Constipation, like diarrhea, is difficult to define with precision due to the wide variation in normal bowel habits. However, because 95% of people have at least three bowel movements per week, for practical purposes constipation can be defined as a condition in which fewer than three stools per week are passed. In addition to infrequent stools, constipation usually carries a connotation of difficulty in passing the stool.
The economic costs of constipation are impressive. In the United States, more than $250 million is spent annually on laxatives. Additional costs of unknown magnitude are incurred in the evaluation of patients for underlying disorders that may predispose to constipation.
Etiology and differential diagnosis
Constipation is a symptom, not a disease. It may develop as a functional condition, in which case it appears to be related to changes in bowel motility; it may be a component of a bowel condition, such as symptomatic diverticular disease or irritable bowel syndrome; or it may result from a specific abnormality or disorder, such as an obstructing cancer of the colon or hypothyroidism (Table DIFFERENTIAL DIAGNOSIS OF CONSTIPATION).
«Functional» constipation occurs with somewhat greater frequency in women and increases in prevalence with age in both sexes. It appears to be influenced by the composition of the diet, particularly the fiber content. Normal daily stool weight in the United States ranges from 100 to 200 g, and the stool is composed of about 80% water. Increasing the dietary fiber increases the stool weight, primarily because of retained water, and increases the stool frequency.
Recent evidence also indicates that several grams of dietary carbohydrates and polysaccharides normally pass undigested to the colon, where they are metabolized by bacteria to osmotically active particles and cathartic agents. Thus, a diet low in complex sugars (e.g., fruits) and carbohydrates may contribute to constipation.
Lack of exercise also is associated with constipation. Whether this is the major predisposing factor to constipation of bedridden patients and the elderly and whether their poor dietary intake of fiber and carbohydrates is an additional important factor are difficult to determine.
One caveat that is important for diagnosis should be mentioned. Some patients with an obstructing lesion, such as a sigmoid carcinoma or a fecal impaction, have diarrhea, characterized by the frequent passage of small amounts of loose or liquid stool. This is because the stool proximal to the obstruction is poorly absorbed and seeps around the obstruction. The physician must be attentive in recognizing such patients to avoid inappropriate treatment with antidiarrheal medications, which would only worsen the underlying disorder.
History. To paraphrase a common saying, «One man’s constipation is another man’s diarrhea.» Thus it is important that the physician determine what the patient means by constipation. How frequently are stools passed? What is their consistency? Is the condition acute or chronic? Are there associated signs or symptoms, such as weight loss, abdominal pain, or blood in the stool?
Constipation of long duration accompanied by crampy abdominal pain without weight loss or systemic symptoms suggests functional constipation, irritable bowel syndrome, or symptomatic diverticular disease. On the other hand, constipation of recent onset, blood in the stool, or change in the stool caliber suggests another causative disorder, such as carcinoma of the lower bowel. A history of calcium channel blocker, anticholinergic, or opiate drug intake should be sought as an explanation for constipation.
|TABLE. DIFFERENTIAL DIAGNOSIS OF CONSTIPATION|
The physical examination may give a clue to systemic disease, such as hypothyroidism or a neurogenic disorder. An abdominal mass may indicate an obstructing lesion or merely firm stool in the colon. The character of the stool itself and the tone of the anal sphincter can be determined by rectal examination.
Most patients who have constipation that is severe enough to cause them to consult a physician require some diagnostic evaluation beyond the history, physical examination, and stool testing for occult blood. The extent of the evaluation varies according to the individual circumstances, but in general, a minimal evaluation of constipation consists of sigmoidoscopy and barium enema or colonoscopic examination. Additional studies may include serum electrolytes, thyroid function studies, blood glucose, and serum calcium.
