Overview
Management of voiding dysfunction in neurologic disorders can substantially improve the quality of life as well as the health of patients. A systematic review of the pattern of voiding dysfunction leads to an understanding of the underlying mechanism, which, in turn, allows the treating physician to develop a strategy for managing it. Neurourology, although a relatively new field of study, has revolutionized the management of a vexing problem that affects millions of patients.
For more information, see Pubovaginal Sling and Injectable Bulking Agents for Incontinence.
Neuroanatomy of Pelvic Floor
Striated muscle forming the urethral rhabdosphincter and the periurethral striated muscle (part of the pelvic diaphragm) together make up the external urethral sphincter mechanism in humans. In women, the rhabdosphincter forms a 1.5-cm long circular ring around the middle third of the urethra, extending cranially as far as the posterior bladder base.[1] In men, the rhabdosphincter has 3 sections extending over a greater length of urethra. On cystoscopy, this striated muscle can be seen to contract with electrical stimulation of the pudendal nerve.
Spinal cord nuclei supplying the vesicourethral smooth muscle and rhabdosphincter are in the lumbosacral region. The sympathetic autonomic nucleus is in the anteromediolateral gray matter at T10-T12, and the parasympathetic nucleus is at S2-S4. Motor neurons of the urethral rhabdosphincter are in the nucleus of Onufrowicz (Onuf) in the sacral ventral horns. The neurons are smaller, more spherical, and more closely packed than other anterior horn cells.
The nucleus of Onuf and the sacral parasympathetic nucleus are at slightly different levels. This can be of clinical significance in lesions of the conus. The neurons of the Onuf nucleus are relatively spared in many neuromuscular disorders.
The somatomotor supply to the rhabdosphincter is via the pudendal nerves. This has been documented by direct stimulation studies and in horseradish peroxidase tracings; however, some studies have shown contributions from some branches of the pelvic plexus. The role of these branches is in question; an autonomic function has been postulated.
In dogs, complete silence of the rhabdosphincter is seen only if the pudendal and pelvic efferents are sectioned. The Onuf nucleus shows changes after injection of horseradish peroxidase into either the pudendal or pelvic nerve. Some evidence suggests that the rhabdosphincter in cats has triple innervation, with cholinergic, adrenergic, possibly co-peptidergic, and traditional motor endplates.
The pudendal nerve leaves the pelvis through the lower part of the greater sciatic notch beneath the lower border of the piriformis muscle. It bifurcates just before the sacrospinal ligament, with one branch going to the anal sphincter and the other to the urethral sphincter. Studies on children with meningomyelocele have suggested that different sacral levels supply the 2 sphincters, so that absence of activity in one is not invariably accompanied by a deficit in the other.
Neurophysiology Of The Pelvic Floor
Sphincter electromyography
Electromyographic (EMG) recordings from the urethral and anal sphincters were first made in the 1930s by Beck,[2] who recorded from the anal sphincter using fine wires. Petersen and Franksson performed studies of the urethral sphincter in 1955.[3]
Since that time, measurements of sphincter activity using conventional electrodes, wires, surface electrodes, and catheter-mounted electrodes have become an important part of the evaluation of the patient with voiding dysfunction.[4] The procedure is not done routinely unless a neurologic basis is suspected as the cause of voiding dysfunction. Some indications would be voiding dysfunction after pelvic or spinal cord trauma and spinal stenosis potentially affecting the cauda equina or conus.
Occasionally, needle EMG may be used to evaluate pelvic pain syndromes. EMG is usually not performed in stress urinary incontinence or when a central nervous system (CNS) lesion is producing the incontinence.
Muscle fibers in the periurethral striated muscle are predominantly type Ia, the slow-twitch, fatigue-resistant fibers. The rhabdosphincter fibers are generally smaller than those of other striated muscle. No stretch receptors have been found in the striated muscle immediately related to the urethra. A curious property of the urethral sphincter is that it has a tonic firing pattern that silences only during voiding.
Positioning of electrodes for recording from the urethral sphincter is performed most easily with the patient in the lithotomy position. The periurethral tissue may be made analgesic with ethyl chloride spray or lidocaine ointment.
The electrode is inserted just lateral to the urethral meatus in women. Sphincter muscle is encountered at a depth of about 15 mm. In the male, the electrode is inserted in the perineum between the scrotum and the anal verge. It may be positioned by feeling for the prostate gland with a finger in the rectum and directing the electrode toward the apex of the gland. The EMG activity should be monitored with a speaker during the positioning.
In females, a 25-mm electrode is used; in adult males, a 75-mm electrode is necessary. If a shorter electrode is used, EMG activity in the more superficial bulbocavernosus muscle is recorded. Other techniques of needle insertion include placement under cystoscopic control and placement via a vaginal approach in women. Although some discomfort is associated with insertion, it is short lived. Most patients tolerate the procedure if well prepared. The author prefers to use monopolar needle electrodes.
At rest, continuous baseline activity consists of motor unit potentials of 100-500 microvolts (?V) firing at rates of 1-4 per second. This activity is at its lowest when the patient’s bladder is empty. As the bladder fills, the firing rate increases slowly until bladder fullness is perceived. At that point, the type II fibers are contracted voluntarily in a graded way. When bladder capacity is reached, some voluntary units of as much as 3 millivolts (mV) are seen.
Continued at resource.
Read More: Urological Management in Neurological Disease