Chronic constipation

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Contents

Introduction

Constipation is one of the most common presenting symptoms. Chronic constipation occurs when symptoms persist for more than 6 weeks. These symptoms may be (a) less than 3 bowel movements a week, (b) straining during defecation for more than 25% of the time or (c) frequent inability to evacuate the rectum completely. Chronic constipation by itself is not a life-threatening disorder; although dangerous disorders such as colorectal cancer should be excluded by colonoscopy as appropriate. It should only be treated if it causes complications which interfere significantly with quality of life. Such complicatons include abdominal distension, stercoral ulcers and anorectal problems. It should be remembered that chronic constipation is a symptom and not a disease. Management involves diagnosing the underlying cause and treating it. An understanding of colorectal motility physiology is required for this.

Physiology and physiologic testing

A solid meal passes from the mouth to enter the caecum in 4 hours. Residue in this meal reaches the rectosigmoid by 24 hours. Colonic motility causes the bowel contents to be retained and mixed, to facilitate absorption; it takes 3–4 days for the meal residue to be finally evacuated in the stools. The frequency of bowel movement in most normal humans ranges from 3 per week to 3 per day. About 70% of stool consistency is water, and inadequate water intake may result in harder stools that are difficult to evacuate.

The motility of the colon has 3 patterns: (a) retrograde peristalsis, which occurs mainly in the right colon (b) segmentation, which results in minimal transit over the colon and occurs mainly in the left colon and (c) mass movement, which results in propelling contents over long distances but occurs only a few times daily. Motility is likely controlled by a pacemaker in the transverse colon, which also acts as the main region of storage. Colonic motility is under enteric nervous and endocrine control. It can be significantly affected by physical activity, dietary fibre and emotional states. The transit which results from colonic motility can be assessed by imaging studies. Transit marker studies involve ingesting non-absorbed radio-opaque markers. Colonic transit is estimated by taking plain X-rays after standardized time intervals. The proportion and distribution of any retained markers are then assessed. Alternatively, some hospitals are using radio-isotope scintigraphy techniques.

Aetiology of constipation

The causes of chronic constipation can be worked out from an understanding of the physiology. A classification of the more common causes is given in Aetiology of constipation

Evaluation of the patient with chronic constipation

The evaluation of chronic constipation can be worked out from an understanding of the more common causes (see Diagnostic algorithm for chronic constipation.).

Diagnostic algorithm for chronic constipation.

History

A detailed medical and dietary history must be taken of the patient history as well as bowel habit. First, it must be ascertained that the severity and chronicity of the symptoms described qualifies to be evaluated as chronic intractible constipation. Sporadic episodes of acute constipation respond readily to laxatives and do not justify subjecting the patient to extensive investigations. In addition, chronic constipation must be differentiated from recent change in bowel habits, especially with rectal bleeding. Obviously, a colonic neoplasm must be exluded in the latter case. In chronic constipation there is unhindered passage of flatus, but in colonic obstruction there is obstipation. However, chronic constipation with faecal impaction can cause intestinal obstruction, but this is usually only in the elderly nursing home or spinal cord injury patients. Sometimes, chronic constipation with faecal impaction can present paradoxically as overflow diarrhoea or faecal incontinence.

Second, the impact of the symptoms upon the patient's quality of life should be assessed by the amount of laxatives needed, complications of chronic constipation and interference with the patient's happiness. Sometimes patients may even need anal or vaginal digitation to help evacuate the stool. Third, appropriate associated questions related to the common causes may clinch the diagnosis.

Physical examination

Although the physical examination will concentrate on the abdomen and anorectum, careful systemic examination is important to exclude systemic causes of constipation (Aetiology of constipation). Physical examination in patients with chronic constipation is usually unremarkable or may reveal abdominal distension with a colon full of faeces.

