Constipation and Fecal Impaction

Constipation, like diarrhea, is difficult to define with precision due to the wide variation in normal bowel habits. However, because 95% of people have at least three bowel movements per week, for practical purposes constipation can be defined as a condition in which fewer than three stools per week are passed. In addition, patients may experience difficulty in passing stools, may use manual maneuvers (i.e., digital disimpaction, pressing on the perineum and/or lower abdomen), and may complain of hard and lumpy stools.

The economic costs of constipation are impressive. In the United States, more than $250 million is spent annually on laxatives. Additional costs of unknown magnitude are incurred in the evaluation of patients for underlying disorders that may predispose to constipation.

I. ETIOLOGY AND DIFFERENTIAL DIAGNOSIS.

Constipation is a symptom, not a disease. It may develop as a functional condition, in which case it appears to be related to changes in bowel motility or pelvic floor dysfunction; or it may be a secondary condition, such as symptomatic diverticular disease or irritable bowel syndrome; or it may result from a specific abnormality or disorder, such as an obstructing cancer of the colon or hypothyroidism or other causes as listed in Table 36-1.

A. Diet.

Functional or idiopathic constipation occurs with somewhat greater frequency in women and increases in prevalence with age in both sexes. It appears to be influenced by the composition of the diet, particularly the fiber and fluid content. Normal daily stool weight in the United States ranges from 100 to 200 g, and the stool is composed of about 80% water. Increasing the dietary fiber and fluid intake increases the stool weight, primarily because of retained water, and increases the stool frequency.

Recent evidence also indicates that several grams of dietary carbohydrates and polysaccharides found in fruits and vegetables normally pass undigested to the colon, where they are metabolized by bacteria to osmotically active particles and cathartic agents. Thus, a diet low in fruits and vegetables may contribute to constipation.

B. Lack of exercise

also is associated with constipation. It’s difficult to determine whether this is the major predisposing factor to constipation of bedridden patients and elderly people and if their poor dietary intake of fiber, carbohydrates, and fluids is an additional important factor.

C. Colonic obstruction.

Some patients with an obstructing lesion, such as a sigmoid carcinoma or a fecal impaction, may have diarrhea (overflow diarrhea), characterized by the frequent passage of small amounts of loose or liquid stool. This is because the stool water proximal to the obstruction is poorly absorbed and seeps around the obstruction. The physician must be attentive in recognizing this condition in such patients to avoid inappropriate treatment with antidiarrheal medications, which would only worsen the underlying disorder.

II. DIAGNOSIS

A. Clinical presentation

1. History.

To paraphrase a common saying, “One man’s constipation is another man’s diarrhea.” Thus it is important that the physician determine what the patient means by constipation. How frequently are stools passed? What is their consistency? Is the condition acute or chronic? Are there associated signs or symptoms, such as weight loss, abdominal pain, or blood in the stool?

TABLE 36-1 Differential Diagnosis of Constipation

“Functional” constipation
Conditions in which constipation is part of the symptom complex
	Irritable bowel syndrome
	Symptomatic diverticular disease
	Disorders of bowel muscle function (e.g., pseudoobstruction, myotonic dystrophy, systemic sclerosis)
Disorders that can cause constipation
	Endocrine-metabolic conditions (e.g., diabetes, hypokalemia, hypothyroidism, hypercalcemia, pregnancy)
	Bowel obstruction (e.g., neoplasm, benign stricture, ischemic colitis, surgical stenosis)
Disorders causing painful passage of stool (e.g., proctitis, anal fissure)
Neurogenic disorders (e.g., Hirschsprung’s disease [aganglionosis], autonomic neuropathy, multiple sclerosis, Parkinson’s disease)
Drugs (e.g., calcium channel blockers, nitrates, anticholinergics, antidepressants, opiates)