Anyone can become constipated at some point in their life, typically in association with a change in diet, a long period of travel, or pregnancy. In some people, constipation results from habitually ignoring the urge to have a bowel movement. In the vast majority of people, a healthy diet, plenty of fluids, and exercise is all that is needed to prevent constipation. Eating foods high in fibre, including breakfast cereals, wholegrain bread, and fresh fruit and vegetables should provide the 25–30 g of fibre needed for healthy bowel function, although population studies show that many people do not have this level of fibre intake. Drinking 6–8 glasses of water a day and getting regular exercise also help to maintain a healthy colon.
Daily bowel movements are generally considered to be ideal, but there is great variation around this. Passing stool anywhere between three times daily and three times weekly is still within normal limits.
Unfortunately, there is a significant number of people who suffer from chronic (ongoing) constipation. Medically this has a very complex definition, and in fact this definition is only useful for research. In everyday life, chronic constipation can mean different things to different people. Often it refers to infrequent bowel movements, but it can also refer to hard stool, straining to pass stool, and a sense of incomplete emptying, along with a need to take laxatives or suppositories to keep regular. That said, patients with chronic constipation visiting my colorectal clinic are more likely to complain of abdominal bloating, passing wind, and abdominal pain than infrequent bowel movements. Depending on who you ask, anywhere between 2% and 30% of people are thought to suffer from chronic constipation, but the overall accepted figure is around 10%–12%.
Chronic constipation can be classified as functional (primary, a condition in its own right) or secondary (resulting from an underlying condition). Functional constipation can be broadly divided into three classes, ie, normal-transit, slow-transit, and outlet constipation.
Functional chronic constipation
In people with normal-transit constipation, the way muscles contract and relax to move contents through the colon (colonic motility) is not altered, and stool passes through the colon at a normal rate. These people may complain of infrequent bowel movements, but have normal colonic transit tests. However, patients with this type of chronic constipation may have trouble emptying their bowels for another reason, eg, harder stools, which are more difficult to pass. As with other patients with chronic constipation, it is the bloating and abdominal pain that are the most troubling problems for the patient and where therapy is directed.
Patients with constipation-predominant irritable bowel syndrome (IBS-C) fall into this group. Some patients with IBS and diarrhoea alternating with constipation (IBS-A) are believed to have altered gut bacteria in the small bowel. When methane-producing bacteria are in predominance, the patient becomes constipated, and when there are changes to hydrogen-producing bacteria, the patient develops diarrhoea. In IBS-C, again there are many different ways of producing the constipation, but it may be that the makeup of the bacteria in the gut affects its motility.
In a person with a normally functioning bowel, the large intestine massages waste along its length to the rectum by rhythmic, muscular contractions of its walls (peristalsis). This activity is controlled by nerves of the enteric nervous system (ENS). In patients with slow-transit constipation, the time taken for stool to pass through the colon is decreased and bowel movements are less frequent, leading to symptoms like straining and harder stools. This disorder is thought to be caused by abnormal functioning of the ENS. Certain primary bowel motility problems may have constipation as their main symptom. Some patients are born with a peristalsis problem while others are born with a normal bowel, but events in their life change the way bowel works, so they develop a similar inability to move bowel contents along towards the rectum. The unusually slow passage of waste through the large intestine leads to chronic constipation. There are multiple forms of medical therapy available and most people with slow transit constipation will never need surgery. It is possible to perform surgery in some patients with slow-transit constipation, but this is only done after extensive investigation, which needs to examine the transit ability of the rest of the bowel. This surgery takes the form of a sub-colectomy, which is not straightforward or able to be reversed, and complications can occur.
Persons with outlet constipation often have pelvic floor dysfunction, ie, a defect in the coordination necessary for evacuation of stool. This usually occurs because of failure of the pelvic floor muscles (including the anal sphincter) to relax appropriately when going to the toilet. When this happens, stool passage is much more difficult, regardless of whether stool transit in the colon is normal or delayed. Obstruction to defaecation can also occur at the anorectum and this can be due to weakness of the pelvic floor and wall of the rectum, resulting in the rectum collapsing on itself (internal rectal prolapse) or ballooning out of the anus (rectocoele, external rectal prolapse).
Secondary chronic constipation
Many medications can slow the movement of food through the colon and worsen constipation. These agents include opioid-based pain killers, diuretics, antiepileptic drugs, antispasmodics, antidepressants, tranquilisers and certain other psychiatric medications, antihistamines, blood pressure medication, calcium channel blockers, iron or calcium supplements, and aluminium-containing antacids.
An underlying condition
Certain medical conditions can also lead to chronic constipation. These conditions include severe hyperthyroidism, hypercalcaemia, diabetes, coeliac disease, and certain neurological disorders such as Parkinson’s disease and myotonic dystrophy. Any problem at the end of the gastrointestinal tract that limits the ability to pass stool can also cause constipation. People may develop chronic constipation if they have an anorectal problem such as a painful anal fissure, where the patient may avoid going to the toilet, anismus, where the anal muscles contract instead of relaxing when the patient is trying to pass stool, and pelvic floor prolapse, where a prolapse of the rectum may cause the patient to have the sensation of blockage. Anal fissure and anismus can be treated by Botulinum toxin injection. Pelvic floor prolapse can be treated by pelvic floor physiotherapy, laxatives and occasionally surgery.
Seek a medical specialist’s opinion
People with a normal healthy colon can improve their bowel function by increasing their fibre intake, drinking plenty of water. However, these measures may not work people with IBS-C or IBS-A, and indeed may make their symptoms worse. The same is true for people with slow-transit constipation.
Chronic constipation is not thought to lead to anything serious, such as cancer. However, long-term dilatation of the bowel can lead to nerve damage and worsening of constipation because of reduced motility of the large bowel. In addition, chronic straining may lead to muscle and nerve problems in the pelvic floor.
Any change in bowel frequency or stool consistency should be reported to a doctor. More serious causes of constipation need to be excluded before a diagnosis of constipation is made. These include narrowings in the colon caused by repeated attacks of inflammation from diverticular disease or cancer of the colon. Any persistent change in bowel habit, increase or decrease in frequency or size of stool, or increased problems passing stool warrants an appointment with your family doctor. You should also be referred to a colorectal surgeon, who will organise a colonoscopy if this has not been already.
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