11 Constipation
Case
A 33-year-old female accountant consults because of worsening constipation. She describes on specific questioning passing a bowel movement every 2 days. She strains excessively to pass the bowel movement, and the stools feel hard. She has a sensation of incomplete emptying after she has a bowel movement, and she finds this troubling. Occasionally, she will press around the anal area to help hard stool evacuate. She remembers being constipated as a child and all her life. She has not seen any mucus or blood in the stools, and she has no history of weight loss, vomiting or any alarm symptoms. She describes mild abdominal discomfort at times; this is usually present before she passes stools, but she denies pain relief with defecation or a change in her stools when pain begins. She has been regulating her bowels by taking over-the-counter laxatives, but has found that these have not been very helpful. She never has diarrhoeal symptoms.
Introduction
Constipation is often dismissed as a minor symptom by doctors, although for some patients it can be the source of considerable anxiety and disability, and is frequently associated with general malaise and a sense of poor health. A list of the causes of chronic constipation is presented in Box 11.1. While the majority of patients who complain of constipation have a benign disorder of colorectal function associated with faulty diet, drugs or bowel habit, called simple constipation, it should always be remembered that constipation may be the presenting symptom of a serious colonic disorder, such as carcinoma, or a generalised metabolic disorder, such as hypothyroidism or hypercalcaemia. Chronic constipation can occur in the absence of structural or metabolic disorders because of abnormally slow colonic transit (slow transit constipation), obstructed defecation (pelvic floor dysfunction), or both. The irritable bowel syndrome, characterised by abdominal pain and a variable bowel habit, is also an important cause of constipation (Ch 7). A careful history and examination to ascertain the likely mechanism producing constipation allows investigations to be correctly chosen, which in turn should determine management.
Clinical Approach to Patients with Constipation
History
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.
Physical examination
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.
Investigations
Generally, types of constipation can be divided into those with no apparent structural abnormality of the anus, rectum or colon and those with recognised structural disease such as cancer, a stricture or megacolon. A third group of patients have generalised metabolic, neurological or endocrine diseases, which may produce constipation as a secondary event (Box 11.1).
The extent of investigations for the individual patient with constipation depends very much on the clinical assessment (Fig 11.1). In young patients in whom suspicion of serious underlying disease such as colon cancer is low, a trial of therapy without investigation is reasonable. In most other patients it is logical to first assess that the colon is structurally normal. In those patients who do not respond to initial simple therapy, further investigations may be necessary.
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.
Radiology
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.
