constipation

constipation is a widely used term usually referring to decreased bowel frequency, although it is sometimes used when the stools are hard or when there is pain or difficulty with bowel evacuation. A clear definition of the term is difficult because of the wide range of ‘normal’ bowel frequency in the general population, which ranges from two or three times a day to less than two per week. Constipation has many causes, the majority of which are not serious and for which there are simple remedies. However, as it may be the presenting feature of a serious condition such as large bowel cancer, in selected circumstances constipation requires further investigation to enable specific treatment to be given. There are a number of important groups of disorders which present as constipation.

Causes of constipation

When the structure of the bowel is apparently normal

Most individuals fall into this group, and the most common cause is usually dietary. Low fibre diets result in low faecal residues, which can reduce the frequency of bowel action. In some individuals constipation may be a behavioural problem, possibly related to a life-long suppression of the normal ‘signals’ to defecate. Other situations like pregnancy and old age and infirmity also slow intestinal transit and can result in constipation. Some patients with irritable bowel syndrome complain of constipation which may alternate with increased bowel frequency.

Structural abnormalities in the colon and rectum

Minor anal problems such as ‘anal fissure’ — a tear in the lining of the anal canal — can result in constipation because of voluntary inhibition of defecation due to the associated pain. Inflammation in the rectum, proctitis, can have the same effect. In addition, there are some important disorders in which there is a developmental or acquired abnormality of the nerves within the bowel wall; examples include Hirschsprung's disease (congenital ‘megacolon’ described by this Danish physician in 1888) and infection with the parasite Trypanosoma cruzi, which causes Chagas' disease (named after the Brazilian physician who noted it in 1909). Abnormalities of colonic muscle produce a myopathy which can also lead to constipation.

Neurological diseases

A number of generalized neurological disorders, such as Parkinson's disease and multiple sclerosis, can damage the nerve supply to the colon and rectum and produce constipation. Similar damage to the autonomic nerves can also occur in diabetes mellitus. Colonic function may also be impaired in patients with reduced levels of consciousness and mental retardation.

Endocrine and metabolic

causes Reduced activity of the thyroid gland (hypothyroidism) and raised concentrations of calcium in the blood (hypercalcaemia) are the most common disorders in this group.

Psychological disorders

Depression and anorexia nervosa are both often associated with constipation.

Adverse drug effects

Many drugs can cause constipation, in particular potent painkillers (opiates and opioid analgesics), some anti-depressants, and drugs used to reduce high blood pressure.

Investigation and management of constipation

Investigation of constipation which has no simple explanation may require exclusion of a structural problem in the colon; this usually involves a radiological examination (barium enema) or an endoscopic examination using a flexible instrument called a colonoscope. Nerve and muscle disorders sometimes require investigation using methods to measure transit time through the colon, and measurement of pressure within the bowel and electrophysiological tests to study nerve and muscle function.

Simple constipation, in which there is no obvious disease or disorder of the colon, is best remedied by dietary measures such as increasing the fibre content of the diet. Commercially-prepared bulking agents are also available. If bulking agents fail then osmotic laxatives such as magnesium sulphate (Epsom salts) may be required, though there is some evidence that prolonged use can damage the colonic nerves and ultimately make the condition worse.

When constipation is due to colon cancer or an endocrine or metabolic disturbance, then appropriate specific treatment is required. If constipation occurs as an adverse effect of drug therapy for another condition, then it is usually appropriate to try an alternative preparation.

Michael Farthing, and Anne Ballinger

See also alimentary system; defecation; toilet practices.