Author : Dr Uri Ladabaum Professor of Medicine Gastroenterology University of California, San Francisco
2008-04-03
2008-04-03
“I’m constipated” – What does that mean?
Not all people mean the same thing when they use the term “constipation.” In general, “constipation” refers to infrequent or difficult bowel movements. An
individual person’s specific symptoms may differ from another’s, and
may include achieving a bowel movement only every several days,
experiencing difficulty passing stool, having to strain excessively
during a bowel movement, not feeling like a bowel movement has been
complete, passing hard stool, spending too much time trying to have a
bowel movement, needing to use one’s hands to help stool come out, and
trying but failing to have a bowel movement.1-3
It is important for patients and doctors to communicate clearly about what patients mean by “constipation.” There
may be a tendency to focus on how often a person achieves bowel
movements, with at least 3 bowel movements per week being considered
“normal.” But many times patients are bothered by the
multiple symptoms of difficult stool passage, even if they achieve
several bowel movements per week or even every day.
Formal definitions of constipation
The
American College of Gastroenterology Chronic Constipation Task Force
recommended a broad definition of constipation that captures the
symptoms of patients who report that they are constipated:1, 4
“Constipation
is a symptom-based disorder defined as unsatisfactory defecation
[“defecation” is the passing of stool] and is characterized by
infrequent stools, difficult stool passage, or both. Difficult
stool passage includes straining, a sense of difficulty passing stool,
incomplete evacuation, hard/lumpy stools, prolonged time to stool, or
need for manual maneuvers to pass stool. Chronic constipation is defined as the presence of these symptoms for at least 3 months.”
Most
of the time, there is no specific explanation for constipation, and it
is considered “functional,” meaning that symptoms are present without a
clear underlying abnormality. Leading researchers have met
periodically in Rome since the 1980s, and have proposed symptom-based
criteria for the functional gastrointestinal disorders. The
Rome III definition of functional constipation, proposed in 2006, is “a
functional bowel disorder that presents as persistently difficult,
infrequent, or seemingly incomplete defecation, which does not meet
Irritable Bowel Syndrome criteria.”3 Irritable
bowel syndrome, or IBS, is a syndrome characterized by abdominal pain or
discomfort and altered bowel movements, which can include constipation,
diarrhea, or both. Some propose that chronic constipation
and IBS lie along a spectrum, with pain or discomfort being very
prominent in IBS, but milder and rarer in chronic constipation. The
Rome III diagnostic criteria for functional constipation, which are
meant to be used in clinical research but are not practical for clinical
care, are the following:3
1. Must include two or more of the following:
a. Straining during at least 25% of defecations
b. Lumpy or hard stools in at least 25% of defecations
c. Sensation of incomplete evacuation for at least 25% of defecations
d. Sensation of anorectal obstruction/blockage for at least 25% of defecations
e. Manual maneuvers to facilitate at least 25% of defecations (e.g. removal of stool with the fingers, or applying support around the anus with the hand)
f. Fewer than 3 defecations per week
2. Loose stools are rarely present without the use of laxatives
3. There are insufficient criteria for Irritable Bowel Syndrome (IBS)
* Criteria fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis
These
formal definitions highlight the fact that infrequent bowel movements
may be part of the group of symptoms that patients with “constipation”
experience, but are not necessarily the principal feature.
“I only have two bowel movements a week. Should I worry?”
A
common misconception is that a daily bowel movement is necessary for
good health, and that failure to empty stool promptly can lead to
“toxic” consequences for the body.5 The modern
concern with the need to have a daily bowel movement has its root in the
old idea of “autointoxication,” which is the belief that toxins can
form when undigested food stays in the large intestine (the colon) for
too long, and can then be absorbed into the body and cause all kinds of
symptoms and health problems.5 There is no scientific evidence to support these ideas.
It
is important to dispel fear in persons who do not achieve a daily bowel
movement in order to avoid unnecessary interventions such as purges,
enemas, and “cleansing” regimens. Some persons see a doctor out of concern that they have bowel movements only a few times a week, but they actually feel fine. For these patients, it is important to provide reassurance that they do not have a “medical problem.” As discussed below, it is recommended that constipation be treated only when it impairs a person’s quality of life.1
What causes constipation? Are there subtypes of constipation?
