was found in 83 patients (35.9%), while single DO was found in 148 patients (64.1%). No correlation was found between DO profiles and the severity of symptoms related to OAB. However, the scores of the urgency symptoms were significantly higher in terminal DO than in phasic DO, while the nocturia symptom scores were found to be significantly higher in single DO in comparison to those found in multiple DO. Terminal DO has higher amplitude and duration of DO contraction. The authors postulated that because of this, terminal DO accounts for more severe urgency symptoms, due to activation of sensory afferent nerves by increased Pdet and duration of contraction. They did not comment on outcomes of TURP.
Bladder compliance describes the relationship between change in bladder volume and change in Pdet. The normal bladder is highly compliant: i.e. during artificial filling, the Pdet rises by at most 10 or 15 cm H2O, while the bladder is filled to a volume of about 500 mL. If natural filling by diuresis is used, the pressure rise is even smaller. A steeper pressure rise (in the absence of DO) implies abnor-mally low compliance–a “stiff” bladder wall.
Compliance is calculated by dividing the volume change by the change in Pdet during that change in bladder volume. It is expressed in mL/cm H2O. A variety of means of calculating bladder compliance have been described. The ICS (4) recommends that two standard points should be used for compli-ance in most circumstcompli-ances. Both points are measured excluding any detrusor contraction:
1. The Pdet at the start of bladder filling and the corresponding bladder volume (usually zero)
2. The Pdet (and corresponding bladder volume) at cystometric capacity or immediately before the start of any detrusor contraction
that causes significant leakage (and therefore causes the bladder volume to decrease, affect-ing compliance calculation)
Low compliance appears to always reflect pathology, and is well known to be associated with upper tract damage secondary to pressure transmission from the bladder to the kidneys, by reflux or ureteral obstruction. An association between low compliance and urethral obstruction has been reported but is uncertain. While it is known that some patients with obstruction develop impaired compliance and/or bladder decompensation, these events cannot be predicted early on before structural changes occur. Therefore, a critical level of obstruction has not been defined; there are no evidence-based studies to suggest when surgical relief is indicated to prevent bladder decompensation. Leng and McGuire (232) did show that relieving BPO with TURP led to improved bladder compliance in a small cohort of men with BOO and significantly impaired compliance.
What then can be said about the utility of diagnosing DO and impaired compliance in the male with LUTS? This is probably best summarized in the recently published AUA/SUFU UDS guidelines, which state: “Clinicians may perform multichannel filling cystometry when it is important to deter-mine whether DO or other abnormalities of bladder filling/urine storage are present in patients with LUTS, particularly when invasive, potentially morbid, or irreversible treatments are considered.”
This guideline is based on expert opinion, as the panel found no relevant studies that met the inclu-sion criteria regarding the usefulness of cystometry for guiding clinical management in patients with LUTS (174). Even though cystometry is the diagnostic standard for LUTS and some conditions associated with LUTS, it often fails to explain symptoms (233), and the reproducibility of finding DO from one study to another in the same patient can vary whether the studies are performed consecu-tively or on different days (234). The panel also found considerable variation in studies attempting to determine the usefulness of UDS to help predict prognosis after treatment of LUTS. However, despite that fact that the presence or absence of DO has not been shown to consistently predict specific treatment outcomes, the panel believes that there are instances in which a particular treat-ment for LUTS might be chosen or avoided based on the presence of DO and (more importantly) impaired compliance, particularly when invasive or irreversible treatment is planned, as it could aid in patient counseling. While there are no data to support or refute this recommendation, the AUA/
SUFU UDS Guidelines Panel felt that for many clinicians, the presence of DO or impaired compli-ance remains an important piece of information in treatment decisions.