Bladder storage and emptying requires continual coordination of the detrusor and external urinary sphincter (EUS), both mediated by the central and peripheral nervous systems [1–3]. Neurological conditions, lesions or trauma can cause disturbances in urinary storage and voiding resulting in bladder dysfunction. Detrusor sphincter dyssynergia (DSD) is defined by the ICS as ‘the impaired coordination between detrusor and sphincter during voiding due to a neurologic abnormality (i.e. detrusor contraction synchronous with contraction of the urethral and/or periurethral striated muscles)’. DSD is also known as detrusor striated-sphincter dyssynergia and detrusor external-sphincter dyssynergia . Neurological conditions more commonly resulting in DSD include: SCI, MS, spinal dysraphism and transverse myelitis [2,5–12]. In the absence of neurological abnormality, impaired coordination of bladder contraction and sphincter relaxation is more appropriately referred to as dysfunctional voiding or pelvic floor hyperactivity [3,13].
During normal filling, the pelvic nerve afferents are modulated by sympathetic output to cause relaxation of the detrusor while maintaining the tone of the bladder neck sphincter. There is tonic activity of the EUS facilitated by input from the pontine micturition centre (PMC). During voluntary micturition, the inhibitory signals from the frontal cortex to PMC are removed thus allowing activation of the micturition reflex. The PMC inhibits the spinal guarding reflexes and transmits excitatory signals to the bladder [1–3]. The EUS relaxes with synergistic contraction of the detrusor for a coordinated decrease in urethral pressure and rise in detrusor pressure to allow the outflow of urine [1–3].
DSD occurs in the setting of neurological abnormalities between the PMC and sacral spinal cord [1–3,5]. This interruption of the spinobulbospinal pathways is thought to result in failed inhibition of spinal guarding reflexes, erroneous excitation of Onuf's nucleus causing EUS contraction to occur during detrusor contraction, generating elevated detrusor pressures [1,3,5]. Up to 50% of patients with DSD develop serious urological complications [5,14]. Untreated DSD has been associated with reduced bladder compliance, elevated upper tract pressures, VUR, hydronephrosis and renal failure [3,5,14,15]. Complications of DSD occur less frequently in women and patients with MS, perhaps due to lower detrusor pressures [3,9,10].
The precise incidence of DSD is unknown given the variability in neurological disease. SCI contributes to a significant portion of cases of DSD. One report estimates that ≈75% of patients with suprasacral SCI have DSD . The incidence of DSD in MS and spinal dysraphism is estimated at 25–50% [9,10,12].
DSD may present with mixed storage and voiding symptoms, urinary incontinence or complications of DSD, i.e. UTIs and bladder calculi [5,14–16]. Neurological symptoms may predominate and trigger the initial neurourological investigation.
HISTORY AND PHYSICAL EXAMINATION
Comprehensive history and physical examination are essential. Evaluation should not only aim to diagnose the cause and nature of bladder dysfunction but also identify associated complications . History in patients with voiding dysfunction and underlying neurological disease should assess for changes in urinary, bowel and neurological symptoms, as well as disease duration, severity, prior investigations and treatments . Screening for occult neurological disease should be performed in patients with voiding dysfunction and may include inquiry regarding visual changes, back or neck pain, weakness, paraesthesia, urinary or bowel symptoms .
General appearance, hygiene, cognition, mobility and functional status can be helpful in diagnosis and management. Abdominal examination should assess for palpable bladder, constipation, tenderness and previous incisions. Genitalia should be inspected for abnormality and skin irritation. In addition to assessment of the prostate, a DRE is necessary to assess anal sphincter tone at rest and during voluntary contraction . Testing perineal sensation, bulbocavernosus reflex and cremasteric reflexes are part of a complete neurourological examination . Bulbocavernosus reflex tests the sacral nerve reflex arc (S2–S4) and can be confirmed by an increase in anal tone with squeezing the glans penis/clitoris or gently tugging an indwelling urethral catheter . DSD appears to progress and worsen over time making routine and long-term follow-up essential .
Basic laboratory and imaging studies are necessary to monitor renal function and screen for associated urological complications. Urine culture and sensitivity should be performed if there is a suspicion of UTI. Serum electrolytes, urea and creatinine should be monitored [2,5]. Voiding diaries can be helpful in characterising voiding dysfunction, as well as compliance to bladder management regimes, e.g. clean intermittent catheterisation [5,13]. Ultrasonography is helpful for the assessment of hydronephrosis, urinary calculi and post-void residual urine volumes .