Anorectal manometry is helpful in making the diagnosis of the rare disorder Hirschsprung’s disease (aganglionosis of the distal colon or rectum). The normal relaxation of the internal anal sphincter is absent in Hirschsprung’s disease when the rectum is distended by stool or a balloon. However, some patients with long-standing constipation in whom the rectal vault remains chronically distended may also have an abnormal rectoanal reflex. The barium enema in Hirschsprung’s disease characteristically shows a narrow rectum, corresponding to the aganglionic segment. For best results, the barium enema should be performed in an unprepared bowel, that is, with stool in the distal colon. Rectal biopsies are of value only if they show the presence of ganglia, thus ruling out Hirschsprung’s disease. Sampling error and failure to obtain deep enough tissue may yield inadequate specimens. The absence of ganglia does not necessarily imply Hirschsprung’s disease, however. If the diagnosis remains in question, a full-thickness surgical biopsy of the rectal wall may be necessary.
Treatment of constipation involves addressing a number of issues, including lifestyle, diet, and medications. If a specific cause of constipation is identified, therapy of course includes treatment of the cause.
Some patients literally do not take time to have a bowel movement. Their busy schedules require frequent cortical inhibition of the urge to defecate. Although it may be difficult to put in practice, simply recognizing the urge to defecate and acting on it may be the first step for many patients in achieving normal laxation. A program of mild exercise (e.g., walking) for sedentary patients may improve constipation.
The average daily intake of crude fiber in the United States is about 4 g. This is roughly one fifth of the daily intake of the native populations of some areas in Africa, who typically have four or five bulky stools per day. Because fiber is hydrophilic, increasing the fiber intake should produce large stools that require more frequent passage.
Dietary fiber can be increased by eating fruits, vegetables, potato skins, and bran-containing foods. Some patients find it easier to consume fiber in the form of raw, unprocessed bran, 1 to 2 tablespoons per day, or a commercial product such as Metamucil. Bran or commercial fiber supplements should be mixed in water or juice before ingestion. Increasing total daily intake of water to 1 to 2 L augments the laxative effects of dietary fiber.
Most patients with chronic constipation have had ample experience with laxatives. Sometimes a vicious cycle develops: Constipation is relieved by laxatives or cathartics; because the bowel has been evacuated, the patient has no urge to pass stool for several days and becomes concerned; the patient perceives constipation again and resumes intake of laxatives.
The chronic use of laxatives is to be avoided, although from time to time a laxative may be necessary to relieve constipation. Perhaps the gentlest agent is mineral oil. Virtually any patient with functional constipation responds to mineral oil, provided enough is given. The initial dosage is 1 tablespoon a day. If that amount is ineffective, the dosage can be increased by 1 tablespoon each day until constipation is relieved, up to a maximum of 4 tablespoons. Mineral oil should be avoided in patients who might aspirate it. Also, it should not be taken chronically because of its interference with the absorption of fat-soluble vitamins.
If a patient has a genuine need for frequent laxation, a reasonable alternative to the traditional laxatives and cathartics is lactulose. Lactulose is a disaccharide that is not absorbed but is metabolized by colonic bacteria to osmotically active particles. It also acidifies the stool by the production of lactic acid. The usual dosage is 1 to 2 tablespoons one to four times daily. Lactulose may also be given in powder form. Polyethylene glycol laxative or Miralax may be used daily to lubricate the stool and relieve constipation. The usual dose is one to four glasses each day.
Impaction of a firm, immovable mass of stool is found most often in the rectum but may occur within the sigmoid or descending colon. Fecal impaction typically develops in elderly, inactive patients, but the differential diagnosis is the same as for ordinary constipation, ranging from functional constipation to hypotonic bowel disorders to distal bowel obstruction (Table DIFFERENTIAL DIAGNOSIS OF CONSTIPATION).
Regardless of the underlying cause, the treatment consists of several approaches. First, the impaction may be broken manually during digital rectal examination. If that attempt is not completely successful, the mass can be softened and evacuated by warm water or saline lavage through a sigmoidoscope or rectal tube. Sometimes mineral oil enemas are useful. Oral mineral oil may be administered if there is no risk of aspiration. Occasionally dilatation of the anus under general anesthesia is used to gain access to the fecal impaction. Rarely, surgical removal of the impaction is necessary.