What Causes Overactive Bladder?
Overactive bladder results from either neurogenic dysfunction (abnormal nervous system control of the bladder) or myogenic dysfunction (spontaneous detrusor muscle contractions), with bladder outlet obstruction serving as an important contributing factor, particularly in men. 1
Primary Mechanisms
Neurogenic Causes
- Neurological diseases or injuries affecting central or peripheral nervous system control of the bladder represent a major cause of OAB. 1 This includes conditions such as multiple sclerosis, spinal cord injury, Parkinson's disease, and stroke. 2, 3
- The bladder and micturition cycle are under complex neural control involving both sympathetic and parasympathetic nervous systems, and disruption at any level can produce OAB symptoms. 4
- Approximately 50% of multiple sclerosis patients report urinary incontinence, and most spinal cord injury patients develop bladder dysfunction. 2
Myogenic Causes
- Detrusor muscle instability leading to spontaneous, uncontrolled contractions is the primary myogenic mechanism. 1 These unstable bladder contractions occur in the absence of detectable disease and result in the characteristic urgency, frequency, and nocturia. 5
- Myogenic dysfunction may arise from abnormal activation of receptors in the bladder muscle or detection of chemical stimuli by receptors within the bladder lining. 4
Contributing Factors
Bladder Outlet Obstruction
- Bladder outlet obstruction, particularly from prostatic enlargement in men, is an important secondary cause that can trigger OAB symptoms. 1 This mechanism differs from primary OAB and requires specific evaluation with post-void residual measurement. 1
Multifactorial Nature
- The causes of OAB are multifactorial and not completely understood, with many cases representing idiopathic dysfunction where no specific neurological or anatomical cause can be identified. 4
- OAB affects approximately 11-19% of both men and women, with prevalence increasing with age, though it is not a normal consequence of aging. 2, 4
Critical Diagnostic Distinction
OAB is fundamentally a diagnosis of exclusion—the symptoms occur "in the absence of urinary tract infection or other obvious pathology." 6 This means several conditions must be ruled out:
- Urinary tract infection must be excluded through urinalysis. 1
- Hematuria not associated with infection requires investigation. 1
- Nocturnal polyuria (characterized by normal or large volume nocturnal voids) must be distinguished from OAB (which produces small volume voids). 1
- Medication side effects can mimic OAB symptoms and must be considered. 1
Common Pitfall
The most critical error is misdiagnosing overflow incontinence as OAB, which leads to inappropriate antimuscarinic treatment that worsens urinary retention. 7 Post-void residual measurement is essential in patients with obstructive symptoms, history of incontinence or prostatic surgery, and neurologic diagnoses to avoid this dangerous mistake. 1, 7