History

First, the history should be taken. If the problem is a chronic one, ask why the patient has sought help on this occasion. He or she may have fears about the possibility of malignancy or the chronic use of laxative drugs. Details of bowel frequency, stool consistency and colour, presence of blood or mucus and accompanying features such as abdominal pain, bloating or weight loss are therefore relevant. Stools that feel hard to the patient usually are not when objectively tested!

The onset of the complaint should be ascertained. Constipation dating from the neonatal period may suggest Hirschsprung’s disease (congenital aganglionosis causing absent peristalsis in a part of the rectum or colon), whereas symptoms dating from the time of toilet training or early childhood may suggest childhood megarectum or stool withholding (often with soiling and overflow). Severe constipation (with a defecation frequency of less than once a week off laxatives) in young women dating from adolescence or following pelvic surgery may indicate colonic inertia (slow transit constipation); these patients typically lack the urge to defecate. In older patients, progressive constipation may indicate a colorectal neoplasm or diverticular stricture.

Some patients with a disorder of pelvic floor function complain of a sense of difficulty with evacuation and feeling of anal blockage or obstruction; they may manually disimpact themselves by pressing in or around the rectum or vagina. A history of obstetric trauma in such patients may be relevant. However, symptoms cannot distinguish pelvic floor dysfunction with sufficient accuracy from irritable bowel syndrome or functional constipation.

Constipation may be induced by certain drugs, such as narcotics, antihypertensives or antidepressants. Thus, it is very important to ask about the use of drugs and whether their introduction corresponded to recent alterations in bowel habit. A lack of dietary fibre is a common cause of constipation and a full dietary history should be taken. Slow transit constipation, and occasionally simple constipation, may run in families and a history of other family members being similarly affected may provide useful information.

If the problem is chronic, it is important to find out whether previous investigations have been performed and what previous treatment regimes have been employed, including alternative medicine treatments.

Physical examination

An important part of the assessment of patients with chronic constipation is the physical examination. The general demeanour of the patient may give information regarding anxiety or depression. Signs of neurological or endocrine diseases, such as hypothyroidism or Parkinson’s disease, should be looked for. Abdominal palpation may reveal faecal masses in young patients with rectal impaction or a tender spastic colon in a young anxious patient with irritable bowel syndrome. A craggy abdominal mass may indicate a colonic neoplasm.

A rectal examination is important. The perineum should be inspected for painful anal fissures, fistulae, abscesses or local neoplasm. The patient should be asked to bear down to demonstrate perineal descent due to pelvic floor weakness, haemorrhoidal prolapse or the formation in women of a rectocoele or uterine prolapse. Occasionally, rectal mucosal or full-thickness prolapse may be seen (Ch 22). An anal fissure will be very painful on trying to put your finger in the anal canal. Obvious fistula suggests Crohn’s disease. A rectal examination can detect if there is any evidence of anal canal stenosis. An obvious rectal mass may represent a cancer. Obvious faecal impaction may be present in very severe constipation, particularly in the elderly. To complete the rectal examination, the patient should be asked to try to push the examiner’s finger out by straining. If the puborectalis and anal sphincter contract and increase pressure in the anal canal rather than relaxing to widen the canal, this suggests (but is not diagnostic of) pelvic outlet obstruction. Next, turn your finger to the anterior position. Try to feel if there is any evidence of a rectocoele, which pushes through the anterior rectal wall when straining. Sigmoidoscopy should be performed if adequate rectal emptying can be achieved.

Haematology and biochemistry

It is reasonable to check for anaemia (especially iron deficiency) and a raised erythrocyte sedimentation rate or C-reactive protein result. Biochemical tests to check thyroid function and serum calcium levels may also be performed.

Colonoscopy

Colonoscopy is the test of choice to exclude significant structural colonic disease. It is an alternative to sigmoidoscopy and barium enema. Melanosis coli may be evident in patients who use laxatives regularly (Fig 11.2). Colonic stricture and neoplasm can usually be effectively diagnosed by this technique.

Figure 11.2 Melanosis coli.

Radiology

A plain abdominal x-ray examination often gives useful information about colonic loading and the presence of distended loops or fluid levels if obstruction is a possibility. The plain x-ray examination is also often helpful in children in whom megarectum is suspected. The rectum or colon is of increased diameter in adult patients with megacolon (due to Hirschsprung’s disease or chronic idiopathic intestinal pseudo-obstruction).

An unprepared barium enema is useful to assess the size, shape and configuration of the distal colon, especially in cases where rectal impaction or Hirschsprung’s disease is suspected. A double-contrast barium enema after bowel preparation can assess a structural disorder, such as stricture, volvulus or megacolon.