Constipation
can be considered “primary” when no clear cause is evident, and
“secondary” when there is an underlying factor or illness that can
explain the constipation. Common causes of “secondary”
constipation include medications (classic examples are the potent pain
medications of the narcotic class, including the opioids codeine and
morphine, but many other medications can also cause constipation),
metabolic diseases such as diabetes, neurologic diseases such as
Parkinson’s disease, and pregnancy. It is recommended that
opioid medications be prescribed with a bowel regimen including stool
softeners or laxatives in order to prevent constipation.
What causes “primary” constipation? When patients with constipation are studied with specialized physiologic tests, some patients demonstrate specific findings.6, 7 A subgroup of patients has very slow passage, or transit, of stool through the colon (slow-transit constipation). In some of these patients, the nerves of the colon may be abnormal. Another
subgroup has difficulty actually pushing out the stool from the rectum
(defecatory disorders, which are referred to by numerous names including
obstructed defecation, pelvic floor dysfunction, pelvic floor
dyssynergia, anismus, and spastic pelvic floor). In these
patients, there may be abnormalities in the muscle and nerve function of
the rectum, anus, and the complex set of muscles in the floor of the
pelvis, all of which must act in coordination to expel stool. A small minority has both slow transit and a defecatory disorder.
A
significant fraction of persons with constipation has normal passage
time through the colon and no obvious abnormality in the nerve and
muscle function needed to expel stool from the rectum (normal-transit
constipation). In these patients, constipation is probably
explained by the perceived difficulty in achieving a bowel movement or
by the presence of hard stools.2
Normal function of the colon, rectum and anus, and abnormalities in constipation
Understanding the normal function of the colon, rectum, and anus6 allows appreciation of the differences between the subgroups of primary constipation.
The
right side of the colon serves to store and mix stool contents, the
left side of the colon serves for storage and as a conduit of stool to
the rectum, and along the length of the colon there is absorption of
salts and water. Thus, the stool content in the right colon is generally looser than in the left colon. There
are several patterns of normal muscle activity in the colon, including
contractions that travel for long distances along the colon,
contractions that don’t seem to travel much, and slow and steady
contractions. Powerful contractions that form a traveling wave down the colon can move stool contents for significant distances. These often occur early in the morning, and are related to the morning bowel movement that is typical for many persons. They can also occur after meals, and explain why some people feel the need to have a bowel movement after eating. During
these after-meal bowel movements, it is not the meal that was just
eaten that is eliminated, but rather stool that has been produced after
previous meals. Persons with slow-transit constipation may
demonstrate abnormalities in the motor activity of the colon, but the
range of “normal” is broad, and there is no single pattern that is
classic for slow-transit constipation.
The rectum is the reservoir at the end of the colon, where stool is present before it is eliminated. The anal sphincter is the ring of muscle just beyond the rectum that prevents stool from leaking out. Most
of the time, pelvic muscles (the puborectalis sling) pull forward on
the rectum, keeping it an angle, and the anal sphincter is contracted. Both of these conditions prevent the passage of stool. The
normal process of having a bowel movement involves relaxation of the
puborectalis sling, thus allowing the rectum to straighten, and
relaxation of the anal sphincter. “Bearing down” increases
the pressure inside the abdomen, and this can help the passage of stool
when the rectum is straight and the anal sphincter is relaxed. Patients with disorders of defecation may exhibit lack of coordination of these functions. For instance, they may bear down while also contracting (instead of relaxing) the puborectalis sling and the anal sphincter. This amounts to “pushing against a closed outlet.”
How common is constipation?
It
is estimated that in North America, 12% to 19% of people have
constipation, and that over 60 million people meet Rome criteria for the
diagnosis of constipation.8 Taking all available studies, the estimates reported for the fraction of the population with constipation ranges from 2% to 27%. These
studies have used different definitions of constipation and different
ways of estimating how common constipation is, which likely explains the
wide range in the estimates. Most patients who report constipation still have the condition one year later.
Research studies have identified subpopulations that are more likely to experience constipation.8 Women are twice as likely as men to have constipation. Non-white persons seem to have a higher rate of constipation. The elderly are more likely than younger persons to suffer from constipation. Constipation is more commonly reported by persons with lower socioeconomic status.
What routine medical tests should be done in patients with constipation?
