*Jan Namysł, Krystyna Garstka-Namysł
The use of electromyography in the diagnosis and treatment of anal sphincter dysfunctions
Zastosowanie elektromiografii w diagnostyce i terapii zaburzeń czynności zwieraczy odbytu
INNOMED – A Centre for the Treatment of Paresis in Poznań
Prawidłowa czynność zwieraczy odbytu zależy w dużej mierze od integralności i sprawności struktur układu nerwowego, zaangażowanego w proces kontroli utrzymania stolca i gazów oraz zgodnego z fizjologią i wolą opróżniania jelit. Uszkodzenia i choroby układu nerwowego zaburzają czynność bioelektryczną zwieraczy, której ocena ma istotne znaczenie dla kształtowania procesu leczenia i jego rezultatów. Metodą z wyboru służącą ocenie czynności bioelektrycznej mięśni jest elektromiografia, jedyna obiektywna metoda oceny ich napięcia spoczynkowego, zdolności do utrzymania skurczu oraz terapii EMG-biofeedback. Zebrane w badaniu EMG informacje znacznie przyspieszają proces diagnostyczny i moment wdrożenia skutecznego leczenia. Jeżeli badanie ujawnia neurogenne podłoże zaburzeń zwieraczowych, konieczne jest wdrożenie procesu rehabilitacji. Metodami leczenia neurogennych zaburzeń defekacji i inkontynencji stolca lub gazów są głównie zabiegi elektrostymulacji zwieraczy i/lub ćwiczenia biofeedback, realizowane przez chorych w domu, po przeszkoleniu w gabinecie. Przebieg rehabilitacji powinien być monitorowany w kontrolnych, okresowych badaniach EMG.
Proper function of the anal sphincters largely depends on the integrity and efficiency of neural structures involved in controlling the maintaining stool and gas continence and compliant with the physiology and an individual’s will to empty the intestines. Nervous system disorders and injuries disrupt the bioelectrical activity of anal sphincters, the evaluation of which is important for both the treatment process and its outcomes. Electromyography, which is the only objective approach for assessing resting tone, the ability to maintain sphincter contraction and EMG biofeedback therapy, is the method of choice for assessing the bioelectrical activity of muscles. Electromyographic data significantly accelerate the diagnostic process and effective treatment implementation. If neurogenic aetiology of sphincter disorders is found, it is necessary to implement the rehabilitation process. The therapeutic approaches for neurogenic bowel dysfunction and stool or gas incontinence mainly include sphincter electrostimulation and/or biofeedback exercises, performed by patients at home, after training in the doctor’s office. The course of rehabilitation should be monitored as part of periodic follow-up EMGs.
Dysfunctions of pelvic muscles involved in ensuring proper bowel movement and maintaining stool and gas continence may have a complex aetiology and accompany many diseases, therefore they require detailed diagnosis in order to implement targeted treatment. The most common causes of functional disorders include damage to the key muscles and nerves ensuring stool and gas continence caused by perineal incision or rupture during childbirth, mechanical trauma to the perineum or the anus itself during accidents, as well as iatrogenic injuries as a result of pelvic procedures (1), radiotherapy of the pelvic floor, damage to peripheral or central nervous structures as a result of neurodegenerative diseases (2), congenital atresia of the anus, dystrophic defects, Hirschsprung’s disease, as well as improper eating or bowel movement habits (3). Spinal injuries and degeneration or congenital spinal defects have a significant impact on pelvic muscle activity. L4/5, followed by L3/L4, L5/S1 are the most common levels of hernia, sequestration or prolapse of the nucleus pulposus causing sphincter disorders, whereas the thoracic and cervical segments are much less likely to be involved (4). Complete paralysis of the anal sphincters and the bladder may occur as a consequence of spinal injuries, cauda equina syndrome, weight lifting during a bend or sudden movement, or trauma to the lumbar region (5). The aetiology of sphincter disorders is much less commonly reported and includes epidural haematoma, infections, primary and metastatic tumours or chiropractic manipulations. Both diagnosis and rehabilitation of patients with neurogenic sphincter dysfunctions are neglected. However, many of them can be effectively treated and relieved from the manual rectal emptying or bladder catheterization. Pelvic muscle or sphincter injuries, neoplastic and atrophic lesions, organ prolapse, fistulas or abscesses require surgical intervention or radiotherapy, as in accordance with indications. However, injuries, surgical interventions and radiotherapy are always associated with some damage to the nervous system, neurons or axons and modify their synapses, which affects bioelectrical muscle activity. Electromyography (EMG) is the only tool to assess these changes, which are of great yet underestimated clinical importance. EMG accelerates the diagnosis and allows for the choice of rehabilitation methods.
