What causes Overactive Bladder (OAB)?

What Causes Overactive Bladder (OAB)

In the majority of cases, OAB is idiopathic—meaning no identifiable cause is found after systematic evaluation to exclude neurological, obstructive, or other pathological conditions. 1

Primary Mechanisms

OAB arises from three main pathophysiological mechanisms that can occur independently or in combination:

• Myogenic causes: Detrusor muscle instability leading to spontaneous contractions is a primary mechanism 1, 2
• Neurogenic causes: Neurological diseases or injuries affecting central or peripheral nervous system control of the bladder contribute to OAB 1, 3
• Urotheliogenic causes: Altered sensory and barrier functions of the urothelium can trigger OAB symptoms 2

The American Urological Association emphasizes that when no identifiable neurological, obstructive, or other pathological cause is found after appropriate evaluation, the diagnosis is idiopathic OAB, which represents the majority of OAB cases in clinical practice 1, 4.

Secondary and Contributing Causes

Obstructive Causes

• Bladder outlet obstruction, particularly in men with prostatic enlargement, can contribute to OAB 1
• Pelvic organ prolapse in women can cause bladder outlet obstruction and exacerbate OAB 4

Neurological Conditions

Multiple neurological diseases can cause OAB symptoms, including:

• Multiple sclerosis and related neuroinflammatory disorders 3
• Parkinson's disease 3
• Multiple system atrophy 3
• Spinal cord injury 3
• Dementia 3
• Peripheral neuropathy 3

Age-Related and Hormonal Factors

• Age-related changes in bladder function are common, though OAB is not a normal consequence of aging 4, 5
• Genitourinary syndrome of menopause is a recognized comorbidity that can worsen OAB symptoms in women 4

Metabolic and Systemic Factors

• Metabolic derangement can increase the excitability of nerve and detrusor muscle 2
• Inflammation can alter sensory and barrier functions of the urothelium 2
• Diabetes mellitus can contribute to OAB severity 4

Exacerbating Factors

Several modifiable factors worsen OAB symptoms:

• Obesity: Weight loss of 8% reduces urgency incontinence episodes by 42% vs. 26% in controls 4
• Constipation can affect OAB severity 4
• Diuretic use can exacerbate symptoms 4
• Bladder stimulants (caffeine, alcohol) increase symptom burden 6

Critical Conditions That Must Be Excluded

OAB is fundamentally a diagnosis of exclusion. 1, 4 Before diagnosing idiopathic OAB, systematically rule out:

• Urinary tract infection: Requires urinalysis and culture if indicated 1, 4
• Hematuria not associated with infection: Mandates urologic evaluation 1, 4
• Nocturnal polyuria: Distinguished by normal or large volume nocturnal voids, unlike the small volume voids in OAB 1, 4
• Medication side effects: Comprehensive medication review is essential 4
• Urinary retention/overflow incontinence: Evaluate with post-void residual measurement in patients with emptying symptoms, history of retention, prior incontinence surgery, or long-standing diabetes 4, 7

Common Diagnostic Pitfall

Failure to measure post-void residual in appropriate patients can lead to misdiagnosing overflow incontinence as OAB, resulting in inappropriate antimuscarinic treatment that worsens the underlying condition. 4, 7 PVR should be performed in patients with concomitant emptying symptoms, history of urinary retention, prior incontinence surgery, or long-standing diabetes 4. Antimuscarinics should be used with caution in patients with PVR 250-300 mL 4, 7.