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University of Iowa College of Medicine and University of Iowa Hospitals and Clinics Iowa City, Iowa
Constipation accounts for more than 2.5 million patient visits to physicians each year. In 1994, $840 million was spent on laxatives alone. Many patients self-treat their ""constipation,"" either by using home remedies or by using laxatives, and often successfully. Hence, those who seek medical help merely constitute the tip of the ""constipation iceberg."" Most patients have a significant problem that requires a thoughtful appraisal.
Constipation is a symptom, not a disease. It may be defined as the occurrence of two or more of the following symptoms for at least 12 months in a person who is not using laxatives: fewer than three bowel movements per week, excessive straining during at least 25% of bowel movements, a feeling of incomplete evacuation after at least 25% of bowel movements, and the passage of hard or pellet-like stools during at least 25% of bowel movements. Because patients may complain of one or more of the aforementioned symptoms, the physician must determine the exact nature of the problem.
Constipation is often caused by a primary disturbance of colonic or anorectal neuromuscular function, but many other common conditions, including drugs, may lead to this problem (Table 1) . Patients with depression, anorexia nervosa, and other psychiatric conditions also develop profound disturbances of gut motor function, including constipation.
If secondary causes (see
Table 1)
can be excluded, most patients have idiopathic constipation, which
is a functional and essentially a colorectal motility disorder. At least two
subtypes have been recognized, although there is overlap.
Slow transit constipation is characterized by prolonged delay of stool transit through the
colon. This delay may
A systematic and detailed history is extremely important. This should include an assessment of the duration, severity, onset, and precipitating event or events and an assessment of stool frequency, stool consistency (hard, formed, or soft), stool size (small, pellet-like or long column), degree of straining, a sensation of incomplete evacuation, and the need for digital disimpaction of stool. A history of repeatedly ignoring ""a call to stool"" and a history of travel or frequent changes in lifestyle, including shift work, are all important. Dietary history should include the amount of fiber and fluid intake, the number of meals per day, and the time of day when meals are consumed. In the elderly, stool impaction and overflow may manifest as fecal incontinence.
A thorough examination, including a neurologic evaluation, should be performed to exclude systemic illnesses or abdominal masses that cause constipation. During digital rectal examination, it is important to ask the patient to bear down as if to defecate. Normally, one should perceive relaxation of the external anal sphincter together with perineal descent. If these are absent, one should suspect functional obstructive defecation.
The first step is to exclude an underlying metabolic or pathologic disorder. A complete blood count, biochemical profile, serum calcium and glucose levels, and thyroid function tests are usually sufficient. Other investigations may include the following:
This evaluation may help to detect mucosal lesions or abnormalities such as carcinoma, stricture, anal fissure, solitary rectal ulcer, diverticulosis, or proctitis.
An assessment of colonic transit time enables the physician to understand better the rate of stool expulsion from the colon. This is particularly useful, because the patient s recall of stool habit is often inaccurate. The single capsule technique, which consists of administering one Sitzmarks capsule (Konsyl Pharmaceuticals, Fort Worth, TX) containing 24 radiopaque markers on day 1 and obtaining a plain radiograph of the abdomen on day 6 (i.e., 120 hours later), is usually adequate. The radiograph may reveal one of three patterns: normal transit, which consists of either no markers or fewer than 5 markers; slow transit, which consists of more than 5 markers that are scattered throughout the colon; or obstructive defecation pattern, which consists of more than 5 markers in the rectosigmoid region with a near normal transit through the rest of the colon.
This procedure is performed by placing 150 mL of barium paste into the patient s rectum and by imaging the rectum with videofluoroscopy. When the patient tries to evacuate the barium, the morphologic and functional changes that occur in the anorectum are observed. This test provides useful information regarding abnormalities such as rectocele, intussusception, and rectal prolapse.
This test provides a comprehensive assessment of rectal sensation, rectoanal reflexes, rectal compliance, and anal sphincter pressures. Manometric abnormalities that are seen in patients with constipation include impaired rectal contraction, paradoxical anal contraction, absent rectoanal inhibitory reflex, and impaired rectal sensation.
When a balloon is distended in the rectum, there is reflex relaxation of the internal anal sphincter--rectoanal inhibitory reflex. This reflex is mediated by the myenteric plexus and is absent in patients with Hirschsprung s disease. Manometry may also detect abnormalities during maneuvers that simulate the act of defecation. Normally, when a subject bears down, there is a rise in intrarectal pressure associated with relaxation of the external anal sphincter. Inability to perform this coordinated movement represents the chief pathophysiologic abnormality in patients with functional obstructive defecation (anismus), a common cause of constipation.
The first step is to elucidate an underlying cause or mechanism by performing appropriate tests as outlined earlier. An algorithmic approach to constipation is shown in Figure 1 . It is worth reiterating that constipation is a common adverse effect of many drugs, a fact that is often overlooked. Some drugs have anticholinergic effects, others desiccate stool, and others affect rectal sensation and reduce awareness for stooling.
