What is constipation?
Constipation means different things to different people. For many people, it simply means infrequent stools. For others, however, constipation means hard stools, difficulty passing stools (straining), or a sense of incomplete emptying after a bowel movement. The cause of each of these "types" of constipation probably is different, and the approach to each should be tailored to the specific type of constipation. Constipation can also alternate with diarrhea. This pattern is more commonly considered as part of the irritable bowel syndrome (IBS). At the extreme end of the constipation spectrum is fecal impaction, a condition in which stool hardens in the rectum and prevents the passage of any stool.
The number of bowel movements generally decreases with age. Ninety-five percent of adults have bowel movements between three and 21 times per week, and this would be considered normal. The most common pattern is one bowel movement a day, but this pattern is seen in less than 50% of people. Moreover, most people are irregular and do not have bowel movements every day or the same number of bowel movements each day.
Medically speaking, constipation usually is defined as fewer than three bowel movements per week. Severe constipation is defined as less than one bowel movement per week. There is no medical reason to have a bowel movement every day. Going without a bowel movement for two or three days does not cause physical discomfort, only mental distress for some people. Contrary to popular belief, there is no evidence that "toxins" accumulate when bowel movements are infrequent or that constipation leads to cancer.
It is important to distinguish acute (recent onset) constipation from chronic (long duration) constipation. Acute constipation requires urgent assessment because a serious medical illness may be the underlying cause (e.g., tumors of the colon). Constipation also requires an immediate assessment if it is accompanied by worrisome symptoms such as rectal bleeding, abdominal pain and cramps, nausea and vomiting, and involuntary weight loss. In contrast, the evaluation of chronic constipation may not require immediate attention, particularly if simple measures bring relief. What causes constipation?
Theoretically, constipation can be caused by the slow passage of digesting food through any part of the intestine. More than 95% of the time, however, the slowing occurs in the colon.Medications:
A frequently over-looked cause of constipation is medications. The most common offending medications include:
- Narcotic pain medications such as codeine (e.g., Tylenol #3), oxycodone (e.g., Percocet), and hydromorphone (Dilaudid);
- Antidepressants such as amitriptylene (Elavil) and imipramine (Tofranil)
- Anticonvulsants such as phenytoin (Dilantin) and carbamazepine (Tegretol)
- Iron supplements
- Calcium channel blocking drugs such as diltiazem (Cardizem) and nifedipine (Procardia)
- Aluminum-containing antacids such as Amphojel and Basaljel
In addition to the medications listed above, there are many others that can cause constipation. Simple measures (e.g., increasing dietary fiber) for treating the constipation caused by medications often are effective, and discontinuing the medication is not necessary. If simple measures don't work, it may be possible to substitute a less constipating medication. For example, a non-steroidal anti-inflammatory drug (e.g., ibuprofen) may be substituted for narcotic pain medications. Additionally, one of the newer and less constipating anti-depressant medications (e.g., fluoxetine or Prozac) may be substituted for amitriptylene and imipramine.
Habit: Bowel movements are under voluntary control. This means that the normal urge people feel when they need to have a bowel movement can be suppressed. Although occasionally it is appropriate to suppress an urge to defecate (e.g., when a bathroom is not available), doing this too frequently can lead to a disappearance of urges and result in constipation.
Diet: Fiber is important in maintaining a soft, bulky stool. Diets that are low in fiber can, therefore, cause constipation. The best natural sources of fiber are fruits, vegetables, and whole grains.
Laxatives: One suspected cause of severe constipation is the over-use of stimulant laxatives (e.g., senna, castor oil, and certain herbs). An association has been shown between the chronic use of stimulanat laxatives and damage to the nerves and muscles of the colon, and it is believed that the damage is responsible for the constipation. It is not clear, however, whether the laxatives have caused the damage or whether the damage existed prior to the use of laxatives and, indeed, has caused the laxatives to be used. Nevertheless, because of the possibility that stimulant laxatives can damage the colon, most experts recommend that stimulant laxatives be used as a last resort after non-stimulant treatments have failed.
Hormonal disorders: Hormones can affect bowel movements. For example, too little thyroid hormone (hypothyroidism) and too much parathyroid hormone (by raising the calcium levels in the blood) can cause constipation. At the time of a woman's menstrual periods, estrogen and progesterone levels are high and may cause constipation. However, this is rarely a prolonged problem. High levels of estrogen and progesterone during pregnancy also can cause constipation.
Diseases that affect the colon: There are many diseases that can affect the function of the muscles and/or nerves of the colon. These include diabetes, scleroderma, intestinal pseudo-obstruction, Hirschsprung's disease, and Chagas disease. Cancer or narrowing (stricture) of the colon that blocks the colon likewise can cause a decrease in the flow of stool.
Central nervous system diseases: A few diseases of the brain and spinal cord may cause constipation, including Parkinson's disease, multiple sclerosis, and spinal cord injuries.
Colonic inertia: Colonic inertia is a condition in which the nerves and/or muscles of the colon do not work normally. As a result, the contents of the colon are not propelled through the colon normally. The cause of colonic inertia is unclear. In some cases, the muscles or nerves of the colon are diseased. Colonic inertia can also be the result of the chronic use of stimulant laxatives. In most cases, however, there is no clear cause.
