Urodynamic Assessment of Overactive Bladder - Neurogenic and Nonneurogenic

Introduction
Urodynamic studies (UDS)  generate information about bladder function that, currently, no other testing can provide. Though clearly not necessary to evaluate all lower urinary tract symptoms (LUTS), UDS can be useful when confronted with situations in which the normal noninvasive parameters used to assess LUTS, such as questionnaires, flow rates, and postvoid residual testing, are not helpful.

There are a few keys to developing a successful urodynamic laboratory and to conducting studies that can be readily interpreted and utilized for clinical planning. Perhaps the foremost among these are the ability to re-create the LUTS in question during the UDS and training capable technicians who understand the equipment and the patients so that they are able to accomplish this task. Having the clinician present or readily available during the study is essential to generating interpretable data. A poorly conducted UDS test will tell you nothing about the symptom or problem in question, may only serve to further muddy the clinical picture, and may dissuade the patient from further care. On the other hand, a properly conducted test will give insight into the pathophysiology underlying the clinical condition, may provide some type of assessment of risk to the patient of leaving the condition untreated, and will clearly help guide management.

This section discusses the role of UDS in assessing patients with overactive bladder (OAB), both neurogenic and idiopathic, and the common findings seen in each of these conditions are reviewed.

Who Requires Urodynamics?
The issue of the optimal evaluation for OAB remains contentious. Although few would argue that patients with known neurological conditions and bladder dysfunction merit a thorough urodynamic evaluation to establish risk assessment and determine appropriate therapy, the same cannot be universally said of patients with OAB symptoms and no known neurological condition.

It seems clear that, in most patients with classic urinary symptoms of urinary urgency, frequency with or without urge urinary incontinence, a thorough history, physical examination, and urinalysis should be carried out prior to instituting any type of medical therapy for OAB. It is further clear that validated urinary questionnaires and voiding diaries, at least 48–72 h in duration, can provide additional information about severity of frequency and incontinence, functional bladder capacity, overall urine production, and degree of nocturia, which may be difficult to ascertain otherwise ⁽¹⁾. Each of these assessments can provide insight into the proper treatment. Measuring postvoid residual in women without prolapse, previous incontinence, or prolapse surgery;  no history of recurrent bladder infections; and without voiding symptomatology (straining, hesitancy, staccato voiding)  is generally considered unnecessary in most patients with OAB symptoms because overall the prevalence of elevated residuals is low ⁽²⁾.

The controversy surrounding the use of urodynamic testing in OAB involves three basic principles. The first principle is that many women with no specific bladder complaints will be found to have “abnormal” findings on urodynamic testing. Indeed, idiopathic detrusor overactivity may be found in up to 69% of asymptomatic patients undergoing ambulatory UDS ⁽³⁾. Advocates of ambulatory urodynamic studies note that these outpatient studies may establish a diagnosis in as many as 56% of patients in whom conventional studies were unable to do so ⁽⁴⁾. Still, although some contend that urodynamically diagnosed bladder dysfunction may merit treatment in women with LUTS who do not specifically complain of OAB-type symptoms ⁽⁵⁾, more often than not it is unclear that findings noted only during urodynamics require treatment.

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Indeed, the inability of UDS to correlate closely with LUTS is the second principle surrounding the controversy of UD usefulness. Because conventional in-office studies take place over a short window of time, it is not uncommon for them to inadequately demonstrate the cause of LUTS, particularly in the case of urgency and urge incontinence. In general, about 18–23% of patient with OAB-type symptoms and incontinence may have normal urodynamic findings ^(6,7). Furthermore, a meta-analysis of studies investigating the ability of UD testing to diagnose bladder dysfunction accurately noted a sensitivity of only 45–72%  for OAB/urge incontinence, with somewhat higher figures noted for stress incontinence ⁽⁸⁾. We found that utilizing the Urogenital Distress Inventory Questionnaire allowed us to improve the sensitivity of diagnosing detrusor overactivity in patients with either urinary frequency or urge incontinence to 75–83%, although the questionnaire was inadequate at predicting voiding disturbances ⁽⁹⁾.

Last, it is unclear, even if one can accurately diagnose OAB in patients with LUTS highly suggestive of this condition, that urodynamic findings will allow us to predict optimal treatment based on UD findings. For example, it has not been conclusively demonstrated that particular anticholinergic medications are superior based on indices of bladder function obtained during cystometry (such as capacity, threshold volume for detrusor contractions, or amplitude of detrusor contractions) or that overall treatment response to any anticholinergic medication is predictable based on UD findings.

A crossover study of tolterodine and oxybutynin noted no difference in treatment efficacy based on severity of OAB as defined urodynamically, although there was the suggestion that patients with high-amplitude contractions did not fare as well on either medication ⁽¹⁰⁾. Other studies have noted no influence of urodynamic parameters on efficacy of medical treatment, local estrogen, or bladder training ^(11,12).

Therefore, the decision to perform urodynamics remains controversial and, in many cases, experientially based. Among the most commonly accepted reasons to perform urodynamic testing in nonneurogenic female patients with OAB symptoms include failure to respond adequately to pharmacological management, the presence of voiding symptoms, history of incontinence or prolapse surgery, recurrent urinary tract infections, and concurrent pelvic prolapse. Male patients, many of who are commonly treated with α-blockers or 5α-reductase inhibitors, may require urodynamics if medical management does not improve symptoms, particularly if surgery for presumed outlet obstruction is under consideration.

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Gary E. Lemack, MD
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