Sudden events causing injuries to the pelvic muscles or their nerve structures are reported only for some of the patients with stool incontinence.
A significantly larger proportion of patients develop sphincter disorders due to an overlap of several different causes: damage to the muscles and nerves of the pelvic floor as a result of pregnancy or labour, lifting heavy objects, lack of physical exercise, working in a sedentary position, spinal degeneration, improper diet, overweight, and recurrent constipation. Their cumulative effect contributes to undesirable muscular, nervous and vascular modifications in the pelvic floor, which often develop slowly over months or even years. Difficulties passing urine and stool or incontinence gradually intensify. These disorders are often accompanied by spinal pain, sciatica, pelvic pain, a feeling of incomplete bowel movements, or perianal moisture. Anal sphincter dysfunctions are a source of embarrassment for patients, who find it difficult to talk about them or even acknowledge their existence. They are initially marginalised and treated with home remedies or panty liners by the patients themselves. Older individuals often do not attempt any treatment wrongly convinced that sphincter dysfunction is “age related” and “one must learn to live with it” after the age of 70 years. Such misconceptions are detrimental. In our practice, we encounter many patients over the age of 80 years with problems limited to the bladder or anal sphincters. The causes of sphincter insufficiency diagnosed in EMG in these patients belong to the group mentioned above rather than being age-related. The outcomes of stimulation and exercises performed by patients at home, after completing an in-office training, prove that specialist proctological rehabilitation can improve sphincteric function and the quality of life at any age. Motor disabilities or cognitive disorders are the only serious obstacles in introducing the patient to systematic interventions. Due to the frequent embarrassment and the above mentioned misconceptions, patients are usually motivated to see a specialist only by an advanced stage of the disease, stool and gas incontinence, or chronic constipation. Consulting stool/gas incontinence or constipation with a doctor initiates treatment attempts using dietary and lifestyle modifications, as well as laxatives (6, 7). However, the above-mentioned approaches prove insufficient in the case of neurogenic disorders causing abnormal muscle tone or discoordination of the muscles responsible for continence and proper bowel movement. There is no scientific evidence that they induce reinnervation or improvement of synaptic function, regeneration of myelin, motor neurons or damaged cells of Cajal (8). They do not allow either for the strengthening of paralysed muscles, or the restoration of nervous control ensuring proper sphincter activity. Damage to the axons of peripheral nerves, their demyelination, and impaired nerve conduction negatively affect the reorganisation of synaptic connections both in the central nervous system and in the sacral plexus, as well as the bioelectrical muscle activity. Surgical procedures, perineoplasty and restoration of anal sphincter are not sufficient to ensure effective neural control over the bowel contents to prevent incontinence or constipation. Its restoration requires interventions that go beyond surgery. These interventions should be preceded by an objective EMG assessment of pelvic muscles, and rehabilitation focusing not only on sphincter activity, but also on the improvement of spinal function and education should be the method of treatment.