Urodynamics play a critical role in the detection of DSD and monitoring for associated complications . DSD can be diagnosed using electromyography (EMG), voiding cystourethrogram (VCUG) and/or urethral pressure profilometry [13,18].
Diagnosis of DSD by EMG requires elevated ‘EMG activity during detrusor contraction, in the absence of Valsalva and Crede manoeuvres’[13,18]. Diagnosis of DSD with EMG is poorly standardised with variance in the type of needle, needle vs patch electrode and electrode placement [13,18]. Patch electrodes are often preferred for easier placement, patient tolerance and allow greater mobility . EMG findings in DSD have been classified into three types by Blaivas [3,5,16].
1Type 1 DSD, there is a progressive increase in EUS contraction activity that peaks at maximal detrusor contraction followed by sudden relaxation of the EUS as the detrusor pressure declines allowing urination [3,5,16].
2Type 2 DSD, clonic contractions of the EUS occur intermittently during detrusor contraction causing intermittency of the urinary stream [3,5,16].
3Type 3 DSD occurs with continuous EUS contraction throughout the entire detrusor contraction resulting in urinary obstruction or inability to urinate [3,5,16].
More recently, Weld et al.  has simplified the classification by dividing DSD into two groups continuous vs intermittent. Both classification systems are presently used. DSD type and degree of SCI lesions seem to correlate . Type 1 DSD occurs in patients with incomplete neurological lesions whereas types 2 and 3 occur more often in patients with complete lesions . Patients with continuous EUS activity during voiding have increased incidence of urological complications probably because of the continuous bladder outflow obstruction throughout the detrusor contraction [3,5,16,17].
Figure 1 is an example of urodynamic tracing with EMG demonstrating type 2 or continuous DSD.
As EMG is not universally available, diagnosis is often made by VCUG. Typical findings include: a closed bladder neck during filling and subsequent dilation of the bladder neck and proximal urethra to the level of the EUS during micturition [13,18]. Figure 2 is an example of a paediatric patient with SCI with DSD showing the dilated posterior urethra and bladder neck on VCUG during bladder contraction.
The role of urethral pressure profilometry in diagnosis of DSD is controversial, and is considered by the ICS to be investigational .
Unfortunately, a perfect test for DSD does not exist. Pathology such as BOO, Parkinson's disease and dysfunctional voiding should be considered before diagnosis, as they may have similar symptomatology. Pseudodyssynergia is the presence of EUS contraction occurring during micturition that may be misinterpreted for DSD . Causes of pseudodyssynergia may include: abdominal straining, attempted inhibition of detrusor contraction or in response to pain . Diagnostic discrepancy between EMG and VCUG ranges from 40% to 46% [13,18]. Males were more often diagnosed with EMG whereas females were more often diagnosed by VCUG [13,18]. It has been suggested that the diagnosis of DSD in males by VCUG may be impaired due to anatomical BOO by the prostate and that in the female diagnosis by EMG may be impaired due to increased electrode artefact . Detection of DSD can be improved by using both EMG and VCUG [13,18]. The clinician should be present during the urodynamic study to increase the accuracy of diagnosis .
Intermittent catheterisation combined with anticholinergics to reduce detrusor pressures is the most common treatment for DSD. Although several medications such as α-blockers and benzodiazepines have been tried, pharmacotherapy has a limited role in the management of DSD [2,3,15]. Inability to catheterise and/or development of complications arising from DSD may lead to more aggressive interventions [2,3,5,15]. Common treatments used include: external sphincterotomy, intrasphincteric injection of botulinum type A toxin and urethral stents [2,3,5,15]. Urinary incontinence in DSD is often managed with a condom catheter in males but no satisfactory external collection device exists for females [2,5]. Failure of these therapies may require long-term indwelling urinary catheterisation, urinary diversion or in specialised centres, dorsal root rhizotomy with sacral anterior nerve root stimulation may be considered [5,15]. As DSD often worsens over time and the chronological course of many neurological conditions are unpredictable, routine life-long follow-up is required to prevent complications and preserve renal function [8,17].
DSD is frequently associated with suprasacral neurological pathology, and has been shown to cause significant morbidity if unrecognised or inadequately managed. High index of suspicion, thorough history and clinical examination are necessary to ensure an accurate diagnosis. Urodynamics using both VCUG and EMG for diagnosis of DSD increases the diagnostic success compared with using either method alone [13,18]. All patients known or at risk for DSD require long-term follow-up to avoid associated complications [8,17].