# Overactive Bladder and Voiding Dysfunction

## Overactive Bladder (OAB)

### Definition

Overactive bladder is a symptom syndrome characterized by urgency, defined as a sudden compelling desire to urinate that is difficult to defer, with or without urgency incontinence, usually accompanied by frequency (8 or more voids per day) and nocturia (one or more voids per night). The diagnosis is clinical and based entirely on symptoms; no specific test is required. Urinary tract infection, bladder pathology, and other causes of urgency must be excluded.

### Epidemiology

The prevalence of OAB is 12 to 17% of adults and increases with age. Women and men are affected roughly equally, though women more commonly experience urgency incontinence. Approximately one-third of OAB patients have urgency incontinence ("OAB wet"), while two-thirds have urgency without incontinence ("OAB dry"). The condition is significantly underdiagnosed and undertreated.

### Pathophysiology

Detrusor overactivity, defined as involuntary detrusor contractions during bladder filling, is the urodynamic correlate, though OAB remains a symptom-based diagnosis rather than a urodynamic one. Neurogenic causes include central nervous system lesions from stroke, multiple sclerosis, Parkinson disease, or spinal cord injury that remove cortical inhibition of the micturition reflex. Myogenic causes involve changes in detrusor smooth muscle properties from denervation, ischemia, or aging. Urothelial and afferent dysfunction from abnormal sensory signaling is another mechanism. In most cases, the cause is idiopathic with no identifiable neurologic or anatomic explanation.

### Differential Diagnosis

The differential includes urinary tract infection, bladder cancer or carcinoma in situ, bladder stones, interstitial cystitis/bladder pain syndrome, atrophic vaginitis or genitourinary syndrome of menopause, polyuria from diabetes mellitus or diabetes insipidus, medications (diuretics, cholinesterase inhibitors), excessive fluid or caffeine intake, and neurologic conditions such as multiple sclerosis, stroke, and Parkinson disease.

### Evaluation

Symptom assessment uses validated questionnaires such as the OAB-q, UDI-6, or ICIQ. A voiding diary of at least 3 days documents frequency, volumes, fluid intake, and incontinence episodes. Urinalysis rules out infection and hematuria. Post-void residual measurement rules out retention, which is especially important before starting anticholinergic therapy. Urodynamics are not required for initial diagnosis and are reserved for complex cases, failed treatment, or preoperative evaluation. Cystoscopy is indicated when there is hematuria, recurrent UTI, suspected bladder pathology, or refractory symptoms.

<image>Diagnostic evaluation flowchart for overactive bladder: starting with symptom assessment and voiding diary, then urinalysis and PVR measurement, with decision points for when to proceed to urodynamics (failed treatment, diagnostic uncertainty) or cystoscopy (hematuria, recurrent UTI, refractory symptoms), and when empiric treatment can begin</image>

## OAB Treatment

### First-Line: Behavioral and Lifestyle Therapies

Bladder training uses scheduled voiding with gradual interval increases, starting at the current voiding interval and increasing by 15 to 30 minutes per week, with a goal of 3 to 4 hour voiding intervals. Urge suppression is an integral technique: when urgency occurs, the patient stops, contracts the pelvic floor, waits for the urge to pass, and then walks to the bathroom. Pelvic floor muscle training works because pelvic floor contractions inhibit detrusor contractions via a spinal reflex, and supervised therapy by a pelvic floor physical therapist produces the best results. Dietary modifications include reducing caffeine (which has significant evidence for improvement), moderating alcohol intake, avoiding bladder irritants such as artificial sweeteners, spicy foods, carbonated beverages, and citrus, and maintaining appropriate fluid management of approximately 6 to 8 cups per day. Weight loss reduces all urinary symptoms including OAB. Timed voiding and prompted voiding are appropriate strategies for cognitively impaired patients.

### Second-Line: Pharmacotherapy

#### Antimuscarinic (Anticholinergic) Agents

Antimuscarinics block M2 and M3 muscarinic receptors on the detrusor muscle, reducing involuntary contractions. Options include oxybutynin immediate release at 5 mg two to three times daily (highest side effects but least expensive), oxybutynin extended release at 5 to 30 mg daily (fewer side effects), oxybutynin transdermal patch at 3.9 mg/day applied twice weekly (fewer systemic side effects), oxybutynin topical gel at 10% daily, tolterodine extended release at 2 to 4 mg daily, solifenacin at 5 to 10 mg daily, darifenacin at 7.5 to 15 mg daily (M3 selective with theoretically less cognitive effect), fesoterodine at 4 to 8 mg daily, and trospium at 20 mg twice daily (which does not cross the blood-brain barrier and is therefore preferred in elderly patients). Side effects include dry mouth (the most common), constipation, blurred vision, cognitive impairment, drowsiness, tachycardia, and urinary retention. Anticholinergics are listed as potentially inappropriate in older adults by the AGS Beers criteria because the cumulative anticholinergic burden increases dementia risk. Beta-3 agonists should be considered as first-line pharmacotherapy in patients aged 65 and older.

#### Beta-3 Adrenergic Agonists

Mirabegron at 25 to 50 mg daily and vibegron at 75 mg daily activate beta-3 receptors on the detrusor muscle, promoting relaxation during filling. Their main advantage is the absence of anticholinergic side effects and a better cognitive safety profile. Side effects include hypertension (blood pressure should be monitored), nasopharyngitis, UTI, and headache. They are contraindicated in uncontrolled hypertension. They can be combined with antimuscarinic agents for refractory cases, as demonstrated in the SYNERGY trial evaluating solifenacin plus mirabegron.

#### Vaginal Estrogen

Topical vaginal estrogen in the form of cream, tablet, or ring improves urogenital atrophy from genitourinary syndrome of menopause and reduces urgency, frequency, and urgency incontinence. It is safe for long-term use with minimal systemic absorption and serves as an adjunct to other OAB therapies.

