Causes of Overactive Bladder
Overactive bladder (OAB) is primarily caused by detrusor overactivity, characterized by involuntary contractions of the bladder muscle during the filling phase, though the exact underlying mechanisms are multifactorial and not completely understood. 1
Definition and Key Symptoms
- OAB is defined by the presence of urinary urgency (a sudden, compelling desire to pass urine that is difficult to defer) as the hallmark symptom 1
- OAB typically includes urinary frequency (more than seven micturitions during waking hours) 2, 1
- Nocturia (interruption of sleep due to the need to void) is commonly present in OAB patients 1
- Urgency urinary incontinence may or may not be present, defined as involuntary leakage associated with urgency 2, 1
Primary Causes of OAB
Neurogenic Causes
- Neurological diseases or injuries affecting central or peripheral nervous system control of the bladder 2
- Abnormal processing of sensory information in the central nervous system 3
- Emergence of new voiding reflexes following neurological damage 4
Myogenic Causes
- Increased excitability of bladder smooth muscle 3
- Abnormal spread of excitation through the bladder wall 3
- Detrusor muscle instability leading to spontaneous contractions 2
Sensory/Afferent Causes
- Increased sensory nerve activity from the bladder 3
- Hypersensitivity of bladder sensory pathways 1
- Altered sensory processing in the central nervous system 3
Contributing Factors and Secondary Causes
- Bladder outlet obstruction (particularly in men with prostatic enlargement) 2, 4
- Urethral weakness or incompetence 4
- Aging-related changes in bladder function 5, 3
- Detrusor hyperactivity with impaired contractility in elderly patients 4
Conditions That Must Be Ruled Out
- Urinary tract infection (UTI) 2
- Hematuria not associated with infection 2
- Nocturnal polyuria (excessive nighttime urine production) 2, 1
- Neurological disorders directly affecting bladder function 2
- Medication side effects that may affect bladder function 2
- Overflow incontinence due to urinary retention 6
Diagnostic Considerations
- OAB is a diagnosis of exclusion requiring careful history, physical examination, and urinalysis 1
- Post-void residual (PVR) assessment should be performed in patients with obstructive symptoms, history of incontinence or prostatic surgery, and neurologic diagnoses 2
- Antimuscarinic medications should be used with caution in patients with PVR 250-300 mL 2, 6
- Bladder diaries are useful for documenting voiding patterns and distinguishing OAB from other conditions 2, 7
Common Pitfalls in Diagnosis
- Failure to distinguish between mixed urinary incontinence and pure OAB can lead to inappropriate treatment 1
- Misdiagnosing overflow incontinence as OAB may lead to worsening symptoms with antimuscarinic treatment 6
- Not considering medication side effects as potential contributors to bladder symptoms 6, 7
- Inadequate evaluation of nocturia, which may be due to factors unrelated to OAB such as sleep disorders or cardiovascular disease 2, 1
Understanding the complex and multifactorial nature of OAB is essential for proper diagnosis and management, as treatment approaches will vary depending on the underlying mechanisms and contributing factors 8.