Pelvic floor dysfunction: Pelvic floor dysfunction (also known as outlet obstruction or outlet delay) refers to a condition in which the muscles of the lower pelvis that surround the rectum (the pelvic floor muscles) do not work normally. These muscles are critical for defecation (bowel movement). It is not known why these muscles fail to work properly in some people, but they can make the passage of stools difficult even when everything else is normal.
How is constipation evaluated?
A careful history and physical examination is important in all patients with constipation. There are many tests that can be used to evaluate constipation. Most patients need only a few basic tests. The other tests are reserved for individuals who have severe constipation or whose constipation does not respond easily to treatment.
History: A careful medical history from a patient with constipation is critical for many reasons, but particularly because it allows the physician to define the type of constipation problem. This, in turn, directs the diagnosis and treatment. For example, if defecation is painful, the physician knows to look for anal problems such as a narrowed anal sphincter or an anal fissure. If small stools are the problem, there is likely to be a lack of fiber in the diet. If the patient is experiencing significant straining, then pelvic floor dysfunction is likely.
The history also uncovers medications and diseases that can cause constipation. In these cases, the medications can be changed and the diseases can be treated.
A careful dietary history-which may require keeping a food diary for a week or two-can reveal a diet that is low in fiber and may direct the physician to recommend a high-fiber diet. A food diary also allows the physician to evaluate how well a patient increases his dietary fiber during treatment.
Physical examination: A physical examination may identify diseases (e.g., scleroderma) that can cause constipation. A rectal examination with the finger may uncover a tight anal sphincter that may be making defecation difficult. If a stool-filled colon can be felt through the abdominal wall, it suggests that constipation is severe. Stool in the rectum suggests a problem with the anal, rectal, or pelvic floor muscles.
Blood tests: Blood tests may be appropriate in evaluating patients with constipation. More specifically, blood tests for thyroid hormone (to detect hypothyroidism) and for calcium (to uncover excess parathyroid hormone) may be helpful.
Abdominal x-ray: Large amounts of stool in the colon usually can be seen on simple x-ray films of the abdomen. The more stool that is seen, the more severe the constipation.
Barium enemaA barium enema (lower GI series) is an x-ray study in which liquid barium is inserted through the anus to fill the rectum and colon. The barium outlines the colon on the x-rays and defines the normal or abnormal anatomy of the colon and rectum. Tumors and narrowings (strictures) are among the abnormalities that can be detected with this test.
Colonic transit (marker) studies: Colonic transit studies are simple x-ray studies that determine how long it takes for food to travel through the intestines. For transit studies, individuals swallow capsules for one or more days. Inside the capsules are many small pieces of plastic that can be seen on x-rays. The gelatin capsules dissolve and release the plastic pieces into the small intestine. The pieces of plastic then travel (as would digesting food) through the small intestine and into the colon. After 5 or 7 days, an x-ray of the abdomen is taken and the pieces of plastic in the different parts of the colon are counted. From this count, it is possible to determine if and where there is a delay in the colon. In non-constipated individuals, all of the plastic pieces are eliminated in the stool and none remain in the colon. When pieces are spread throughout the colon, it suggests that the muscles and/or nerves throughout the colon are not working, which is typical of colonic inertia. When pieces accumulate in the rectum, it suggests pelvic floor dysfunction.
Defecography: Defecography is a modification of the barium enema examination. For this procedure, a thick paste of barium is inserted into the rectum of a patient through the anus. X-rays then are taken while the patient defecates the barium. The barium clearly outlines the rectum and anus and demonstrates the changes taking place in the muscles of the pelvic floor during defecation. Thus, defecography examines the process of defecation and provides information about anatomical abnormalities of the rectum and pelvic floor muscles during defecation.
Ano-rectal motility studies: Ano-rectal motility studies, which complement defecography tests, provide an assessment of the function of the muscles and nerves of the anus and rectum. For ano-rectal motility studies, a flexible tube, approximately an eighth of an inch in diameter, is inserted through the anus and into the rectum. Sensors within the tube measure the pressures that are generated by the muscles of the anus and rectum. With the tube in place, the patient performs several simple maneuvers such as voluntarily tightening the anal muscles. Ano-rectal motility studies can help determine if the muscles of the anus and rectum are working normally. When the function of these muscles is impaired, the flow of stool is obstructed, thereby causing a condition similar to pelvic floor dysfunction.
Colonic motility studies: Colonic motility studies are similar to ano-rectal motility studies in many aspects. A very long, narrow (one-eighth inch in diameter), flexible tube is inserted through the anus and passed through part or all of the colon during a procedure called colonoscopy. Sensors within the tube measure the pressures that are generated by the contractions of the colonic muscles. These contractions are the result of coordinated activity of the colonic nerves and muscles. If the activity of the nerves or muscles is abnormal, the pattern of colonic pressures will be abnormal. Colonic motility studies are most useful in defining colonic inertia. These studies are considered research tools, but they can be helpful in making decisions regarding treatment in patients with severe constipation. |
