Electromyography should be recorded throughout the urodynamics test including bladder filling, provocative maneuvers and during voiding. The patient without neurological sequalae should be able to show an increase in EMG tracing during a cough or valsalva maneuver (Fig. 2). Although common, not all patients will be able to recruit pelvic floor musculature (and hence increase EMG signal) when asked to perform a volitional Kegels exercise. In fact, several studies have shown that 30–70 % of patients may not be able to recruit their pelvic floor musculature when volitionally asked [24, 25].

During bladder filling, the EMG signal should stay relatively quiet and consistent. You may note a slight increase in resting EMG tone throughout bladder filling, a process called recruitment or the guarding reflex [26]. This reflex may be heightened in spinal cord injured patients (Fig. 3).

During normal micturition, EMG activity disappears completely for a few seconds before a detrusor contraction starts. This is coordinated in response to neuromodulation by the pontine micturition center. The EMG signal then resumes once the bladder is empty [26]. However, in a secondary analysis of urodynamic and EMG data from the SISTEr trial, quantitative and qualitative EMG signals during urine flow were usually greater than during fill. There did not seem to be a correlation to post operative voiding dysfunction and higher preoperative EMG activity. The authors noted that in this group of women, perineal surface patch EMG did not measure the expected pelvic floor and urethral sphincter relaxation during voiding [27].

Electromyography testing may be most helpful in those patients with neurogenic disorders as it is useful to assist in the diagnosis of detrusor external sphincter dyssynergia that is characterized by an involuntary contraction of the external sphincter during detrusor contraction. This is characterized by an increase in EMG signal during the micturition phase associated with a detrusor contraction. It is commonly seen in suprasacral spinal cord lesions such as spinal cord injury, multiple sclerosis, thoracic myelomeningocele, transverse myelitis, and other lesions that interfere with neuromodulation from the pontine micturition center. Detrusor sphincter dyssynergia, if not managed appropriately, may have negative effects of both the upper and lower urinary tract, the extent of which is beyond the scope of this chapter.

Blaivis described three types of detrusor sphincter dyssynergia (DSD) Type 1 DSD (Fig. 4), demonstrated in 30 % of his study population, was characterized by a crescendo increase in EMG activity that reached a maximum at the peak of the detrusor contraction. Type 2 DSD (Fig. 5) consisted of clonic sphincter contractions interspersed throughout the detrusor contraction and type 3 DSD (Fig. 6) (55 % of his study population) was characterized by a sustained sphincter contraction that coincided with the detrusor contraction. No correlation was noted to spinal cord injury level (all were suprasacral) and pattern of DSD.

It is important to consider that some volitional behaviors such as recruitment of pelvic floor due to pain or discomfort (Fig. 7), an increase in EMG signal in response to valsalva/Crede voiding or any other source of artifact (fluid on patch, etc.) may mimic detrusor sphincter dyssynergia. Careful attention to these factors during the procedure is important to prevent misinterpretation of the results. It is this authors practice to repeat the test using fluoroscopy (see chapter “The Use of Fluoroscopy ” for more details), if not already in use, if an unexpected increase in EMG signal was noted without any identifiable artifact. Several studies have demonstrated that fluoroscopic images can significant assist in the diagnosis of detrusor sphincter dyssynergia in the setting of a potentially unreliable surface patch EMG electrode [22].

The confirmed, unexpected finding of an increase in EMG signal during micturition should prompt a neurologic evaluation to look for an underlying source such as multiple sclerosis. If no neurologic source is found in the presence of increased sphincter activity with voiding, the diagnosis of dysfunctional voiding or pelvic floor dyssynergia is applied [28]. Dysfunctional voiding is defined as ‘intermittent and/or fluctuating flow rate due to involuntary intermittent contractions of the peri-urethral striated muscle during voiding in neurologically normal individuals’ [29]. Fowlers syndrome is a subgroup of women with dysfunctional voiding that present with urinary retention and often endocrine problems resembling Stein-Leventhal syndrome. These women may show characteristic non-relaxing EMG during voiding or an increase in EMG signal during micturition. There is no identifiable neurologic lesion that can account for the increase in EMG signal [30].

With sacral or infra-sacral denervation injuries such as radial pelvic surgery or sacral myelomeningocele, the urethra may have a fixed, non-relaxing tone. No significant change will be noted on EMG signal during the filling or micturition phases of the urodynamic study.