# The Merck Manual on Constipation



## JeanG (Oct 20, 1999)

This article is interesting because it talks about a few organic causes of constipation, and also IBS. It's good info for us to know: The url is: http://www.merck.com/pubs/mmanual/section3/chapter27/27c.htm Constipation Difficult or infrequent passage of feces, hardness of stool, or a feeling of incomplete evacuation.(See also Encopresis and Constipation under Behavioral Problems in Ch. 262.)Symptoms Fecal impaction, which may cause or develop from constipation, is particularly common in the bedridden elderly and after barium has been given by mouth or enema. The patient has rectal pain and tenesmus and makes repeated but futile attempts to defecate. The patient may have cramps and may pass watery mucus or fecal material around the impacted mass, mimicking diarrhea. Rectal examination discloses a firm, sometimes rocklike, but often rubbery, putty-like mass.Acute constipation occurs when a change in bowel habits produces infrequent stools or hard stools that are difficult to pass. A sudden change suggests an organic cause: Mechanical bowel obstruction must be considered in patients complaining of constipation for only hours or a few days. Adynamic ileus often accompanies acute intra-abdominal disease (eg, localized peritonitis, diverticulitis) and may complicate various traumatic conditions (eg, head injuries, spinal fractures) or may follow general anesthesia. Strong laxatives should be avoided in these circumstances. Acute onset of constipation in bedridden patients (particularly the elderly) is also common. A detailed drug history should be obtained because constipation can be caused by many drugs, including those that act within the lumen (aluminum hydroxide, bismuth salts, iron salts, cholestyramine), anticholinergics, opioids, ganglionic blockers, and many tranquilizers and sedatives.When a change of bowel habit persists for weeks or occurs intermittently with increasing frequency or severity, colonic tumors and other causes of partial obstruction should be suspected. A reduced stool size suggests an obstructive lesion in the distal colon. Local anorectal conditions (eg, anal fissures) that cause pain or bleeding should be sought; plain abdominal x-rays with upright views, proctosigmoidoscopy, and possibly a barium enema may be required. If no disorder is found, treatment should be symptomatic (see below).The common functional causes of chronic constipation hamper normal bowel movements because the storage, transport, and evacuation mechanisms of the colon are deranged. The cause is sometimes a systemic disorder--eg, debilitating infections, hypothyroidism, hypercalcemia, uremia, porphyria--but is more often a local neurogenic disorder--eg, irritable bowel syndrome (see Ch. 32), colonic inertia (see below), megacolon (see Hirschsprung's Disease under Gastrointestinal Defects in Ch. 261). Certain neurologic disorders (eg, Parkinson's disease, cerebral thrombosis, tumor, spinal cord injury) are important extraintestinal causes. Psychogenic factors are most common. Chronic constipation is particularly common in the elderly because of age-related decreases in intrinsic colonic reflexes, low-fiber diets, lack of exercise, and use of constipating medications.Many persons incorrectly believe that daily defecation is necessary and complain of constipation if stool frequency is less than expected. Others are concerned with the appearance (size, shape, color) or consistency of stools, although sometimes the major complaint is dissatisfaction with the act of defecation. As a result, they abuse the colon with laxatives, suppositories, and enemas. Overzealous treatment with laxatives can result in cathartic colon (a "pipe stem" colon lacking haustra on barium enema examination, thus mimicking ulcerative colitis) and melanosis coli (deposits of brown pigment in the mucosa, seen on endoscopy and colonic biopsy).Obsessive-compulsive people try to control anxiety with perfectionistic behavior; their need to rid the body daily of "unclean" wastes may take on exaggerated importance. Depression may be associated with failure to defecate daily. A cycle may develop in which depression reduces stool frequency and failure to defecate augments depression. Such people often become chronic cathartic users or spend excessive time on the toilet.Constipation is blamed for many complaints (abdominal pain, nausea, fatigue, anorexia) that are usually symptoms of an underlying problem (irritable bowel syndrome, depression). Patients should not expect all symptoms to be relieved by a daily bowel movement.Diagnosis