Constipation is an often-overlooked problem in primary care practice. It deserves careful evaluation, including consideration of the many possible causes and appropriate diagnostic testing. Fortunately, most patients respond well to conservative measures.
Constipation prompts a visit to a physician by 1.2% of the US population every year (although most persons with constipation do not seek the assistance of a physician). (1) The prevalence of constipation increases with age, and is more common among women than men in all age groups. (2,3) It is more frequent among non-whites, and more frequent in colder, poorer, and rural states. (4)
The definition of constipation varies substantially among patients, clinicians, and researchers, and includes infrequent bowel movements, difficult evacuation of feces, inability to defecate at will, and hard feces. Interestingly, the actual frequency of bowel movements does not change with age even when controlled for laxative use--evidence that the meaning of the term constipation involves more than just frequency of bowel movements. (5)
Constipation is caused by a heterogeneous and often overlapping group of disorders. The undigested food that reaches the colon is mixed with fluid and electrolytes, bacteria, and gas. Normal colonic function requires absorption of water, a coordinated combination of segmental contractions that mix stool, propagation of contractions that move feces over short distances, and high-amplitude contractions that move fecal waste longer distances. Defecation entails a synchronized combination of voluntary contraction of striated muscle and involuntary smooth muscle contraction. Anything that limits the fluid content in fecal waste, interferes with the movement of feces through the colon, or interferes with defecation can cause constipation.
Constipation may be classified as primary or secondary, which emphasizes the need to identify and treat underlying systemic disorders before proceeding with the gastrointestinal evaluation (Table 1). However, constipation is often multifactorial in origin. Irritable bowel syndrome (59%) is the most common primary cause of severe intractable constipation, followed by isolated pelvic floor dysfunction (25%), isolated slow-transit constipation (5%), and combined slow-transit constipation and pelvic floor dysfunction (2%). (6) In a study of 190 patients in whom irritable bowel syndrome and other identifiable causes of severe constipation were excluded, 59% had disordered defecation, 27% had slow-transit constipation, and 6% had a combination of these 2 causes. No pathology was identified in about 8% of these patients. (7)
History, physical examination, and baseline laboratory testing identify most secondary causes of constipation (Table 1). Patients in whom no secondary cause is found should undergo colonoscopy, or barium enema and flexible sigmoidoscopy to identify any obstructive lesions. Red flags that suggest significant organic disease include weight loss, frequent nocturnal awakening due to symptoms, blood mixed in stool, and a family history of colon cancer.
A therapeutic trial of a high-fiber diet (or fiber supplements) with or without mild laxatives is reasonable if no secondary or obstructive cause is present. If these measures fail. or if the patient has recurrent constipation, more extensive evaluation is required. Patients in whom a gynecologic cause of constipation is suspected should also be considered...