There are few research studies that address the usefulness of specific tests in the evaluation of patients with constipation.9 The
current consensus is that there is no evidence to support the routine
use of blood tests, x-ray studies, or endoscopy (sigmoidoscopy or
colonoscopy) in persons with constipation.1, 9
In
persons who are age 50 years and older, it is reasonable to offer
screening for colorectal cancer, as is recommended for all persons, even
those without symptoms.1 The available
evidence suggests that persons with chronic constipation who undergo
sigmoidoscopy or colonoscopy (exams of the end portion of the colon or
the entire colon with a flexible tube with a camera at the tip) are
likely to have colon cancer and polyps (growths that could turn into
cancer) at the same rate as persons without symptoms.10
Specialized tests may be useful in persons who have constipation that is difficult to treat. This
is particularly the case when it comes to identifying those persons
with extremely slow colonic transit, or defecation disorders, because
different specific therapies may be offered to these subgroups of
patients.
How should the constipated patient be approached in primary care practice?
Current
expert opinion holds that in younger patients with chronic constipation
and no “alarm signs” or clinical features to suggest a specific
underlying disease, no medical testing is necessary.1, 3, 4 “Alarm
signs” may indicate more serious underlying disease, and it is
recommended that testing be performed in patients with these signs,
which include bleeding from the rectum, weight loss of 10 pounds or
more, family history of colon cancer or inflammatory bowel disease
(ulcerative colitis or Crohn’s disease), anemia (low blood count),
positive fecal occult blood test (hidden blood in the stool), as well as
the acute onset of symptoms in elderly persons.1, 4 Physicians should determine whether individual patients should have blood tests (e.g., to
establish if high calcium or low thyroid hormone levels could be
causing constipation), or other tests including sigmoidoscopy or
colonoscopy. Persons who are candidates for colon cancer
screening, including those who are age 50 years and older, should be
offered screening.1
Treatment of constipation should be based on the severity of symptoms and their impact on a patient’s quality of life.1 First, it must be determined whether the patient is bothered by the “constipation” or only by the idea of “being constipated.” Patients
may be reassured that achieving a bowel movement every several days is
in the range of normal, and that having infrequent bowel movements is
not harmful in and of itself. Those with troubling bowel symptoms should be offered treatment for their constipation.
It
is a popular belief that people with constipation do not have enough
fiber in their diet, do not drink enough water, and do not exercise
enough.5 Although there is not much research in
the area, it seems that fiber intake may not be very different in those
with constipation compared to those without. However, some persons with constipation can improve with fiber supplements, as discussed below. Drinking
more water would not be expected to affect the hardness of stool,
because the small intestine has a very high capacity to absorb water,
and in fact there is no evidence that drinking more fluid can treat
constipation. Some patients report that exercise
regularizes their bowel movements, although there are no good studies
that support this as a treatment for constipation. Regardless, it is good general advice for people to engage in regular exercise.
For
many persons with regular bowel movements, part of their “regularity”
seems to be a behavior pattern that takes advantage of the times when
the colon is normally active, such as in the morning and after meals. Patients
with constipation should be advised to listen to their body and go to
the bathroom when they feel the urge to have a bowel movement,
particularly upon awakening and after eating. They should not spend excessive time in the bathroom straining, however.
What medical treatments are available for constipation?
The
available medical therapies for constipation include bulking agents,
stool softeners, laxatives, enemas, and prescription drugs. Many
of the traditional treatments, including fiber supplements and some
laxatives and stimulants, have not been studied in rigorous clinical
trials.11 Although there is insufficient evidence to make formal recommendations for these treatments in practice guidelines,1
some patients do benefit from these traditional therapies, and it is
reasonable to try these before prescription medications are considered.
Stool bulking agents can bind water and thus may increase the solid as well as the water content of stool. The bulking agents include psyllium products (e.g. Metamucil, Konsyl, Perdiem, and multiple supplements), calcium polycarbophil (e.g. Fibercon), methylcellulose (e.g. Citrucel), wheat dextrin (e.g. Benefiber), and bran. Available
evidence suggests that psyllium increases stool frequency, but there is
insufficient evidence to make firm recommendations about other bulking
agents.1 In clinical practice and in the over-the-counter setting, bulking agents can help some persons with constipation. Bulking agents make some patients feel worse. Bloating, for instance, may worsen. In these persons, the agents should be stopped. There is no reason to increase the dose of these treatments to high levels in those who do not benefit from standard doses.5
There is limited evidence on stool softeners such as docusate sodium (e.g., Colace) or docusate calcium (e.g., Surfak) and some of the results of clinical trials are conflicting. These agents are like detergents that allow water to mix better with stool. Stool softeners may have some, possibly minimal, benefit in constipation.1
There are two major types of laxatives. Osmotic laxatives are substances that tend to stay inside the intestines instead of being absorbed into the body. When
these substances stay in the intestines, they retain fluid, and they
can promote the transit of stool as well as make the stool softer or
even loose. Stimulant laxatives are believed to activate
nerves that control the muscle function of the colon as well as affect
absorption of salts and water, thereby promoting stool transit and
lessening the hardness of stool. Overuse of laxatives can
lead to diarrhea and significant imbalances in the levels of salts in
the blood, so caution must be exercised when using these therapies.