This should include instruction regarding normal bowel habits, diet, fluid intake, and exercise. Those who believe that bowels must move every day should be informed that a bowel movement every other day or sometimes every third day is not abnormal. Patients with poor eating habits, such as those who miss meals, should be encouraged to eat more regularly. Patients with inadequate fiber intake should be advised with the help of a dietitian to increase their intake of natural fiber with fruits and vegetables. It is useful to emphasize that 20 to 30 grams of fiber per day are essential to facilitate bowel movement. However, not every patient with constipation will benefit from a high-fiber diet. In one study, constipated patients who had either slow transit or pelvic floor dysfunction responded poorly to a diet containing 30 grams of fiber per day, whereas patients without an underlying motility disorder either improved or became symptom free. Thus, fiber intake may not be a panacea for all patients. Patients with sedentary habits should be encouraged to exercise or at least increase their physical activity. However, the benefit of exercise for patients with constipation is controversial.
Before labeling a patient as having slow-transit constipation, it is important to exclude pelvic floor dysfunction. Ideally, slow-transit constipation should be treated with a prokinetic agent that selectively stimulates colonic peristalsis. Unfortunately, such an
Figure 6-1 An
algorithmic approach to the management of constipation.
(From Rao SSC: Manometric evaluation of constipation--Part I. The
Gastroenterologist 4:145-154, 1996.)
These laxatives consist of natural substances such as psyllium (Metamucil) or synthetic polysaccharides such as methylcellulose (Citrucel). These compounds resist digestion and retain water. Hence, they increase stool bulk and enhance colon transit. Because fermentation of psyllium can cause bloating and gas in some patients, nonfermentable products such as methylcellulose may be preferable. It is important to emphasize that fiber supplements should be accompanied by a generous intake of fluid. If not, the large bulky stool may become more difficult to expel. Because patients with chronic renal failure or heart failure are on fluid restriction, bulk laxatives are not advisable.
These agents serve as anionic surfactants, that is, they can lower the surface tension of stool. This allows easy mixing of the fatty and aqueous contents of stool, and the softened stool permits easy defecation. The two most popular compounds are docusate sodium (Colace) or docusate calcium (Surfak).
These include agents such as milk of magnesia, calcium citrate (Citracal), magnesium sulfate, sodium phosphate (Fleet Phospho-Soda), and those that contain a mixture of sodium and potassium salts or polyethylene glycol. These hyperosmolar salts exert an osmotic effect in the small bowel and the colon. This draws fluid into the lumen and increases intraluminal volume. Because up to 20% of magnesium can be absorbed, one should exert caution when treating patients with renal disease.
This type of laxative includes lactulose (Cephulac, Chronulac), lactitol, sorbitol, mannitol, and polyethylene glycol solutions (Colyte, GoLYTELY, or NuLytely). Lactulose is a nonabsorbable disaccharide that passes unchanged through the stomach and small bowel and is fermented by anaerobic bacteria in the colon to produce fructose, galactose, short chain fatty acids, and gases. Similarly, sorbitol and mannitol are sugars that are poorly absorbed. In addition to diarrhea, all of these agents can cause bloating, distention, flatulence, and crampy discomfort.
This group includes compounds such as anthraquinolones (cascara), senna (Senokot), bisacodyl (Dulcolax), castor oil, and phenolphthalein (Modane). If possible, one should avoid these agents. They act through a variety of mechanisms, but their net effect is to stimulate intestinal motility and secretion. They also reduce net absorption of fluid and electrolytes, which can lead to significant electrolyte disturbance. Some of these agents, particularly the anthraquinolones, have been reported to cause melanosis coli, a brownish pigmentation of the colonic mucosa.
This problem is best treated by neuromuscular conditioning and biofeedback techniques. The goal of biofeedback therapy is to restore a normal pattern of defecation. Patients with impaired rectal contraction
Patients with stool impaction or those with hard stools that are difficult to expel require digital disimpaction. This can be painful and may require sedation or anesthesia. Once the hard pellets have been removed, these patients require a bowel conditioning regimen of enemas, laxatives, and suppositories (glycerin or bisacodyl).
In debilitated or neurologically impaired patients, a tap water, sodium phosphate (Fleet Enema) enema, or milk of molasses enema may be required to facilitate defecation. If the aforementioned measures fail, particularly in patients with slow transit constipation, surgery may be an option. However, before considering surgery, each patient must be carefully evaluated to exclude generalized neuromuscular dysfunction of the gut. Surgical options for refractory constipation include colectomy with ileostomy or an ileoanal pouch or a cecostomy. However, surgery should be regarded as a last resort for patients with constipation.
Constipation is a common clinical problem that is often misdiagnosed and inadequately managed. Today, technical advances, together with a better understanding of the underlying mechanisms, have led to real progress in the diagnosis and treatment of this condition.
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