Irritable bowel syndrome, or IBS, is a functional disorder of the colon characterized by symptoms such as abdominal pain, altered bowel habits, bloating, passing mucus and sensation of incomplete defecation. According to the American College of Gastroenterology, doctors diagnose most cases of IBS on the basis of history, physical examination and, sometimes, blood tests. Atypical symptoms require additional evaluation through diagnostic tests such as barium enema, computerized axial tomography and colonoscopy to rule out more serious conditions. Atypical symptoms follow three basic patterns.
Nocturnal Incidence
According to Dr. Chung Owyang, chief of gastroenterology for the University of Michigan Health System and contributor to the prestigious medical reference book "Harrison's Principles of Internal Medicine," abnormal muscle contractions within the muscular lining of the colon cause both pain and alteration in bowel habits for people with IBS. However, these contractions occur almost exclusively during waking hours, as do symptoms of IBS. Abdominal pain and diarrhea that result in sleep interruption are considered atypical features of IBS, although they are often associated with more serious conditions such as colorectal cancers and malabsorptive diseases.
Progressive Course
Doctors use the term progressive to describe symptoms that become worse over time. Without treatment and sometimes even despite treatment, most chronic diseases become worse over time. Functional disorders like IBS, by contrast, remain the same. This doesn't mean that IBS patients don't experience periodic exacerbations in response to triggers. In fact, according to the National Institutes of Health, common triggers include stress or, for women, menstrual periods. However, when the trigger is removed, symptoms of IBS return to baseline. Symptoms that don't conform to this pattern suggest something other than IBS.
Systemic Symptoms
Systemic symptoms such as fever, unintentional weight loss, fatigue and weakness also argue against the diagnosis of IBS. While these are common features of cancer, gastrointestinal infections and malabsorptive diseases, they simply don't occur with IBS. According to Owyang, patients with IBS typically maintain their weight, even in cases of severe IBS. Fever is also uncommon, except in the case of concurrent infection such as the flu or a cold. Fatigue and weakness can result from infections, or they may be signs of anemia. Blood loss should not occur with IBS, but it is a common feature of colorectal cancer and inflammatory bowel disease.
References
- American College of Gastroenterology: Understanding Irritable Bowel Syndrome
- "Harrison's Principles of Internal Medicine;" Irritable Bowel Syndrome; C. Owyang, A.S. Fauci et al.; 2008
- National Institutes of Health: What I Need to Know About Irritable Bowel Syndrome
