Detrusor Sphincter Dyssynergia (DSD) is a specific type of lower urinary tract dysfunction characterized by a lack of coordination between the two muscles responsible for the body’s ability to urinate. Normally, the urinary system relies on a synergistic sequence: the detrusor muscle (bladder wall) contracts to push urine out, while the external urethral sphincter relaxes to allow flow. DSD occurs when this synchronized effort fails, meaning the detrusor muscle contracts forcefully at the exact moment the sphincter muscle involuntarily tightens. This simultaneous, opposing action results in a functional blockage of the bladder outlet, preventing the complete and easy passage of urine.
Understanding the Urinary System Failure
DSD creates significant bladder outlet obstruction because the detrusor is contracting against a closed gate. In a healthy body, the central nervous system coordinates sphincter relaxation with bladder contraction to ensure smooth, low-pressure urine flow. When DSD is present, the detrusor generates high pressure in an attempt to overcome the resistance of the tightened sphincter.
This forceful contraction against a closed sphincter leads to symptoms related to incomplete and obstructed voiding. Symptoms include difficulty initiating the stream, interrupted or intermittent flow, and the frequent, ineffective need to strain or push to empty the bladder.
The most significant consequence of this failure is the inability to fully empty the bladder, leading to a high post-void residual volume (PVR). This sensation of incomplete emptying is often coupled with urinary frequency and urgency, as the bladder never truly empties and reaches its storage capacity sooner. High bladder pressure combined with poor emptying can also manifest as reflex incontinence, where urine leaks involuntarily due to the excessive pressure buildup.
Neurological Roots of Dyssynergia
DSD is fundamentally a neurological disorder, not a primary muscle problem, arising from a miscommunication within the central nervous system. The condition is specifically linked to damage in the neural pathways that coordinate the bladder and sphincter, particularly in the spinal cord above the sacral region (suprasacral lesions). This damage disrupts the inhibitory signals that would normally tell the sphincter to relax during bladder contraction.
The most common underlying cause is a traumatic spinal cord injury (SCI), particularly in the thoracic and cervical spine. Other conditions that damage the central nervous system can also lead to this dyssynergia. These include:
- Demyelinating diseases like multiple sclerosis.
- Developmental disorders such as spina bifida.
- Neurological insults like stroke.
- Transverse myelitis.
In all these cases, the neurological injury prevents the brainstem from properly sending the coordinating signals to the lower urinary tract. The bladder reflex remains intact, often causing an overactive detrusor contraction, but the loss of central inhibition means the external urethral sphincter contracts inappropriately.
Confirming the Diagnosis
The definitive diagnosis of Detrusor Sphincter Dyssynergia relies on specialized testing, as clinical symptoms alone can be misleading. The gold standard for confirmation is a comprehensive Urodynamic Study (UDS), often performed with simultaneous fluoroscopy (video-urodynamic study or VUDS). This procedure measures pressures and flow rates in the bladder and urethra during the voiding cycle.
A key component of the UDS is the Pressure Flow Study, which directly demonstrates the bladder’s struggle to empty. This test measures the detrusor pressure while simultaneously measuring the urinary flow rate, showing a high detrusor pressure coupled with an obstructed or low flow rate. This finding is highly suggestive of a blockage at the outlet.
To confirm the obstruction is due to the sphincter, the UDS incorporates Electromyography (EMG), which measures the electrical activity of the external urethral sphincter muscle. The diagnosis of DSD is confirmed when the EMG recording shows an increase in electrical activity, indicating muscle contraction, at the precise time the detrusor is contracting. Imaging techniques like a Voiding Cystourethrogram (VCUG) or ultrasound can also be used during the study to visually confirm the narrowing of the urethra during the bladder’s attempt to empty.
Primary Treatment Approaches
Since Detrusor Sphincter Dyssynergia is a consequence of permanent neurological damage, treatment focuses on managing the condition, protecting the upper urinary tract, and ensuring complete bladder emptying. The primary and most reliable method for managing the high residual urine and pressure is Intermittent Catheterization (IC). This involves the patient or caregiver periodically inserting a thin tube through the urethra to drain the bladder completely, preventing complications associated with chronic urinary retention.
Pharmacological strategies are often employed alongside catheterization to modulate muscle activity. Alpha-blockers, such as tamsulosin, are sometimes prescribed to help relax the smooth muscle fibers in the bladder neck and internal sphincter, reducing resistance at the outlet. Additionally, anticholinergics or beta-3 agonists may be used to calm the detrusor muscle, reducing the intensity of the involuntary and high-pressure contractions.
For more direct relief of the sphincter’s spastic contraction, interventional procedures are available. Botulinum Toxin (Botox) injections into the external urethral sphincter muscle temporarily paralyze the muscle, forcing it to relax. This chemical denervation provides temporary relief from the obstruction, generally lasting several months, and is considered an effective, less invasive option.
When less invasive methods fail to adequately lower bladder pressure, surgical intervention may be considered. Endoscopic urethral sphincterotomy is a procedure that surgically incises the external sphincter muscle to permanently reduce the obstruction. This is typically reserved as a last resort, as it is irreversible and carries risks, including bleeding and the potential for new onset of urinary incontinence.
Preventing Long-Term Health Damage
The most serious risk associated with untreated Detrusor Sphincter Dyssynergia is the development of chronic high intravesical pressure. When the detrusor contracts against a closed sphincter, the resulting pressure can push urine backward toward the kidneys, a process known as vesicoureteral reflux. This backward flow is highly damaging and is the main driver of long-term complications.
Chronic high pressure and incomplete emptying create an environment conducive to recurrent Urinary Tract Infections (UTIs), which can escalate to severe infections like urosepsis. More concerning is the structural damage caused by the constant high pressure, which leads to hydronephrosis, or the swelling of the kidneys due to urine backup. Adherence to management strategies, particularly intermittent catheterization, is therefore paramount to protect the delicate upper urinary tract from this cascade of damage.