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Disordered Defaecation

Disordered defaecation is a descriptive term for a number of problems which can affect the mechanisms influencing the passage of stools from the large bowel into the outside world (usually the toilet!). The normal control of the passage of wind and stool relies on some pretty amazing mechanics. Firstly the rectum (the last part of the bowel fills with stool and the vault (roof of the rectum relaxes to a point. At a given distension messages will go from the rectal nerves to the brain to let you know you need to open the bowel. At this stage the anal sphincters (and there are two sets – internal and external remain contracted, once you ar ready to defaecate these sphincters relax, but in addition the pubo-rectalis mucle, one of the levator ani or pelvis floor muscles, which acts as a “sling” preventing more stool entering the rectum will also relax. The rectal pressure will increase as peristalisis shortens the rectum and push stool into the anal canal. The anal sphincters should relax allowing the stool to pass into the outside world. All this requires the delicate integration of autonomic, enteric and voluntary nervous systems.

Sometimes this complex co-ordination can go wrong. The puborectalis muscles may fail to relax causing the failure of stool to drop into the rectum leading to a small stool and a sensation of incomplete emptying with the urge to defaecate returning soon after the initial act. Similarly the anal sphincters, which should normally relax may fail to do so causing a failure of the normal anal canal to open and allow stools to pass. This failure of either the pubo-rectalis or the rectal sphincters to allow the formation of a proper channel is known as anismus (a latin word meaning without an opening/channel. Some patients may find part of the rectal wall falls (prolapses) over the opening of the anal canal causing obstruction of the anal canal this is known as obstructive defaecation.

Whilst for some the problem is being unable to defaecate properly for other the issue is a failure of function in the anal sphincters, either due to a neurological problem or due to trauma. The commonest cause of trauma is childbirth, where rarely extensive vaginal tears can lead to tearing of part of the anal canal. If the sphincters do not function properly this can lead to incontinence.

 Treatment of disordered defaecation depends on the cause. For many patients with anismus biofeedback or “re-education of the bowel” is often helpful in restoring the normal mechanism of defaecation. For those with obstructive defaecation biofeedback or surgical intervention may be indicated, however surgery should not be undertaken lightly and she only be considered following thorough evaluation in expert hands.

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