Faecal incontinence (leakage of stool)

16 Faecal incontinence (leakage of stool)




Case


Mrs C.B. is a 58-year-old woman who presents complaining of worsening faecal incontinence over 2 years. She had noticed soiling of her underclothes two or three times per week and needed to wear a pad. This occurred particularly if the stool was loose but also occasionally with formed stool. She also had incontinence to flatus. The incontinence took the form of urgency, with inability to defer defecation and soiling if she did not make the toilet in time. At other times there was involuntary seepage without awareness.


In terms of risk factors for incontinence, she had three vaginal deliveries, the first being complicated by a third degree tear. She was not aware of haemorrhoidal or rectal prolapse, and there had been no prior surgery for an anal condition.


On digital anorectal examination the sphincter felt weak and the sphincter ring felt intact. There was no external rectal prolapse, or internal prolapse seen at rigid sigmoidoscopy when asking the patient to strain down. Anorectal manometry showed a low resting and squeeze pressure, and normal rectal compliance. Pudendal nerve conduction studies showed delayed conduction along the nerves, and endoanal ultrasound showed a thin sphincter anteriorly, but the sphincter was otherwise complete. The findings indicated neurogenic weakness of the internal and external sphincter as the cause of incontinence.


Management and progress: Mrs B was prescribed psyllium (Metamucil™) and loperamide (Imodium™) to attempt to bulk up the stools and make them more solid. She was given biofeedback treatment to try to strengthen the sphincter muscles. There was no significant improvement in her incontinence. She was then treated with sacral nerve stimulation and had a good result with the test electrode; she then went on to have a permanent stimulator inserted, with good effect.





History


The causes of faecal incontinence are summarised in Box 16.1. A good history about the nature of the incontinence will often provide clues about the cause. Physical examination and tests of anorectal function will determine whether the sphincter is normal, and will identify the likely pathology in most cases. The three most common causes of faecal incontinence requiring surgical treatment are rectal prolapse, sphincter trauma and neurogenic incontinence. These conditions account for the majority of patients who suffer severe longstanding symptoms.



The features in the history that need to be established in these patients are:









Examination


The patient is examined in the left lateral position with the hips flexed to allow the examiner good access to the perineum and anal region. The area is inspected for soiling, and for excoriation of the perianal skin as evidence of chronic irritation secondary to incontinence. Any external prolapse at the anus (Box 16.2) and an asymmetrical sphincter caused by trauma and perianal scarring are looked for.



Digital anorectal examination is carried out next and the resting tone (produced by the internal sphincter) is noted. The functional length of the anal canal in centimetres should be estimated. The strength of the pelvic floor muscles is assessed by pressing posteriorly and laterally. External sphincter strength is assessed by asking the patient to contract the sphincter and, thereafter, to cough. A shortened, weak sphincter is found in neurogenic incontinence. A weak sphincter of normal length is caused by a sphincter defect due to trauma. The sphincter is examined circumferentially between the thumb and index finger and a defect may be palpable.


The rectal mucosa is then examined circumferentially for proctitis or a tumour; this should not be done at the beginning of the examination since discomfort from deep pelvic examination may impair the subsequent ability of the patient to cooperate with contraction and relaxation of the sphincter.


The patient is next asked to bear down while the examiner looks for rectal prolapse. The ischial tuberosities are palpated and the plane of the perineum assessed in relation to the position of an imaginary line drawn between the tuberosities. If the perineum descends below this line when the patient is asked to bear down, this is evidence for abnormal descent associated with neurogenic weakness of the pelvic floor muscles. If rectal prolapse is suspected but not demonstrated in this position, the examination should be repeated with the patient squatting over a paper towel or sitting on a commode.


If there is a history suggestive of a neurological condition, a full neurological examination should be carried out.




Physiological Anorectal Assessment


Before considering physiological investigation of anal incontinence it is important to consider the physiology of continence. Continence is maintained by a complex process that has both sensory and motor components.



Physiology of continence


Normal continence depends on an interaction of the following factors.


The anal canal is surrounded by a muscular tube that produces a high-pressure zone exceeding the pressure in the rectum. The sphincter contains two layers (Fig 16.1): an inner layer of involuntary smooth muscle (internal sphincter) and an outer layer of skeletal muscle (external sphincter). The internal sphincter is a distal continuation of the circular muscle of the rectum and is in a state of constant contraction, maintained by a process of intrinsic muscle stimulation. Relaxation of the muscle occurs during defecation, mediated by a local neural reflex within the wall of the anorectum in response to distension of the rectum by the faecal bolus, as well as by extrinsic autonomic control via the presacral sympathetic nerves. The external sphincter is under voluntary control but also contracts involuntarily in response to an increase in intraabdominal pressure via a spinal reflex through the anterior horns of the S2–S4 spinal segments and the Onuf nucleus in the spinal cord.



The puborectalis muscle lies immediately above the external sphincter and forms a muscular sling behind the anus (Fig 16.2). It supports the anus and produces the anorectal angle, which is felt posteriorly at the upper end of the anal canal when doing a rectal examination.



There are three anal cushions in the 3, 7 and 11 o’clock positions formed from expansions of the submucosa of the anal canal. The cushions are compressed when the sphincter pressure is high, but expand at other times and lie in apposition to each other. They play a small role in assisting to maintain continence.


The anal mucosa contains an abundance of sensory nerve endings. Spontaneous relaxation of the upper part of the internal sphincter occurs intermittently to allow the anal mucosa to ‘sample’ the contents of the rectum (the sampling reflex). This allows us to normally distinguish flatus from stool in the rectum.


The consistency of the stool in the rectum has an important influence on continence, a fact often overlooked.


The rectum is a storage organ and its wall must be compliant in order to fulfil this reservoir function. Diseases affecting the rectal wall may make it less compliant and impair continence.



Diagnostic tests



Anorectal manometry


Pressure in the anus and rectum is measured using a narrow diameter multichannel catheter. Each channel is perfused with water and connected to a pressure transducer and digital recording apparatus; sequential channels open at 0.75 cm intervals from the tip of the catheter (Fig 16.3). The pressure at rest reflects the strength of the internal sphincter, and pressure during voluntary contraction of the muscles is a measure of the external sphincter strength (Fig 16.4). Relaxation of the internal sphincter is tested by inflating a balloon positioned in the rectum at the tip of the manometry catheter, while recording anal pressure. Manometry is a very useful test because it defines which muscle is affected in a patient with sphincter weakness. It also demonstrates that sphincter function is normal in a patient whose incontinence is due to diarrhoea or excessive colonic propulsion, or due to a local anal condition such as haemorrhoids and, hence, confirms that sphincter weakness is not the cause of the incontinence.

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May 30, 2016 | Posted by in GASTROENTEROLOGY | Comments Off on Faecal incontinence (leakage of stool)

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