Virtual colonoscopy (CT colonoscopy) is a radiological technique that provides a three-dimensional reconstruction of the colon; it can accurately detect large colonic polyps (1 cm and over) or cancer. A bowel preparation is required. Extra colonic findings are seen commonly; one in 10 is sent for additional testing but this is of little benefit in the majority.

Colonic transit studies

Firmer stool consistency is correlated with slower colonic transit. Total gut transit time (to which the colonic transit time is the greatest contributor) may be simply measured by giving radio-opaque shapes by mouth and recording their course through the colon by abdominal x-ray or stool collection. It is known that normal subjects pass 80% of administered shapes by 5 days.

One clinically useful quantitative test is to give 24 radio-opaque markers by mouth on 3 consecutive days and obtain a plain abdominal x-ray examination on day 4; the number of markers is counted to calculate total and regional colonic transit times (Fig 11.3A and B). A transit time of 70 hours or longer is abnormally slow. Laxatives should be stopped 2 days prior to the test and a high-fibre diet should be continued throughout. Patients should be off opioid painkillers.

Figure 11.3 A Normal colonic transit. B Slow colonic transit (over 70 hours).

More sophisticated techniques involve radioisotope labelling of food material, such as bran, to allow isotope scanning to measure colonic clearance. This can provide information regarding specific emptying times for different segments of the colon.

Ano-rectal manometry, sensation and balloon expulsion

Pressure within the anal canal may be recorded by perfused tubes, microballoons, or strain-gauge transducers (see Ch 16). Resting anal tone and the response to voluntary contraction and straining at defecation give useful information about the state of the pelvic floor muscles.

The recto-sphincteric reflex may be elicited by rectal distension with simultaneous recording of anal pressure. A positive reflex consists of a relaxation of the internal anal sphincter (lowered resting anal tone) following rectal distension (Fig 11.4). The reflex is mediated by the myenteric plexus and is characteristically absent in those with Hirschsprung’s disease (because of congenital aganglionosis).

Figure 11.4 To elicit the rectoanal reflex, a balloon is inserted into the rectum and a pressure measuring device (in this case a microballoon connected to a pressure transducer and chart recorder) is placed in the anal canal. Distension of the balloon causes an initial rise in pressure, due to the external anal sphincter contraction, followed by a more prolonged fall in anal pressure due to internal anal sphincter relaxation. This latter fall in pressure confirms the presence of intact intramural nerves, excluding Hirschsprung’s disease. A false negative result is sometimes seen in patients with an idiopathic megarectum.

From Kamm MA, Lennard-Jones JE, eds. Constipation. Petersfield: Wrightson Biomedical Publishing; 1994, with permission.

Rectal sensation can be tested by inflating a rectal balloon with increments of air, noting the onset of initial sensation and the maximum tolerated volume. Using more sophisticated equipment, a pressure volume curve may be obtained. These tests are useful in distinguishing the hypertonic rectum of the irritable bowel syndrome from the large, insensitive rectum of megacolon.

Assessment for pelvic outlet obstruction may be made with a very simple screening test: the expulsion of a 50 mL filled balloon. If the patient is unable to expel the balloon within 1 minute, this strongly suggests there is pelvic floor dysfunction (outlet obstruction). In some laboratories, additional weights are added to the balloon and patients are still unable to expel it even with 500g or more of weight on the balloon—further evidence of outlet obstruction. Paradoxical contraction of the external anal sphincter on straining (when it should normally relax to allow stool passage) supports a diagnosis of pelvic outlet destruction.

Dynamic proctography

Video radiographic recording of defecation with contrast material in the rectum (by a defecating proctogram or magnetic resonance imaging) will demonstrate perineal descent, rectal intussusception and paradoxical sphincter contraction in some patients with obstructed defecation (Ch 16).

Motility studies

Small bowel motility can be measured by placing a manometric assembly through the mouth in the upper small intestine. Chronic intestinal pseudo-obstruction, a rare but important cause of slow transit constipation, can be diagnosed by this test (Ch 7). Recording of colonic motility is a research tool and is not routinely used to base diagnosis and management.

Rectal biopsy

In rare cases where the history, x-ray findings and results of physiological studies suggest the possibility of Hirschsprung’s disease, a rectal biopsy is usually necessary for confirmation. Traditionally, this has been of the full-thickness type, requiring general anaesthesia. More recently, suction biopsies with special stains have been shown to be useful, especially in children.

