Constipations
Constipation is a universal affliction of Western civilization. In the United States, this malady accounts for more than 2.5 million physician visits a year. It is among the most frequent reasons for self-medication and is particularly troublesome in the elderly. More than $500 million are spent annually in the United States on laxatives; a survey of Londoners revealed 30% admitting to recent laxative use.
There is no uniform definition of constipation. To some, it means movements that are too infrequent or stools that are too hard. Others complain of incomplete or difficult evacuation. Among normal people, bowel habits vary widely, and perceptions of what constitutes normal function are diverse. Population studies show that most normal people have more than three bowel movements per week, with men likely to have at least five. Stools of less than 35 g daily are well below the lower limit of normal.
The primary physician must be able to uncover any underlying pathology and provide symptomatic relief to those without a structural lesion. The prevalence of excessive laxative use and inadequate dietary fiber intake make it imperative that the physician be knowledgeable about the actions and adverse effects of available laxative preparations in addition to dietary alternatives to their use.
Normal Physiology. The process of elimination of fecal waste requires two processes: filling of the rectum by colonic transport and reflex defecation of stool. Constipation may arise secondary to interference with either of these processes. The time it takes food to reach the anus is partially a function of the amount of fiber in the diet. Normal people placed on a diet containing 15 g of bran fiber per day have twice the number of movements per week of those on an uncontrolled diet. Patients with constipation solely on the basis of low dietary fiber usually have intermittent complaints that fully resolve with alteration of diet alone. Exercise has an important effect on the propulsion of bowel contents. Colonic transit has been observed to be significantly greater in physically active people than in those who get little exercise.
Inactivity. Previously active persons often become constipated when confined to bed on account of illness. Less dramatic, but probably no less important, is the effect of a sedentary life-style; constipation is common in inactive people.
Metabolic and Endocrine Disturbances can slow colonic transport. Hypokalemia, hypercalcemia, hypothyroidism, and diabetes are the most important of these in terms of frequency or potential reversibility. Hypokalemia can produce a generalized ileus and is most often seen in patients who take diuretics. Chronic laxative abuse may also produce hypokalemia; surreptitious use of laxatives and diuretics, self-induced vomiting, a pathologic desire to lose weight, and personality disorder are characteristic of such patients, who present with fatigue and electrolyte disturbances. When constipation is caused by hypothyroidism, other manifestations of the disease are usually present, although sluggish bowel movements may be the presenting complaint. Constipation is a bothersome problem in some patients with diabetes; 20% of those with neuropathy report severe difficulty. Significant hypercalcemia (serum calcium level >12 mg/100 mL) can slow bowel motility.
Mechanical Obstruction from tumor, stricture, or volvulus may be responsible for the new onset of constipation. Cramping abdominal pain and distention in conjunction with a marked change in bowel habits are characteristic. Constipation occurs in more than 50% of patients with colorectal cancers; it is usually a symptom of advanced disease but may be the presenting complaint. Constipation is a more common presentation of Crohn’s disease than is diarrhea because transmural involvement predisposes to scarring and obstruction.
Motor Dysfunction. Constipation may be the predominant symptom of irritable bowel syndrome, a common motility disorder of unknown etiology. Patients complain of chronic abdominal discomfort related to alterations in bowel habits and relieved by defecation. They report irregular bowel movements, often diarrhea alternating with constipation (although one may predominate). Passage of mucus, a sense of incomplete evacuation, and bloating or distention add to the clinical picture.
Drug Use may precipitate constipation. Opiates and agents with anticholinergic activity such as antidepressants are frequently implicated. Calcium-channel blockers may slow down bowel motility, and cholestyramine may induce constipation by binding bile salts. Aluminum hydroxide and calcium carbonate antacids are constipating. The habitual use of laxatives is associated with impaired motor activity. The typical clinical picture is a long history of chronic constipation or a desire to feel “well cleaned out,” followed by increasing laxative dependence, decreasing response, and ultimately a sluggish, poorly contracting bowel. The question of whether a prior underlying motor disorder or actual damage from laxative use is the cause remains unsettled.
Psychiatric Disease and Psychosocial Distress play important roles. An underlying depression is often contributory, and bowel complaints may be one of many somatic symptoms. Patients with irritable bowel syndrome have an increased prevalence of somatization, anxiety, and phobias, which have been linked to triggering disturbances of bowel function. Situational stress appears to play a similar role. The exact mechanisms by which emotional difficulties lead to constipation remain unclear, but their contribution is widely recognized. Disturbances in bowel motility and visceral perception have been documented. Constipation develops in the presence of an excessive degree of nonpropulsive contractions and segmentation of bowel contents. At other times, excessive propulsive activity is noted, typically after meals, resulting in diarrhea.
Neurologic Impairment may present as constipation. Spinal cord injury that leads to compression of the cauda equina can halt bowel motility and also cause urinary retention and incontinence. Multiple sclerosis may compromise bowel function, as can ganglionic abnormalities. In most instances, other neurologic deficits are present. Disease limited to loss of neurons in the bowel wall typically presents as chronic, refractory constipation; it may date from childhood or, as noted above, be associated with long-standing laxative use. A permanently damaged neuromotor apparatus may also occur as a consequence of scleroderma.
Inhibition of the Rectal Defecation Reflex has been documented in cases of painful local anal pathology, neurogenic disease (e.g., Parkinson’s disease, multiple sclerosis), long-term use of laxatives, and voluntary suppression. Patients with this problem are found to have stool packed into the rectal ampulla. Voluntary suppression of the urge to defecate is usually a concomitant of a hectic daily pace or traveling. The resulting intermittent constipation may lead to excessive use of laxatives and enemas and damage to the reflex emptying mechanism.
Inadequate Fluid Intake may play a role, although this is not well established. Water is known to be an effective means of distending the stomach and stimulating intestinal activity. The consistency of stool is a function of how much water it contains, which is a result, in part, of how much is taken in.
Pelvic Floor Dysfunction accounts for some cases of intractable constipation of unknown etiology. It may be a consequence of inadequate relaxation or inappropriate contraction of the puborectalis and anal sphincter muscles, pelvic floor dyssynergy, or both. Patients complain of the need to strain despite a strong urge to defecate. They may also report a persistent uncomfortable sense of rectal fullness and the need to remove stool digitally from the rectum to obtain relief. With pelvic floor dyssynergy, patients find that supporting the perineum helps during a bowel movement.