Interference pattern in perineal muscles: a quantitative electromyographic study in patients before and after transurethral surgery of the prostate

The study aimed at assessing alterations in muscular activity in the external urethral sphincter when the internal sphincter located at the bladder neck was resected during TUR-P, and at determining whether activity in the external urethral sphincter increased to compensate for the loss of the internal sphincter. Perineal muscles were examined with quantitative EMG recordings, including interference pattern and fiber density before and after surgery. Fiber density increased in the external urethral sphincter after surgery. This indicates a reinnervation in the muscle, probably due to a peripheral nerve lesion that occurs during TUR-P, and may also explain the reduction in penile erectibility observed after surgery. The lack of compensatory activity in the external urethral sphincter expressed as unchanged number of turns may be explained as a disturbed feedback mechanism and a decreased central activation or to the lithotomy position at examination. The internal part of the external sphincter not available for measurement may compensate for the loss in bladder-neck sphincter function.

Dynamic bulbocavernosus reflex: dyssynergia evaluation following SCI

High urethral resistance caused by detrusor-sphincter dyssynergia (DSD) occurs following spinal cord injury (SCI) and results in poor voiding. A major pelvic floor reflex that may be involved in DSD is the bulbocavernosus reflex (BC) and evaluation of this reflex during the micturition cycle may provide additional information regarding this role. The periodic BC observed during micturition via cystometry is described as a dynamic bulbocavernosus reflex (DBC). The DBC was induced in upper motor neuron SCI patients using periodic dorsal penile nerve stimulation; the evoked reflex response was recorded with an anal sphincter pressure sensing balloon. Stimulation of 15-50 mA was applied at the base and dorsal side of the penis with surface electrodes, pulsed at a rate of 0.25 Hz. By applying the stimulation during cystometry, the BC reflex could be evaluated throughout the entire micturition cycle. Results showed that the DBC increased during bladder filling and bladder contractions. These findings indicate that an enhanced BC reflex is a major factor causing increased urethral resistance during micturition.