General measures

In general terms, many patients with constipation may be managed by a high-fibre diet containing 20–30 g of fibre. This can be achieved by adding cereal, unprocessed bran, and fruit and vegetables (especially root vegetables and legumes) in conjunction with an increased fluid intake. Bulk-forming agents are useful supplements. There are two types: those derived from ispaghula, sterculia (a plant gum) or methylcellulose. Instructions should be given on regular toilet habit and exercise. A review of intercurrent drug therapy should be undertaken and, if possible, drugs promoting constipation should be stopped.

Therapeutic agents

Therapeutic agents available for the treatment of constipation are listed in Table 11.1.

Table 11.1 Thrapeutic agents in constipation and major side effects

Biofeedback

This technique has been used in patients with chronic constipation due to pelvic floor dysfunction on the basis of failure of rectal evacuation. Those who appear to have a paradoxically contracting anal sphincter during evacuation may be retrained to relax the sphincter during defecation straining to allow easy rectal evacuation, with a 70% success rate. This approach is superior to standard care, and should be considered if laxatives and per rectum evacuants have failed.

Colectomy

Surgical therapy should be regarded as a measure of last resort in patients with very severe constipation and documented slow colonic transit without other disease. The surgical procedure of choice in slow transit constipation is subtotal colectomy with ileorectal anastomosis. Extensive resection is required as lesser resection is usually associated with recurrence of constipation. The procedure should be done only in centres of excellence.

While the majority of patients have increased bowel frequency after ileorectal anastomosis, some have persistent symptoms of pain and bloating, and a few develop megaileum after surgery and continued constipation. In those with documented obstructed defecation such as mucosal prolapse, perineal descent or paradoxical contraction of the anal sphincter on straining, difficulty with rectal evacuation may persist postoperatively and occasionally patients complain of diarrhoea and incontinence. Hence, pelvic floor dysfunction and small intestinal dysmotility must be excluded before colectomy is considered. Even so, currently it is still difficult to predict the outcome of surgery based upon preoperative physiological studies.

Other surgical approaches

Other treatment modalities

Botulinum toxin injected into the anal sphincter may help some with paradoxical anal sphincter contraction but is not longlasting.

Much research is being directed towards the complex interaction between the central and enteric nervous symptoms. New drug approaches include use of neuronal growth factors. Electrical stimulation is also being tried. In some patients with chronic constipation, there may be a psychological abnormality and alternative approaches to therapy, such as relaxation and behavioural therapy or hypnotherapy, may have a role to play, although no strong scientific evidence supports their use.

Simple constipation

This may be defined as that caused by faulty diet, bowel habit, travel or drugs. Once organic disease has been satisfactorily excluded, treatment of this group should be along the lines outlined in the general measures above. Dietary manipulation should be used initially and laxative agents only used if the problem does not respond to simple means.

Constipation in elderly people

Approximately 50% of elderly patients in primary care will complain of a disturbance of bowel function, more commonly constipation. Drug treatment given for other conditions often leads to constipation. Other factors include a low fibre intake because of poor nutrition and relative immobility producing difficulties with toilet access.

Many elderly nursing home patients develop rectal impaction and this sometimes produces spurious diarrhoea. This diagnosis can be made by rectal examination. Treatment consists of cleaning out the rectum completely by digital fragmentation, lavage or polyethylene glycol (for 3 days), then prescription of an osmotic laxative, increasing the dose as needed to induce a stool every second day. Occasionally, elderly patients present with obtundation or delirium, which improves as the constipation is treated.

Hospitalised patients

Constipation in hospital is usually multifactorial. If a patient has not passed stool for 2 days, and no clearcut cause is apparent, bisacodyl (10 mg at night) or magnesium hydroxide (in the morning) is reasonable first-line therapy.

Opioid-induced constipation

On initiation of an opiate for pain control, a concomitant laxative regimen is recommended to prevent constipation (e.g. docusate 100 mg orally three times daily and senna 2–8 tablets at night). If constipation occurs despite prophylactic laxatives, obstruction and impaction should be ruled out, then an osmotic laxative (e.g. polyethylene glycol 17 gm) or a bisacodyl suppository (if nauseated) tried. The peripheral opioid antagonist methylnaltrexone does not impair analgesia but does improve constipation in 50% of cases refractory to usual care; it is given by subcutaneous injections twice daily. Low dose oral naloxone is an alternative option.

Idiopathic colonic inertia (slow-transit constipation)

This is a rare disorder mainly seen in young women, and the history usually dates from childhood or adolescence. Typically these patients go for weeks between bowel actions! Occasionally, the problem follows abdominal or pelvic surgery.