Polyethylene glycol (e.g., MiraLax, GlycoLax) is a well-studied osmotic laxative. Until
recently, this medication was available in the United States only by
prescription, but it is now available over the counter. Several studies have assessed the benefit of polyethylene glycol in constipation.1 Polyethylene glycol has been shown to increase stool frequency and improve stool consistency. Some patients experience bloating, cramping, and nausea with this medication.
Lactulose (e.g., Kristalose,
Chronulac), another osmotic laxative, is a sugar that cannot be
processed by humans, and passes undigested into the colon. Lactulose also improves stool frequency and consistency.1 Colonic bacteria are able to digest lactulose, and this can produce gas and bloating. Sorbitol is a similar agent that is poorly absorbed and can be fermented by bacteria in the colon.
Other osmotic laxatives include magnesium citrate and magnesium hydroxide (milk of magnesia).2 These agents have not been well studied, but in clinical practice, they can be useful in treating constipation. In people with kidney problems, abnormal levels of salts in the blood can develop with these agents.
The stimulant laxatives have not been well studied in clinical trials, but they are commonly used. Many agents are available over the counter. Common beliefs are that these agents can harm the colon in the long term, can make the colon “lazy,” or can be “addicting.” However, there is no evidence to support these notions.5 Many of the stimulant laxatives contain senna (e.g., Ex-Lax, Senokot). Bisacodyl is also common (e.g., Dulcolax, Correctol). Some contain cascara sagrada. These
agents may work best if they are used two or three times a week instead
of daily, in combination with daily non-stimulant laxatives.5 Some patients can be treated successfully with these agents for many years. For these patients, there does not seem to be a compelling reason to stop these agents or switch to another treatment.
Other traditional treatments do not fit into the categories described above. They include mineral oil, suppositories, and enemas. Herbal therapies and teas have not been well studied, and it is often not possible to know what is in these preparations. However, some patients rely on these remedies to manage their constipation.
In
recent years, two new prescription drugs became available for the
treatment of chronic constipation. Tegaserod (Zelnorm) was first
approved for women with constipation-predominant IBS, and later for
women and men with chronic constipation.1, 4 Tegaserod
increases the number of complete, spontaneous bowel movements per week.
The marketing of tegaserod was suspended recently because review of
clinical data revealed more adverse cardiovascular events in patients
treated with tegaserod than in those treated with a placebo (an inactive
substance) in clinical studies. Until recent, selected patientsly,
selected patients could be eligible to participate in a restricted
treatment program (“treatment IND”) for women under the age of 55 years
with constipation-predominant IBS or chronic idiopathic constipation
(“idiopathic” means of unknown origin), who did not have satisfactory
response to other available treatments, and/or patients who had
satisfactory improvement of their symptoms with prior tegaserod
treatment. Patients were excluded for a history, current
diagnosis, or symptoms of cardiovascular ischemic disease, the presence
of any cardiovascular risk factors according to National Institutes of
Health guidelines, or uncompensated depression, anxiety, or suicidal
ideation or behavior. The IND program is not currently available.
The most recently approved medication for constipation in the United States is lubiprostone (Amitiza).12 Lubiprostone increases the number of spontaneous bowel movements per week. Nausea can be a side effect of this medication, but it seems to be less common when the medication is taken with food.
There are medications for other conditions that are recognized to have diarrhea as a side effect. These include colchicine and misoprostol. These medications are sometimes used to treat patients with constipation.
What specialized tests should be considered in patients with constipation that is difficult to treat? How do these affect how patients are managed?
Patients who do not respond to medical treatments for constipation should be referred for specialty evaluation.13, 14 Testing to determine which patients have slow colonic transit6, 7 and which patients have defecation disorders6, 7 is likely to alter their management.
Colonic
transit is commonly measured by asking the patient to swallow a capsule
that contains 24 small rings, or markers, that can be seen on x-ray. An x-ray taken one day later should show the markers in the colon. If they are in the stomach or small intestine, then transit time through the stomach or small bowel is severely abnormal. If
an x-ray taken five days after the capsule is swallowed shows 4 or
fewer markers still left in the colon, this indicates that the person
has normal colonic transit. The rest of the markers will have been passed before the fifth day. If
5 or more markers remain in the colon and they are scattered throughout
the right and left side, this is consistent with slow-transit
constipation. If multiple markers are retained at day
five, but appear to be bunched in the lower left colon (the sigmoid
colon) and rectum, this could indicate a defecation disorder. Other methods to test colonic transit are available, including methods that use a small amount of radioactivity (scintigraphy).
