Functional Bowel Disorders Confused with IBS

Functional Bowel Disorders Confused with IBS

Functional bowel disorders (FBDs) are chronic gastrointestinal disorders that have symptoms in the middle or lower GI tract.  These conditions include irritable bowel syndrome (IBS), functional bloating, functional constipation, and functional diarrhea.  Diagnosis of each of these conditions is based primarily on symptom presentation.  Functional bloating, constipation, and diarrhea may overlap with IBS symptoms, but they are considered separate disorders because of other clinical features.

In order for a condition to be considered a FBD, and to distinguish them from temporary conditions, the following criteria must be met:
* Symptoms must have occurred 6 months or greater before the person presents to a physician
* The person must experience the symptoms for 3 or more days a month during the past 3 months.

IBS is discussed extensively in other articles.  This article discusses the other FBDs that may be confused with IBS, but do not meet the criteria of IBS.

Functional Bloating
Functional bloating is defined as distention of the abdomen that is not caused by another functional bowel or GI disorder.  Bloating is very common, in that 10-30% of people have experienced bloating in the past year.  About 96% of people with IBS experience bloating.  It is more common in women than in men, because it is usually associated with menses.  The typical feature of this bloating is that it (1) occurs during the day, often after a meal and (2) improves or disappears overnight and (3) it can occur in the absence of other disorders.  Frequency of bloating is not included as a criterion in the diagnosis, because bloating is usually experienced in people with other GI conditions, and it has not been researched exclusively.  Sometimes, excessive burping or gas may be present, but these are unrelated to the bloating. Currently there are no physiologic (intolerance to food, weak abdominal muscles, etc.) or psychological factors that are related to bloating.

Treatment is similar, whether functional bloating occurs by itself or with other disorders.  Most treatments are designed to reduce gas, and this may not necessarily reduce bloating.  Tegaserod improves bloating in IBS patients, especially females.  Beano, the over-the-counter solution of B-glycosidase that is sprinkled on foods, has been shown to reduce gas, but not necessarily bloating.  Avoidance of foods that produce gas, weight loss, exercising, or taking probiotics may help.

Functional Constipation
Functional constipation is a FBD that presents with difficult, infrequent, or incomplete defecation.  The following criteria must be met for a person to be diagnosed with functional constipation:
1. Must include 2 or more of the following:
a. Straining during at least 25% of defecations
b. Lumpy or hard stools in at least 25% of defecations
c. Sensation or incomplete evacuation for at least 25% of defecations
d. Sensation of obstruction or blockage for at least 25% of defecations
e. Manual maneuvers to help with at least 25% of defecations
f. Fewer than 3 defecations per week
2. Loose stools are rarely present without the use of laxatives
3. There is insufficient criteria for IBS

Constipation occurs in up to 27% of people.  Initial workup of patients presenting with constipation may include a thorough history and physical examination.  Tests such as colonoscopy, measurement of gut transit time, and plain x-rays may also be used to rule out common causes of constipation, including low dietary fiber intake, intake of constipation-producing medications, hypothyroidism, small bowel obstruction, or colon cancer.

Increased fluid intake and exercise can be used, but their effectiveness has not been proven.  Bulking agents may such as psyllium, methyl cellulose, and calcium polycarbophil are helpful.  Stimulating laxatives (bisacodyl, sodium piscosulphate, or senosides) maybe helpful, but has not been proven.  Tegaserod may also be useful.

Functional Diarrhea
Functional diarrhea is a FBD characterized by loose or watery stools without abdominal pain or discomfort occurring in at least 75% of stools.  Its exact frequency is unknown, because it usually occurs with other disorders such as diarrhea-predominant IBS (IBS-D).  The diagnostic criteria is based on stool form (loose or watery stools) rather than frequency, because persons with hard stools may experience an increased frequency of stools.  Functional diarrhea is distinguished from IBS in that people with IBS typically have the symptoms of intermittent diarrhea and constipation, where as functional diarrhea presents with small volume, frequent bowl movements that are always loose or watery.  A thorough history, physical examination, and imaging studies may identify other causes of diarrhea, such as pseudodiarrhea, lactose intolerance, alcoholism, tropical infections, Crohn’s disease, or inflammatory bowel disease.

Simple restriction of the diet (decreased dairy or caffeine intake), may be helpful.  Antidiarrheals (diphenoxylate or loperamide) taken before meals or before public meetings have proven to be effective.  Alosetron, which slows transit time, may improve diarrhea, however it is expensive and its use restricted.  Cholestyramine also has been shown to be effective.

Longstreth GF, Thompson WG, Chey WD, Houghton LA, Mearin F, Spiller RC. Functional bowel disorders. Gastroenterology. Apr 2006;130(5):1480-1491.