Neural sphincter control
Elevated intra-abdominal pressure translates into an increased contractile activity of all urogenital diaphragm muscles, ensuring simultaneous urinary and faecal continence. The pelvic muscles and the intrapelvic fascia provide anatomical support for the pelvic floor organs, including the rectum, bladder and anal sphincters. Due to their supporting functions, they are mainly composed of oxygen-metabolizing slow-twitch (S-type) fibres requiring adequate blood supply. These fibres are innervated by thin motor nerve axons prone to injury. Damage to the sphincteric innervation or its impaired blood supply cause deterioration or loss of control over bowel movements (9). Neural control of sphincteric functions is multi-level and highly complex. Motor, sensory and autonomic fibres are involved in pelvic innervation. Pelvic smooth muscles and glands are innervated by the pelvic autonomic system, which consists of the sacral part of the sympathetic trunk, pelvic branches of the sympathetic trunk, the pelvic parasympathetic visceral nerves and the inferior hypogastric plexus.
The striated muscles, skin and organs are sensorially innervated by the branches of the sacral plexus (10). The external anal sphincter (EAS) is innervated by the voluntarily controlled mixed somatic pudendal nerve. It consists of motor and sensory nerves S2-S4 as well as the sympathetic and parasympathetic fibres. Neurons in the sympathetic and parasympathetic ganglia receive a signal from the preganglionic neurons located in the central nervous system (CNS). The sympathetic preganglionic fibres are located in the middle thoracolumbar spinal cord (11).
While the EAS is individually innervated by the inferior rectal nerves, its contractile activity is closely related to the activity of the neighbouring groups of levator ani muscles and the puborectalis muscle innervated by the pudendal and coccygeal nerves, as well as the activity of smooth bowel muscles (12). The coordination of this activity is controlled by complexes of multiple interneurons that integrate the activity of neurons. Some of them are found in the brain and spinal cord, while other are located in the autonomic ganglia. Weakening or loss of individual types of interneurons may result in discoordination of muscle activity and neuropathic pain due to the lack of inhibition of nociceptive stimuli (13). The intestinofugal neurons, whose cellular bodies are located in the Auerbach’s plexus, are also important in controlling local reflexes. They receive the input signal from local intestinal neurons and connect with sympathetic motor neurons in the prevertebral ganglia (14). The activity of neuronal centres for controlling pelvic muscle tone depends on sensory information triggering reflex responses, but is also strongly influenced by consciousness, which under normal conditions plays a fundamental role in determining the time of bowel emptying. In response to a command generated in the brain, both a significant delay in the visit to the toilet and relaxation of anal sphincters, the puborectalis muscle and the levator ani are possible as a result of intentional inhibition of motor neuron activity. The consciously controlled somatically innervated external sphincter activates peristaltic movements through the interneuronal connections of somatic and autonomic nerves, enabling defecation. The external sphincter acts as a consciously controlled switch.
This happens only with proper coordination, in individuals with normal bowel activity. Discoordination of this mechanism occurs in habitual or neurogenic abnormal (usually increased) resting sphincteric tone. As a result of disturbed activity of motor neurons and synapses in some patients, the increased tone is processed by interneurons as a deliberate attempt to stop bowel movement, which seriously disturbs or even prevents peristaltic activity. A tendency to constipations develops. However, persistently increased tension compromises muscle ability to generate effective contraction and leads to the loss of control over bowel contents, as a result of impaired blood supply and depletion of mitochondrial energy. Both these situations require rehabilitation using both electrostimulation and biofeedback exercises. Neither of these methods is superior to the other as each has its own indications and limitations. Electrostimulation is used for reinnervation and normalisation of the bioelectric activity of muscles and is essential in all neurogenic sphincter disorders. Biofeedback plays a role in neuromuscular re-education and is mainly used on an outpatient basis, during visits and at-home therapy in patients with normal ability to generate muscle tone, but presenting with instability, discoordination and abnormal relaxation. Both methods have been known and used for years in the treatment of incontinence, and their positive role has been confirmed in multiple randomised clinical trials (15-17).
Objective assessment of anal sphincter tone
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