Constipation is an extraordinarily common cause of patient morbidity in the United States.^1,2,3,4 The incidence of constipation increases with age, with 30% to 40% of persons >65 years old citing constipation as a problem.^4,5 Constipation affects as many as 80% of critically ill patients and is directly associated with patient mortality in this population.⁶

Physicians and patients define constipation differently. Physicians have traditionally defined constipation as fewer than three bowel movements per week. In contrast, patients commonly define constipation in terms such as abdominal discomfort, bloating, straining during bowel movements, or the sensation of incomplete evacuation. Consequently, constipation should not be defined simply by stool frequency alone, because doing so maximizes the potential to underdiagnose a significant number of patients who suffer from the condition.⁷ The Rome criteria for the definition of constipation consist of two or more of the following signs or symptoms: (1) straining at defecation at least 25% of the time, (2) hard stools at least 25% of the time, (3) incomplete evacuation at least 25% of the time, (4) fewer than three bowel movements per week, (5) symptoms for at least 12 weeks (consecutive or nonconsecutive) in the preceding 12 months for chronic constipation.⁸

Constipation is a complicated condition with multiple, often overlapping causes (Table 74-1). Gut motility is affected by diet, activity level, anatomic lesions, neurologic conditions, medications, toxins, hormone levels, rheumatologic conditions, microorganisms, and psychiatric conditions. Constipation is best thought of as either acute or chronic, as doing so helps formulate a differential diagnosis. Due to the rapidity of symptom onset, acute constipation is intestinal obstruction until proven otherwise. Common causes of intestinal obstruction include quickly growing tumors, strictures, hernias, adhesions, inflammatory conditions, and volvulus. Other causes of acute constipation include the addition of a new medicine (e.g., narcotic analgesic, antipsychotic, anticholinergic, antacid, antihistamine), change in exercise or diet (e.g., decreased level of exercise, fiber intake, or fluid intake), and painful rectal conditions (e.g., anal fissure, hemorrhoids, anorectal abscesses, proctitis). Chronic constipation can be caused by many of the same conditions that cause acute constipation. However, some specific causes of chronic constipation include neurologic conditions (e.g., neuropathies, Parkinson’s disease, cerebral palsy, paraplegia), endocrine abnormalities (e.g., hypothyroidism, hyperparathyroidism, diabetes), electrolyte abnormalities (e.g., hypomagnesia, hypercalcemia, hypokalemia), rheumatologic conditions (e.g., amyloidosis, scleroderma), and toxicologic causes (e.g., iron, lead).

HISTORY

The differential diagnosis of constipation is broad, so obtain a thorough history. Determine when the symptoms started and then determine whether there are any temporally related clues that can help narrow the differential diagnosis. Was a new medication or dietary supplement added at that time? Was there a decrease in fiber or fluid intake? Was there a change in activity level? Past medical and family history can help shed light on the cause of the constipation. Is there a history of hypothyroidism or diabetes? Does the patient have frequent kidney stones, which would point toward hyperparathyroidism? Although most patients who present with constipation do not have emergent conditions and may be treated symptomatically as outpatients, there are several historical elements that hint to a more ominous cause of symptoms, such as intestinal obstruction. Worrisome findings in addition to constipation include rapid onset, nausea or vomiting, inability to pass flatus, severe abdominal pain and distention, unexplained weight loss, rectal bleeding, unexplained iron-deficiency anemia, or a family history of colon cancer.² Any of these findings should prompt a more rigorous evaluation. Diarrhea alone does not rule out constipation/obstruction, as liquid stool can be passing past an obstructive source.

PHYSICAL EXAMINATION

In addition to a focused abdominal and pelvic examination, a rectal examination is essential. Examine the patient thoroughly for the presence of hernias and abdominal or pelvic masses. Bowel sounds will be decreased in cases of slow gut transit and increased in cases of obstruction. Ascites in the presence of constipation can be a sign of ovarian or uterine neoplasm in postmenopausal women. External rectal examination may demonstrate anal fissures, hemorrhoids, abscesses, or protruding masses. Digital rectal examination is useful in that it may demonstrate fecal impaction or an obstructing rectal mass. Especially common in the elderly is watery stool making its way around an overt impaction. Normal rectal tone is useful in ruling out neurologic causes of obstruction. Any stool retrieved from the rectal vault should be visually inspected and tested for occult blood. The finding of grossly bloody or guaiac-positive stool in the setting of constipation suggests concern for cancer, bowel ischemia, stercoral ulcer, or inflammatory bowel disease.

LABORATORY EVALUATION AND IMAGING

The evaluation of a constipated patient depends on the level of concern for an organic cause of constipation. If the patient is chronically constipated, little is usually gained from any testing so long as the history and physical examination do not point toward an organic cause. If the patient has a history concerning for intestinal obstruction (e.g., acute onset of symptoms, vomiting, significant abdominal distention or pain), an upright chest film and abdominal flat and erect films are useful. In cases of complete or partial intestinal obstruction, these films may demonstrate air-fluid levels or dilated bowel. If there continues to be high clinical suspicion for intestinal obstruction despite a normal chest and abdominal series of radiographs, then abdominal CT with PO and IV contrast may be necessary to make the diagnosis. In cases of suspected fecal impaction, an abdominal film should be obtained (Figure 74-1). In a constipated patient, such a film will demonstrate colonic or rectal dilation with or without air-fluid levels. Normal maximum diameter of the colon is 6 cm, whereas normal maximum diameter of the rectum is 4 cm.² In all patients in whom an organic cause of constipation is suspected, laboratory evaluation should include a CBC and electrolytes. CBC is useful to screen for anemia, and electrolytes are useful to identify hypomagnesia, hypercalcemia, and hypokalemia. Obtain thyroid function tests for suspected hypothyroidism. Obtain serum lead and iron levels for suspected heavy metal toxicity.