10. Constipation / W.G. Thompson

Costiveness, obstipation.   

TABLE 1. Causes of chronic constipation

Constipation defies accurate definition. What is "normal" frequency? Ninety-five percent or more of the population have between three movements per day and three movements per week. Some people consider that fewer than three movements a week without discomfort or dissatisfaction is normal. The effort needed to pass the stool and the consistency of the stool are probably of greater importance. Most would agree that hard bowel movements that are difficult to pass constitute constipation even if they occur as often as daily. One definition of constipation is the need to strain at stool on more than 25% of occasions. Thus constipation may be defined as persistent symptoms of difficult, infrequent or seemingly incomplete evacuation. 

The causes of constipation are summarized in Table 1; organic causes are discussed elsewhere in this text. The commonest kind of constipation is that associated with the spastic colon type of irritable bowel. In this instance, the stool is hard, difficult to pass, and often scybalous (i.e., like rabbit stools or sheep stools). Frequently, passage of such stools is accompanied by abdominal pain. 

Some other functional causes of constipation are difficult to define. In simple atonic constipation, stool in the rectum fails to stimulate the defecation reflex. That is, a full rectum fails to initiate the evacuating response of the internal sphincter. In others, there is no gastrocolonic response to a meal. Still others are part of a generalized motility disorder called chronic idiopathic intestinal pseudo-obstruction. This disorder may be confined to the colon, but often affects other parts of the gastrointestinal tract. In this group must be included problems associated with long-standing use or abuse of laxatives. It is not certain whether the laxative use causes or results from the motility disorder. 

The physician’s questions should elicit details about the nature of the stool. The presence of hard, pellet-like, difficult-to-pass stools, sometimes with a little bit of blood coating the edge, in an otherwise healthy young person strongly suggests the irritable bowel syndrome. On rectal examination or sigmoidoscopy the rectum is often empty or contains only scybala. This type of constipation is often interspersed with periods of normalcy or diarrhea. 

The atonic type of constipation, on the other hand, is associated with a full colon and/or rectum. Often, examination of the abdomen reveals distention, and one may palpate large amounts of stool in the more proximal colon. 

Various sensory or anorectal dysfunctions may also cause constipation. 

Constipation and blood mixed with the stool raise the possibility of an obstructing lesion, such as a carcinoma. Hirschsprung’s disease may present in adults, although usually there is a history of childhood disability. Other possibilities include a spinal lesion, hypothyroidism, hypercalcemia or drug use (e.g., opiates). 

Sigmoidoscopic examination using either the rigid or flexible instrument is necessary to rule out local diseases such as fissures, fistulas or distal proctitis. Many cancers are within the range of the sigmoidoscope. One might also detect melanosis coli, a pigment in the rectal mucosa that indicates chronic laxative use. 

If the constipated patient is over 40, has blood or pus in the stool, or has had significant weight loss, a barium enema is indicated to rule out polyps, cancer or Crohn’s disease of the colon.

A gut transit study may be revealing. Twenty radiopaque markers are ingested and daily plain abdominal x-rays are taken. If 80% of the markers have disappeared in five days, the transit time is said to be normal. In cases of longer transit, the position of the markers may help distinguish colonic inertia from anorectal disorder. More sophisticated studies are then required. 

Obviously, the best management of constipation is to treat any underlying disease. For the spastic type of irritable colon, a good response can be expected if sufficient bulk is added to the diet. It is best to avoid the chronic use of stimulant laxatives because of their potential to damage the myenteric plexus in the colon. If overused, laxatives may cause excessive loss of fluids and electrolytes. Colonic inertia or anorectal dysfunction causing severe constipation or obstipation requires specialist care.