It is now recognised that the majority of these patients have loss of the interstitial cells of Cajal, which drive intestinal smooth muscle activity as pacemakers (producing myogenic electrical slow waves). Sometimes this disorder is part of a widespread inherited or acquired defect in intestinal muscle or nerve that causes symptoms of bowel obstruction (chronic idiopathic intestinal pseudo-obstruction). There may be diffuse abnormality of smooth muscle function with abnormalities in oesophageal motility, gastric emptying, small bowel transit and bladder function. Dietary manipulation and other simple measures are ineffective, and usually these patients manage bowel evacuation only with laxatives or enemas.

Other patients may have an abnormality of rectal evacuation producing a hold-up in transit. This could be due to a sensory defect in the rectum as many of these patients appear unable to satisfactorily expel liquid or solid content from the rectum due to paradoxical contraction of the pelvic floor striated muscles during defecation. Pelvic ultrasonography has not demonstrated any significant anatomical abnormality, but many of these women have descending perineum syndrome due to chronic straining at defecation. If pelvic floor dysfunction can be corrected by biofeedback, in true slow-transit constipation, the abnormal colonic function persists.

Medical treatment of this group of patients remains difficult. Osmotic laxatives should be tried in the first instance, but often are unpredictable and are associated with bloating, nausea and frequent loose stools. Occasionally, per-rectal evacuants are useful.

Surgical treatment should be reserved for those with disabling symptoms that have been present for many years when all medical treatment options have been exhausted. In general terms, surgery should be performed only after appropriate physiological and psychological assessment in units with a particular surgical interest in this area. Pelvic floor dysfunction must be corrected if present before surgery is ever considered. Ileorectal anastomosis has been reported to be successful in a small number of patients.

Megacolon

Megacolon is a rare disorder characterised by an increased rectal or colonic diameter on x-ray examination. Hirschsprung’s disease is an important cause. Multiple genetic mutations have been identified in Hirschsprung’s disease, mainly in the RET proto-oncogene. It may present for the first time in adult life and can usually be diagnosed by radiological and physiological tests. An unprepared barium enema will usually show a cone-shaped rectosigmoid transition zone (from narrowed to dilated; the narrowed segment is where there is a lack of colonic ganglion cells). The rectosphincteric reflex on anorectal manometry is absent. Rectal biopsy is needed to confirm the diagnosis. The treatment for Hirschsprung’s disease in adults is surgery.

Chagas’ disease is endemic in tropical South America, particularly Brazil. The disease is caused by the organism Trypanosoma cruzi and causes neuronal damage to cells in the autonomic nervous system, most particularly affecting the hollow organs and heart. Megacolon occurs during the chronic phase of the disease and is associated with a dilated, aperistaltic segment of intestine—often the sigmoid colon. Megacolon and mega-oesophagus often occur together. Patients whose symptoms are uncontrolled by medical measures require surgical resection of the dilated colonic segments.

Those with non-Hirschsprung’s or idiopathic megacolon may be subdivided into patients whose symptoms develop in childhood and patients whose symptoms develop in later life. In the former group, faecal impaction and soiling are usually the presenting symptoms. The initial step is to disimpact the rectum as described above and then maintain the patient on regular oral laxatives. Encouragement regarding regular defecation is important. Sometimes regular per-rectum evacuants are needed to maintain an empty rectum.

Those whose symptoms develop in later life are usually troubled by pain and bloating and respond poorly to laxatives. Many have taken antidepressants, antipsychotics or antiparkinsonian drugs for prolonged periods. Some evidence suggests that these people may have an inherited or acquired defect in nerve or muscle of the colonic wall. Some patients have idiopathic intestinal pseudo-obstruction. If symptoms are severe and unresponsive to medical treatment and the patient is otherwise fit, colectomy usually gives good results.

Endocrine and metabolic causes

Constipation is common in hypothyroidism; megacolon has been reported, and improves if the patient becomes euthyroid on treatment. Hypercalcaemia and acute porphyria can present with constipation and again respond to appropriate therapy.

Autonomic neuropathy

The most common cause is diabetes mellitus. These patients appear to lack the normal gastrocolic response following food ingestion. Prokinetic drugs may be useful in therapy.

Spinal cord lesions

Damage to the sacral cord leads to a distensible atonic distal colon. Constipation is thus a significant problem in paraplegia. Usually, a bowel regimen with a bulk-forming agent, stimulant laxatives and per-rectal evacuants twice or thrice weekly helps to maintain regular bowel patterns.

Other neurological diseases

Constipation may accompany multiple sclerosis, Parkinson’s disease (before other neurological signs develop) and psychosis or dementia. Constipation may be seen in depression or anorexia nervosa. Treatment should be along the usual lines in a stepwise fashion as outlined.