Diagnostic investigations

A colonoscopy or double-contrast barium enema is very often needed to exclude dangerous organic pathology such as neoplasm. In chronic constipation, a barium enema is preferable because the colon can be dilated and tortuous, especially with megacolon. This would make colonoscopic intubation difficult. The tests commonly used to help identify surgically treatable causes of constipation are transit marker studies, anorectal manometry and defecating proctogram. Their nature (see ‘Physiology and Physiologic Testing’) and application (see Diagnostic algorithm for chronic constipation.) have already been described above. In some specialist colorectal units, personality testing is also used in assessing the patient for surgery because chronic constipation is commonly associated with pschological problems.

Management

Management is directed towards the primary cause of the constipation (see Aetiology of constipation). The student is referred to standard textbooks of internal medicine for the management of the various systemic causes of constipation. When the primary pathology does not lend itself to treatment or when no pathology is identifed, management is symptomatic. This consists of dietary advice, improving bowel habits, encouraging exercise and the use of laxatives, enemas or suppositories. At least 30 g of dietary fibre together with sufficient fluids are needed to have an adequately bulky but soft stool each day. Other simple measures like developing regular bowel habits and not ignoring the need to pass stool may be all that is required to correct simple constipation. Regular exercise also improves bowel function. Faecal impaction should be digitally cleared to enable the other measures to work properly. A classification of the commonly used laxatives is given in Laxatives. No evidence is available as to which laxative or laxative regime is superior.

Management of specific conditions associated with constipation

Irritable bowel syndrome

Irritable bowel syndrome is the most common gastrointestinal disease, occuring in 15% of adults in Western societies. It is a characterized by altered bowel habits, abdominal pain and absence of detectable organic pathology. Diagnosis includes a history of at least 3 months and there are 3 types of clinical presentation: (a) abdominal pain and constipation, (b) alternating constipation and diarrhoea, or (c) chronic painless diarrhoea.

The majority of patients with milder symptoms will be satisfied with the reassurance that dangerous diseases like colorectal cancer have been excluded for example by colonoscopy. Those more severely affected may require counselling to avoid stress or precipitating factors, dietary advice, drugs for symptomatic relief of pain and bowel frequency problems, and rarely formal psychological management.

Slow-transit constipation (colonic inertia)

Slow-transit constipation is likely a disorder of colonic innervation, but this is still poorly understood.Women in the second or third decades of life are most commonly affected. Transit marker studies typically show retention of more that 20% markers 5 days after ingestion, in a diffuse pattern. Total colectomy with ileorectal anastomosis is recommended for intractible cases.

Puborectalis paradox (anismus)

The puborectalis and anal sphincters normally relax during defecation, to allow the passage of stool. Puborectalis paradoxus occurs with inadequate relaxation, resulting in pelvic outlet obstruction. It is possible that a rectal motility problem also exists. The diagnosis is made at anorectal manometry and defecating proctography. Recommended treatment is anorectal biofeedback, to supposedly re-train the puborectalis muscle to relax properly during rectal evacuation.

Rectocele

Rectocele is a weakness of the anterior rectal wall, the rectovaginal septum and the posterior vaginal wall. At defecation, the weakness allows faeces to be diverted into a pouch in the vagina. Patients often have to reduce this pouch with a finger, in order to initiate defecation. Where a rectocele specifically causes constipation symptoms, surgical management is best directed at the rectal side where there is a high pressure zone. A transanal rectocele repair is recommended.

Other causes

The specific conditions like rectal intussusception, sigmoidocele, Hirchsprung's disease (especially shortsegment disease in adults) and Chaga's disease are relatively rare. The interested student is directed to standard textbooks on colorectal surgery.

Further reading

Lembo A, Camilleri M. Current concepts; chronic constipation. N Eng J Med. 2003;349:1360-1368.

Tjandra JJ, Ooi BS, Tang CL, Dwyer P, Carey U. Transanal repair of rectocele corrects obstructed defecation if it is not associated with anismus. Dis Colon Rectum. 1999;42:1544–1550.
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