### Third-Line: Neuromodulation and OnabotulinumtoxinA

#### OnabotulinumtoxinA (Botox) Injection

One hundred units are injected into the detrusor via cystoscopy at 20 injection sites, sparing the trigone. The mechanism involves blocking acetylcholine release at the neuromuscular junction and modulating afferent signaling. Approximately 60 to 70% of patients achieve at least a 50% reduction in urgency incontinence episodes. The average duration of effect is 6 to 9 months, and repeat injections are needed. The risk of urinary retention requiring clean intermittent catheterization is 5 to 10%, and patients must be willing and able to self-catheterize. It is FDA-approved for OAB refractory to anticholinergics.

#### Sacral Neuromodulation (InterStim)

An implanted neurostimulator delivers electrical impulses to the S3 sacral nerve. The mechanism involves modulating pelvic nerve reflexes and restoring balance between inhibitory and excitatory inputs. A staged approach starts with test stimulation via a staged lead for 1 to 2 weeks; if at least 50% symptom improvement occurs, a permanent generator is implanted. Efficacy shows 70 to 80% improvement with durable long-term benefit. It is also approved for non-obstructive urinary retention and fecal incontinence. MRI-compatible devices are now available. Risks include lead migration, infection, need for revision or replacement, and pain at the implant site.

#### Posterior Tibial Nerve Stimulation (PTNS)

A percutaneous needle electrode is placed near the posterior tibial nerve at the medial ankle. Weekly 30-minute office sessions are conducted for 12 weeks, followed by monthly maintenance. The mechanism involves retrograde stimulation of the sacral nerve plexus via the tibial nerve. Efficacy is similar to antimuscarinic medications at 60 to 70% improvement. It is minimally invasive with no implant but requires ongoing maintenance sessions. Implantable tibial nerve stimulators are emerging.

<image>Illustration comparing the three third-line OAB treatments: Botox injection showing cystoscopic view of detrusor injection sites, sacral neuromodulation with the InterStim device implanted and lead at S3 foramen, and PTNS with percutaneous needle placement at the medial ankle near the posterior tibial nerve</image>

## Voiding Dysfunction

### Urinary Retention

Acute retention presents as a sudden inability to void with a painful, distended bladder requiring catheterization. Chronic retention involves an elevated post-void residual above 200 to 300 mL with or without overflow incontinence. Causes in women include postoperative retention (the most common, following anti-incontinence surgery, prolapse repair, or hysterectomy), medications (anticholinergics, opioids, alpha-agonists, anesthesia), neurogenic causes (multiple sclerosis, spinal cord injury, diabetes, cauda equina syndrome), pelvic mass or prolapse causing outlet obstruction, detrusor underactivity from aging, diabetes, or neurologic disease, and dysfunctional voiding from pelvic floor dyssynergia.

### Management of Urinary Retention

Acute retention is managed with Foley catheter drainage, with the volume measured and a trial of voiding attempted after the underlying cause is addressed. For chronic retention, clean intermittent catheterization performed 4 to 6 times daily is the gold standard. Alpha-blockers such as tamsulosin may help in bladder outlet obstruction. Sacral neuromodulation is FDA-approved for non-obstructive retention. Pelvic floor physical therapy is the primary treatment for dysfunctional voiding. An indwelling catheter or suprapubic catheter is reserved as a last resort.

### Dysfunctional Voiding

Dysfunctional voiding is the inability to relax the pelvic floor or external urethral sphincter during voiding. It leads to incomplete emptying, elevated post-void residual, and recurrent UTI. Diagnosis is made by urodynamics showing increased EMG activity during voiding. Treatment involves pelvic floor physical therapy with biofeedback, behavioral training, and timed voiding.

## Clinical Pearls

OAB is a symptom-based diagnosis. Urodynamics are not required to initiate treatment in uncomplicated cases.

Behavioral therapy combining bladder training and pelvic floor muscle training should always be offered first. Pharmacotherapy is adjunctive, not primary.

In elderly patients, avoid anticholinergics as first-line treatment. Use beta-3 agonists (mirabegron or vibegron) due to the cognitive risk associated with anticholinergics.

Caffeine reduction alone can significantly reduce urgency and frequency and should always be addressed in counseling.

Patients must be counseled about the 5 to 10% risk of urinary retention requiring self-catheterization before Botox injection.

Sacral neuromodulation is effective for both refractory OAB and non-obstructive urinary retention and should be considered when other treatments fail.

Always check a post-void residual before starting anticholinergic medication to rule out pre-existing retention.

Vaginal estrogen is an underutilized adjunct for OAB in postmenopausal women, addressing the atrophic component of urgency and frequency.

## References

- AUA/SUFU Guideline: Diagnosis and Treatment of Overactive Bladder (Non-Neurogenic) in Adults (2019, amended 2023)
- ACOG Practice Bulletin No. 155: Urinary Incontinence in Women (2015)
- Gormley EA et al. Diagnosis and treatment of overactive bladder (non-neurogenic) in adults: AUA/SUFU guideline amendment. J Urol. 2015;193:1572-1580
- Nitti VW et al. OnabotulinumtoxinA for the treatment of patients with overactive bladder and urinary incontinence. J Urol. 2013;189:2186-2193
- Herschorn S et al. (SYNERGY study). Efficacy and safety of combinations of mirabegron and solifenacin. Eur Urol. 2017;72:471-481
- Chapple CR et al. Mirabegron in overactive bladder: a review. Urology. 2014;83:1457-1466
- Peters KM et al. Randomized trial of percutaneous tibial nerve stimulation versus extended-release tolterodine. J Urol. 2009;182:1055-1061