Constipation can be defined as a reduction in the frequency of bowel movements. A normal frequency is considered to be between three times a day and every 3 days, but there is considerable individual variation. Hard, difficult to pass stools are also considered constipation, even if frequent.
Causes include drugs (e.g. opiates), endocrine or metabolic causes (e.g. hypothyroidism, hypercalcaemia, hypokalaemia) and neurological diseases (spinal cord injury, multiple sclerosis). Constipation may also be the presentation of bowel malignancy, which should be suspected in the older person, particularly if there is a family history, history of rectal bleeding or weight loss. Left-sided colonic malignancies frequently present with a triad of alternating constipation and diarrhoea with weight loss.
Constipation may cause colicky abdominal pains due to peristalsis. This is common and not necessarily due to a serious underlying disease.
Pain on passage of stool due to anorectal disease may lead to a deliberate suppression of the urge to defecate and therefore the accumulation of large, dry, hard stools and constipation. This is a common cause of constipation in children.
Occasionally, constipation can present with watery ‘overflow’ diarrhoea, due to increased gut secretions passing around hard stool in the rectum. Alternating constipation and diarrhoea, often with bloating, passage of mucus, and abdominal pains that are relieved by defecation, is commonly due to a functional bowel disorder, e.g. irritable bowel disease. However, it is important to exclude malignancy if patients are over 45 years or there are any suspicious features.