The role of urodynamics
Multichannel urodynamics act as an extension of the physical examination in the patient with refractory OAB. While urodynamic evaluation is the gold standard for the diagnosis of detrusor overactivity in an OAB patient, the presence or absence of overactivity often does not affect management, as many neurologically intact patients are able to suppress these contractions.
Nevertheless, urodynamics can be a useful adjunct in the evaluation of occult bladder and pelvic floor pathology, such as detrusor sphincter dyssynergia, or in the assessment for potential coexistent stress incontinence. Urodynamics may also be useful in cases of suspected female bladder outlet obstruction from prior sling or urethral surgery.
For males, urodynamics is necessary to evaluate for an obstructing prostate, which would clearly change the treatment plan. From a neurologic standpoint, the filling detrusor pressure and bladder capacity may yield clues regarding a neurologic etiology for OAB. Last, urodynamic testing provides a measure of baseline bladder function, which can be used to objectively measure treatment outcomes.
First-line therapy for idiopathic OAB has typically included anticholinergics and behavioral therapy. Behavioral therapy often involves modification of fluid intake, timed voiding, and pelvic floor exercises in an attempt to block unwanted urinary urgency. Studies have shown a reduction in urge incontinence episodes with these techniques (Clin Obstet Gynecol. 2004;47:70-82).
In the United States, five antimuscarinic agents—oxybutynin, tolterodine, darifenacin, solifenacin, and trospium—are available for the treatment of OAB. These drugs have shown efficacy in the range of 70%-75% for the treatment of urinary urgency and urge incontinence.
Refractory OAB patients who fail oral anticholinergic therapy because of intolerable side effects warrant trial of a different agent. Generally, all anticholinergics have a propensity for M1-mediated side effects, such as dry mouth. However, differences in drug bioavailability, individual patient metabolism, and drug interactions may result in less severe side effects in some patients.
Before considering other options, one should determine that a patient has undergone a satisfactory drug trial (thought to be at least four to six weeks of continuous therapy and best accompanied by behavioral modifications). It is important for clinicians to realize that several drug failures (i.e., lack of efficacy from more than one agent after a satisfactory trial) mandate moving onto refractory therapies or referral to specialized centers to prevent decreased quality of life.
Once a patient is deemed refractory to medications, therapeutic options include off-label use of botulinum toxin injections (BTIs) and neuromodulation before proceeding to the last resort—bladder augmentation. Clearly, the availability of minimally invasive treatment options, such as BTIs and neuromodulation, has resulted in a move away from urinary diversion for the treatment of refractory OAB.
While most of the botulinum toxin studies have focused on use in the neurogenic OAB population, one recent randomized, double-blind, placebo-controlled trial showed beneficial effects in both men and women with refractory OAB using 200 units of intradetrusor injection (J Urol. 2007;177:2231-2236). Specifically, increased mean cystometric bladder capacity and decreased frequency and urge incontinence were seen at 12 weeks. The duration of therapeutic effect is variable, and repeat injections are required.
To maintain treatment benefits, most patients will require repeat injection within an average of six to nine months. The main complication of bladder BTI is urinary retention, and patients must be counseled on this.
A recent study looking at use of BTI in women with refractory OAB found a 60% response (based on a global response instrument); median duration of therapeutic response was longer than 12 months when 200 units were injected. However, post-void residuals were elevated in 43% of BTI recipients (J Urol. 2008;180:217-222). Important questions such as the optimal dose, concentration, and injection location are still being evaluated. Nonetheless, BTIs have allowed larger numbers of refractory patients another treatment option.
The various neuromodulation techniques in use include sacral and tibial nerve stimulation. Available since 1997, sacral neuromodulation (SNM) has the largest body of supporting literature. In a study done in the late 1990s, patients were randomized to neuromodulation or continued conservative management with potential for crossover.
SNM yielded statistically significant improvements in quality of life, pads used, leakage episodes, and severity at six months (Eur Urol. 2000;37:161-171). Neuromodulation via the tibial nerve is entirely an outpatient procedure. Stimulation is applied weekly for a period of 10-12 weeks. Most patients (56%) have a reduction in incontinence episodes. Urinary frequency, QoL, and bladder capacity are improved and the volume at which detrusor activity occurs tends to be delayed (Expert Rev Med Devices. 2007;4:693-698).
Sacral neuromodulation is in current off-label use for bowel dysfunction, and two recent studies have suggested improvement in sexual function in both men and women (J Sex Med. 2008;5:1411-1417). Thus, this form of therapy may provide an option for management of combined pelvic floor disorders.
Overactive bladder in men and women is common, but the exact etiology and epidemiology of the refractory condition is unknown. It is important to rule out anatomic, infectious, neurologic, and malignant causes of symptoms during the initial evaluation.
When conservative measures fail, treatment modalities such as BTIs and neuromodulation are excellent evidence-based options in lieu of bladder augmentation or diversion. Clinicians must always consider refractory options in patients who fail simple, first-line therapy.
Dr. Swartz is a clinical fellow at the Center for Female Pelvic Medicine and Genitourinary Reconstructive Surgery at Cleveland Clinic’s Glickman Urological & Kidney Institute in Cleveland. Dr. Vasavada is the center’s urologic director and he is an associate professor at the Cleveland Clinic Lerner College of Medicine.