Introduction

Constipation is a symptom and not a condition.
It is most common in women and the elderly. Often it is more like a perception that a real entity.
It can be affected by psychological factors. For example, it is possible to override the body’s autonomic responses subconsciously and thus exert a higher form of control over them and change the body’s reaction to certain situations. This is more common in women than men, and can often have a social aspect; e.g. women are embarrassed to go for a poo at work, or whilst out of the house. Some people argue that it is because we are conditioned from childhood that pooing is something dirty that we do in private and no-one else has to know about it. This may happen in constipation, but the process can be reversed if people ‘learn’ how to let their natural responses take over.
  • Constipation patients can be given ‘lessons’ on how to poo. At first many patients are wary of this technique and sceptical. It may take several lessons before they relax and settle down and understand what it is for, but it is possible to ‘learn’ how to poo normally again.
Constipation is defined clinically as a ‘change’ from your normal bowel habit. Normal can be anywhere from 3 times a day to 1-2 times a week. The important this is what is normal for you. When constipation is present there will usually be some degree of straining, perhaps a feeling of incomplete evacuation and lumpy or hard stools.

What causes constipation

There are many, many causes, important ones include:
  • Lack of fibre & fluid intake
  • Lack of physical activity
  • Irritable bowel syndrome
  • Drugs – particularly opiates, but also iron supplements, anti cholinergics, calcium antagonists and aluminium containing ant-acids.
  • Neurological causes – e.g. MS, parkinson’s, a CVA, spinal chord lesions
  • Metabolic causes – pregnancy, diabetes, hypercalcaemia, hypothyroidism
  • Depression – possibly linked to general decreased activity of the nervous system and less 5-HT.
  • Hirschprung’s disease
  • Colonic carcinoma
  • Diverticular disease
  • Obstruction
  • Crohn’s
  • Fissures
  • Haemorrhoids
  • Pregnancy – it has been shown that progesterone reduces colonic muscle tone, thus leading to constipation. This also sometimes has an effect during a woman’s menstrual cycle – if a woman is constipated, the symptoms may be worse during the luteal phase of her cycle.
  • Diabetes, hyperthyroisim and hypercalcaemia can all lead to altered motility.

Pathology

The role of the colon is to absorb water and electrolytes, and move faeces along to the rectum. About 2L of fluid pass into the large bowel each day. Stimulation of peristalsis is mostly by short chain fatty acids which are produced by the break down dietary fibre by floral bacteria in the ascending colon. It is also stimulated by release of serotonin (5-HT) by local neurones in response to colonic distension.
Normal colonic transit time is 8-24 hours, with on average 250g of stool production each day.

Types on constipation

Constipation can be broadly divided into 3 categories:
  • Normal transit constipation (59%) – in this type of constipation, stools travel through the colon at the normal rate. Patients also have normal stool frequency, but they believe they are constipated – this is probably because they have difficulty with the act of actually passing a stool. Patients often claim abdominal pain and bloating.
    • This condition can be assessed by ingestion of radio markers – various shapes that are ingested on different days to identify how long it takes a shape to travel through the colon. This type of test helps distinguish slow transit from normal transit constipation
  • Slow transit constipation (13%) – this often occurs in young women, and will result in defecation of less than once a week. The condition often starts at puberty and symptoms involves abdominal pain, bloating, and infrequent urge to defecate. The diagnosis can be difficult as it is similar to that of constipation due to IBS. Some patients with this condition have impaired bowel emptying, and some have impaired stimulation of colonic motility. Some patents will also have co-existing disorders of the small intestine that may be consistent with a diagnosis of chronic idiopathic pseudo-obstruction.
  • Defacatory disorders (25%)- this is often caused by improper relaxation of the puborectalis muscle, external anal sphincter and other associated muscles of defecation. It is a bit of a paradox, because through straining too hard, people can prevent these muscles from relaxing. It is especially common in women and may actually be a learned response. Often an anterior rectocele may form. This is where there is a weakness in the rectal/vaginal septum, and a protuberance of the rectum may form If this protuberance has a diameter of >3cm, then faeces can get stuck in it. In other patients, the mucosa of the anterior wall of the rectum prolapses downwards during straining, preventing proper emptying of the rectum. In some patients, the rectum may become overly sensitive to the presence of small volumes of faces in the rectum, and as a result the patient will pass small volume stools frequently, and often have a sensation of incomplete evacuation.
    • Defecation disorders can be diagnosed by using imaging of the rectum during defecation.

Investigations

  • You may want to perform a vaginal and rectal examination if you suspect that the constipation is caused by a pelvic floor defect (can happen in childbirth, trauma or in serious colonic disease). An easy way to rule this out is to see if the perineum descends on straining. If it does not, then it is a pelvic floor dysfunction.
  • Radio opaque markers (as seen above)
Examination is perhaps more important than investigation. Some important things to look out for are:
  • Check the perineum and do a PR. You might find impaired sensation or disorders of the rectal floor. You may also feel a rectal mass, or a prolapse, and it is very important when you do a PR that you ask the patient to squeeze your finger to test anal sphincter function.
Here we can see various radio-opaque shapes ingested on 3 separate days. The imaging is always done 120 hours after ingestion of the first set of shapes, and thus from this we can see that all the shapes are still present, and are spread along the colon, thus confirming a diagnosis of severe slow transit constipation.

Treatment

It is very important that the underlying condition is treated as the main priority. Education is also an important factor – patients should be educated on patterns of normal bowel movement, and reassured, that even 1-2 times a week is normal for some people. Those who are obese and lead a sedentary lifestyle should be encouraged to lose weight.
Most people will respond to increased dietary fibre and fluid intake, and if necessary, laxatives. You don’t need to PR every patient! This is more likely after first line treatments have failed, or in especially risky patients – i.e. they have a short history and also experience rectal bleeding – and as such you are very suspicious of rectal carcinoma. – in such cases you should always refer the patient for a barium enema and / or colonoscopy.
It is extremely important not to become reliant on laxatives. They can permanently alter the functioning of the bowel.
  • Normal and slow transit constipation – the first line treatment of this should be an increase of fibre and fluid intake in the diet. You should try to increase fibre through dietary means rather than with fibre supplements – as the supplements can affect the way floral bacteria operate thus not producing the desired effect. Patients should be encouraged to drink 6-8 glasses of water daily, and to eat 20-30g of fibre every day. This approach does not help in all cases.
  • Laxatives –use of these should be restricted to very severe cases. There are different types that act in different ways
    • Osmotic laxatives –these draw fluid out of the interstitia and into the colonic lumen. A common example is magnesium sulphate (5-10g), taken usually at breakfast time, it will work within 2-4 hours.
    • Stimulatory laxatives –these work by stimulating the colonic mucosa to contract more often, thus, churning up the stool and moving it along the bowel quicker. Some may also increase intestinal secretion.
    • Enema –this may be performed in the elderly and infirm, and those with neurological disorders.

 

For more information, see the article Altered Bowel Habit

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