Causes of Detrusor Underactivity
Detrusor underactivity (DU) has multiple etiologies including diabetes mellitus, neurological disorders, aging, bladder outlet obstruction, and pelvic nerve injuries, all of which can lead to impaired contractility of the bladder muscle. 1
Definition and Clinical Presentation
Detrusor underactivity is defined as a contraction of reduced strength and/or duration, resulting in prolonged bladder emptying and/or failure to achieve complete bladder emptying within a normal time span 2. Clinically, it presents with:
- Prolonged urination time
- Sensation of incomplete bladder emptying
- Hesitancy
- Reduced sensation on filling
- Slow urinary stream
- Often accompanied by storage symptoms
Major Causes of Detrusor Underactivity
1. Neurological Disorders
- Spinal Cord Malformations: Tethered cord and other dysraphic malformations can cause detrusor underactivity 3
- Peripheral Neuropathy: Damage to peripheral nerves affecting bladder innervation
- Central Nervous System Dysfunction: Affecting central control of micturition
2. Diabetes Mellitus
- Diabetic cystopathy occurs in up to 80% of type 1 diabetic patients 3
- Leads to impaired detrusor contractions and increased post-void residual (PVR) volume
- Urodynamic findings include impaired bladder sensation, increased cystometric capacity, and decreased detrusor contractility 3
3. Aging-Related Changes
- Myogenic failure with aging
- Axonal degeneration
- Muscle loss and fibrosis in the detrusor 2
4. Bladder Outlet Obstruction
- Chronic obstruction can lead to detrusor decompensation
- May be the clinical endpoint for some patients in whom urge incontinence leads to dysfunctional voiding, high pressure bladder, and finally detrusor decompensation 3
5. Mixed Disorders
- Detrusor Hyperactivity with Impaired Contractility (DHIC): Common in elderly, presents with both overactive bladder symptoms and impaired emptying 2
- Dysfunctional Voiding with Detrusor Underactivity: Coexistence can result in episodes of urgency, urge incontinence, and incomplete bladder emptying 3
Pathophysiological Mechanisms
Several contributing factors have been identified in the pathophysiology of detrusor underactivity:
Myogenic Failure:
- Detrusor muscle degeneration
- Reduced contractility due to changes in muscle properties
Neurogenic Factors:
- Efferent Dysfunction: Impaired motor innervation to the detrusor
- Afferent Dysfunction: Reduced bladder sensation and impaired afferent signaling
- Abnormal perineal electrophysiological testing in diabetic patients 3
Reduced Bladder Sensation:
- Closely associated with low detrusor contractility 4
- May lead to bladder overdistention and further deterioration
Diagnostic Considerations
Diagnosis of detrusor underactivity is challenging as symptoms lack adequate precision 2. Urodynamic studies remain the gold standard:
- Impaired bladder sensation
- Increased cystometric capacity
- Decreased detrusor contractility
- Increased post-void residual volume
- Low maximum flow rate and prolonged voiding time
Clinical Implications
The presence of detrusor underactivity significantly impacts treatment outcomes:
- Patients with intact detrusor contractility (either low or normal voiding pressure) have better treatment outcomes (69.2-81.8% success) 4
- Patients with detrusor acontractility (41.3%) or absent bladder sensation (17.9%) have less favorable outcomes 4
- Management of individuals with DHIC remains challenging as anticholinergic medications may worsen retention 2
Conclusion
Detrusor underactivity represents a complex, multifactorial condition with significant clinical impact. Understanding its diverse etiologies is essential for appropriate diagnosis and management, particularly in populations at higher risk such as diabetic patients, the elderly, and those with neurological disorders.