Several tests can be used to assess whether defecation is abnormal. Anorectal manometry is the measurement of the pressures in the anus and rectum at rest and with squeezing. Persons
with abnormal defecation may have pressures in the rectum during
attempted defecation that are too low to overcome the resistance at the
anus.6, 7 The normal physiologic pattern is for
the rectal pressure to increase and the anal pressure to decrease
during attempted defecation. The classic pattern in disordered defecation, or pelvic floor dysfunction, is for the pressure in the anus to also increase.7 Patients
may also have abnormal sensation in the rectum, becoming aware of an
inflated balloon only at larger than normal levels.
In
the balloon expulsion test, patients are asked to push out a balloon
that is placed in the rectum, to simulate the process of passing stool. Most persons with normal defecation succeed in 1 minute or less. If patients are not successful after 3 minutes, they are likely to have a disorder of defecation.7
Disordered defecation is managed with biofeedback in addition to medical treatments.7 Several
sessions are provided in order to help patients retrain themselves to
contract and relax the appropriate muscles in order to achieve more
satisfactory passage of stool.
A
radiologic test called defecography consists of asking the patient to
pass a pasty barium material that simulates soft stool while x-ray
pictures are taken. This allows measurement of whether the
rectum is straightening properly or whether there is an abnormal bulge
in the rectum (rectocele) that may be associated with failure to pass
the paste. Rectoceles are relatively common, and most of the time they do not need to be treated surgically.
Hirschsprung’s
disease is an extreme form of abnormal nerve content of the rectum and
colon, which can involve only a small stretch of the intestine or a
large segment. Normally, inflating a balloon in the rectum
produces a reflex that relaxes the internal anal sphincter (the
rectoanal inhibitory reflex). “Potty training” includes
learning to squeeze the external anal sphincter when stool in the rectum
causes the internal anal sphincter to relax, in order to prevent stool
from passing when it is not socially appropriate. If the
rectoanal inhibitory reflex is not present during anorectal manometry, a
sample of the tissue from the rectum is obtained in order to evaluate
for the possibility of Hirschsprung’s disease, which is treated by
surgically removing the affected segment of non-functioning intestine. This condition is generally, but not always, diagnosed during childhood.
Is there a role for surgery in patients with constipation?
The extreme form of slow-transit constipation is called colonic inertia. In patients with extremely slow colonic transit, removing the colon may be necessary in order to manage their constipation. Patients
who also have extremely slow transit through the small intestine will
not fare as well after colonic resection, and this group must be
approached with caution. Patients should be educated about
the fact that removing the colon is expected to help with the frequency
of bowel movements and the symptoms associated with stool retention. However, if patients also have chronic abdominal pain, the pain may not improve. Persons
with slow-transit constipation as well as disordered defecation must
have treatment of the disordered defecation with biofeedback before an
operation is considered. The currently recommended
operation for colonic inertia is removal of the entire colon, with
attachment of the end portion of the small intestine to the rectum
(colectomy with ileorectal anastomosis).14, 15
Conclusion
Constipation is characterized by infrequent and/or difficult passage of stool. It is a very common condition. Most of the time, it is not associated with an underlying disease. It is not necessary to achieve a daily bowel movement in order to be healthy. Therefore, constipation should be treated only if symptoms are bothersome and affect a person’s quality of life. Routine
medical testing is not necessary in persons with chronic constipation,
but age-appropriate colorectal cancer screening should be offered. Multiple non-prescription treatments and several prescription medications are available. Many
of the traditional treatments for constipation have not been studied
rigorously in clinical trials, but they can be effective and they remain
important alternatives in the treatment of patients. In
persons who do not respond to treatment, specialized testing should be
performed in order to identify persons with disorders of defecation,
which can be treated with biofeedback, and slow colonic transit. The extreme form of slow colonic transit, colonic inertia, can be treated by removing the colon surgically.
USEFUL LINKS
National Digestive Disease Information Clearinghouse (National Institutes of Health)
International Foundation for Functional Gastrointestinal Disorders
American Gastroenterological Association Patient Center
American College of Gastroenterology Patient Information Center
Rome Foundation
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