Diagnosis of Irritable Bowel Syndrome

Clinical presentation

Symptoms

Patients with irritable bowel syndrome typically complain of crampy abdominal pain and constipation. In some patients, chronic constipation is punctuated by brief episodes of diarrhea. A minority of patients have only diarrhea. Symptoms usually have been present for months to years, and it is common for patients with irritable bowel syndrome to have consulted several physicians about their complaints and to have undergone one or more gastrointestinal evaluation.

Timing of symptoms

The patient may be able to correlate symptoms with emotional stress, but often such a relation is not evident or becomes apparent only after careful questioning as the physician becomes acquainted with the patient. If abdominal cramps are a feature, they often are relieved temporarily by defecation. Bowel movements may be clustered in the morning or may occur throughout the day, but rarely is the patient awakened at night. Stools may be accompanied by an excessive amount of mucus, but blood is not present unless there are incidental hemorrhoids.

The differential diagnosis is broad, including most disorders that cause diarrhea and constipation. However, there are several features that suggest the diagnosis of irritable bowel syndrome (Table FEATURES SUGGESTIVE OF IRRITABLE BOWEL SYNDROME). Several organic disorders may mimic irritable bowel syndrome and, in fact, may be unrecognized for years in patients who mistakenly have been diagnosed as having irritable bowel syndrome. Patients with lactose intolerance typically have postprandial diarrhea associated with crampy pain. They are healthy in all other respects.

A careful history and a trial of a lactose-free diet usually are sufficient to make a diagnosis. Celiac sprue, Crohn’s disease, and endometriosis also can masquerade as irritable bowel syndrome because of the vagueness of the symptoms in many patients. A clinical history of postprandial abdominal pain suggests the possibility of gallbladder, pancreatic, or peptic disease. Because irritable bowel syndrome may affect the entire digestive tract, belching and symptoms of gastroesophageal reflux and dyspepsia are common in patients with irritable bowel syndrome.

Anorexia, weight loss, fever, rectal bleeding, and nocturnal diarrhea all suggest a cause other than irritable bowel syndrome for the patient’s symptoms. The physician should remember, however, that other gastrointestinal disorders can develop in patients with irritable bowel syndrome, and thus one should be alert to a change in the patient’s complaints.

Physical examination

Patients generally appear healthy, although they may be somewhat tense or anxious. If abdominal pain is a prominent symptom, voluntary guarding may be evident, and sometimes a tender, firm sigmoid colon is palpable. A thorough physical examination, including a rectal examination, is important in the evaluation for a non-irritable bowel syndrome disorder.

Diagnostic studies

Because the diagnosis of irritable bowel syndrome is largely one of exclusion, a number of clinical and laboratory studies should be performed to rule out other treatable disorders. The extent of the evaluation depends on the nature of the patient’s symptoms and the adequacy of previous evaluations.

Again, it is important to note that patients with irritable bowel syndrome are not immune to the development of other gastrointestinal disorders. Thus, the length of time that has elapsed since the last evaluation and the character of the current symptoms affect the decision of whether to proceed again with diagnostic studies.

Routine tests such as a complete blood count, an erythrocyte sedimentation rate, and a stool test for occult blood are appropriate for all patients. If the patient complains of diarrhea, the stool should be examined for leukocytes, ova, parasites, and bacterial pathogens. A flexible fiberoptic sigmoidoscopic examination should be performed in all patients with suspected irritable bowel syndrome, whether or not they complain of diarrhea. This test should be followed by a double-contrast barium enema.

Whether additional diagnostic studies are indicated is a matter of judgment. Because Crohn’s disease can be confused with irritable bowel syndrome, an upper gastrointestinal series with a small-bowel follow-through should be performed in patients with persistent abdominal pain, particularly if they have had some weight loss. If the postprandial pain is predominantly in the upper abdomen, ultrasonography of the gallbladder may be indicated to rule out gallstones. Postprandial pain also raises the possibility of pancreatic disease.

If the clinical context is suggestive of a pancreatic disorder, a serum amylase level and perhaps a computed tomography scan of the abdomen are indicated. A lactose tolerance test may be necessary to confirm lactase deficiency in some patients. Lymphocytic and collagenous colitis can be diagnosed only by colonic mucosal biopsies. Small-bowel biopsy may be indicated to rule out small-intestinal mucosal disease (e.g., celiac sprue, Whipple’s disease, Crohn’s disease, and others).

Jennifer Bowles

Jennifer is a clinical pharmacologist. She helps doctors of all medical specialties choose medications. Jennifer consults about drug dosage, interactions, and side effects.