Before advising or reassuring a patient about defecatory habits, the physician must exclude serious disease by rectal and sigmoidoscopic examinations and by barium enema when indicated. Everyone with constipation should have a full physical examination, including a rectal examination to exclude masses. CBC, thyroid-stimulating hormone, fasting glucose, and electrolytes are also appropriate for some patients. Those with resistant, prolonged, or unusual symptoms may need colonoscopy. Whenever possible, medications that may cause constipation should be stopped. Individual psychologic needs should be considered.Treatment Agents used to treat constipation are summarized in Table 27-2. The diet should contain enough fiber to ensure adequate stool bulk. Vegetable fiber, which is largely indigestible and unabsorbable, increases stool bulk; certain components of fiber also absorb fluid into the solid phase, making stools softer and facilitating their passage. Fruits and vegetables are recommended, as are cereals containing bran taken to tolerance. Unrefined miller's bran (16 to 20 g; 2 to 3 tsp bid or tid) on fruit or cereal may be preferred.Laxatives should be used carefully. Some may interfere with absorption of various drugs by binding them chemically (eg, tetracycline, Ca, phosphate) or physically (eg, digoxin on cellulose matrices). Rapid fecal transit may rush some drugs and nutrients beyond their optimal absorptive locus. Acute abdominal pain of unknown origin, inflammatory bowel disorders, intestinal obstruction, GI bleeding, and fecal impactions contraindicate laxative and cathartic use.Bulking agents (eg, bran, psyllium, calcium polycarbophil, methylcellulose) provide fiber and are the only laxatives acceptable for long-term use. They act slowly and gently and are the safest agents for promoting elimination. Proper use involves gradually increasing the dose--best taken tid or qid with sufficient liquid (by adding 20 oz/day of extra fluid) to prevent impaction of inspissated medication--until a softer, bulkier stool results. This approach produces natural effects and is not habit forming. Bulking agents normalize both constipation and diarrhea.Wetting agents (detergent laxatives [eg, docusate]) soften stools, making them easier to pass. They break down surface barriers, allowing water to enter the fecal mass to soften and increase its bulk. Increased bulk may stimulate peristalsis, which moves the softened stool more easily. Mineral oil softens fecal matter, resulting in more easily passed stool mass, but it may decrease absorption of fat-soluble vitamins. Wetting agents and mineral oil act slowly; either may be useful after MI or anorectal surgery and when prolonged bed rest is required.Osmotic agents are used to prepare patients for some diagnostic bowel procedures and occasionally to treat parasitic infestations. They contain poorly absorbed polyvalent ions (eg, Mg, phosphate, sulfate) or carbohydrates (eg, lactulose, sorbitol) that remain in the bowel, increasing intraluminal osmotic pressure and drawing water into the intestine. The increased volume stimulates peristalsis, which moves the water-softened stool easily through the bowel. These agents usually work within 3 h.Mg and phosphate are partially absorbed and may be detrimental in some conditions (eg, renal insufficiency). Na (in some preparations) may adversely affect heart failure. These drugs in large or frequent doses may upset the fluid and electrolyte balance in patients without underlying disease. Another approach to cleansing the bowel for diagnostic tests or surgery uses large volumes of a balanced osmotic agent (eg, polyethylene glycol-electrolyte solution).Secretory or stimulant cathartics (eg, senna and its derivatives, cascara, phenolphthalein, bisacodyl, castor oil) are often used to cleanse the bowel for diagnostic tests. They act by irritating the intestinal mucosa or by directly stimulating the submucosal and myenteric plexus. Some are absorbed, metabolized by the liver, and returned to the bowel in bile. Peristalsis and intraluminal fluid both increase, with cramping and passage of semisolid stool in 6 to 8 h. With continued use, melanosis coli, neuronal degeneration in the colon, "lazy bowel" syndrome, and serious fluid and electrolyte disturbances may occur.Fecal impaction is treated with enemas of warm (43.3ï¿½ C [110ï¿½ F]) olive oil 60 to 120 mL (2 to 4 oz) followed by small enemas (100 mL) of commercially prepared hypertonic solutions. If these fail, manual fragmentation and disimpaction of the mass are necessary. These procedures are painful, so peri- and intrarectal application of local anesthetics (eg, lidocaine 5% ointment or dibucaine 1% ointment) is recommended. Some patients require general anesthesia.Explanation is important, but it is of little benefit to try to convince an obsessive-compulsive patient that his attitude toward defecation is abnormal, although psychotherapy may help inculcate more rational ideas. Physicians must inform patients that daily bowel movements are not essential, that the bowel must be given a chance to function, that frequent laxatives or enemas (> once/3 days) deny the bowel that chance, and that the way to "cure a stool" that is "too thin" or "too green" is to avoid looking at it.COLONIC INERTIA(Atonic Constipation; Colon Stasis; Inactive Colon)Diminished colonic peristalsis or rectal insensitivity to fecal masses.Etiology Colonic inertia occurs in elderly or invalid patients, especially if bedridden. The colon does not respond to the usual stimuli that promote evacuation, or accessory stimuli normally provided by eating and physical activity are lacking. Inertia sometimes occurs in patients whose rectal sensitivity to fecal masses is dulled by habitual disregard of the urge to defecate or by prolonged dependence on laxatives or enemas, often initiated in childhood. Drugs frequently compound the problem. Fecal impaction is common.Symptoms, Signs, and Diagnosis The principal symptom is constipation without abdominal discomfort. The urge to defecate is decreased, and stools are often putty-like or soft and not scybalous. Rectal examination frequently discloses an ampulla full of feces, yet the patient has no urge to defecate and cannot do so effectively, even with effort. Proctoscopic and barium enema examinations are normal, although evacuation of the contrast medium may sometimes be difficult and the colon may appear unusually redundant and capacious.Treatment Treatment is adapted to the patient's general status. When possible, exercise should be started. Because abdominal distress and other signs of bowel irritability are minimal, the use of osmotic laxatives (eg, milk of magnesia 15 to 30 mL or sodium sulfate 15 g in 1/2 glass of water) to treat an elderly or invalid patient is harmless. Lactulose syrup (beginning at 10 to 20 mL [2 to 4 tsp] once daily and increased to tolerance and development of softer stools) can also be used. Sorbitol solution at the same dosage is a less expensive alternative. The patient should try to move the bowel at the same time daily, preferably 15 to 45 min after breakfast, because food ingestion stimulates colonic motility. Initial efforts at regular, unhurried bowel movements may be aided by rectal instillation of 60 to 90 mL (2 to 3 oz) of warm (43.3ï¿½ C [110ï¿½ F]) olive oil or isotonic saline (see fecal impaction above) or by glycerin suppositories.DYSCHEZIA(Disordered Evacuation; Dysfunction of Pelvic Floor/Anal Sphincters)Difficulty in defecating, resulting from a lack of coordination of pelvic floor muscles and anal sphincters.Etiology Constipation is caused not only by slow movement through the whole large bowel but also by disturbance of coordinated movements needed for evacuation. Evacuation requires relaxation of the pelvic floor muscles and anal sphincters; otherwise, efforts to defecate will be futile even with severe straining. Pelvic floor dysfunction is a major reason why constipated patients fail to respond to laxatives.Symptoms, Signs, and Diagnosis The patient may sense that stool is present but cannot defecate, even with prolonged straining and digital evacuation. Stools that are not hard may be difficult to pass. Rectal and pelvic examinations show hypertonia of the pelvic floor muscles and anal sphincters, with incomplete voluntary relaxation (anismus) or excessive relaxation (descending perineum). A rectocele or enterocele may be associated but is usually not of prime pathogenic importance. When advanced, a solitary rectal ulcer or varying degrees of rectal prolapse caused by excessive straining may be found. Special x-rays (defecatory proctography) and functional tests of the pelvic floor may locate anatomic abnormalities.Treatment Treatment with laxatives is unsatisfactory. Dyschezia should be considered when standard measures directed toward colonic inertia are unsuccessful. Relaxation exercises and biofeedback can help, although a group approach (physiotherapists, dietitians, behavior therapists, gastroenterologists) may be needed. [This message has been edited by JeanG (edited 09-21-2000).][This message has been edited by JeanG (edited 09-21-2000).]


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