Irritable Bowel Syndrome

Topic Highlights

●  Irritable bowel syndrome (IBS) is a chronic gastrointestinal illness. 

●  Its characteristic features are abdominal discomfort, bloating, altered bowel function. 

●  This visual presentation explains the many hypotheses in the development of IBS, IBS symptoms, diagnosis, and examines treatment options, including how probiotics may affect gut mucosal cytokines. 

Transcript

Irritable bowel syndrome (IBS) is a chronic gastrointestinal illness that affects up to 15% of a given population. Its high prevalence makes IBS one of the most common medical illnesses. While most people may suffer from a mild form of the disease, a few have severe symptoms that can affect their productivity at work as well as their social life; making it difficult for them to stay outdoors for long periods of time or undertake any travel. Nearly 70% of the cases of IBS occur in women.

The main organs involved in the digestive process are the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus. Other organs like pancreas, liver and gall bladder aid in digestion by emptying their secretions into the intestines.

The main digestive organs are shaped like a hollow tube and have a lining called the mucosa. In the mouth, stomach and intestines, the mucosa has glands that secrete juices that help in digestion. The digestive tract has a muscular wall. The contraction and relaxation of these muscles helps food move down the digestive tract. This movement is called peristalsis. Once food is chewed and swallowed, it reaches the stomach via the esophagus.

In the stomach the food is mixed and broken down into small particles. The partially digested food is then pushed out of the stomach into the small intestine where it is broken down further into molecules that can be absorbed from the intestinal walls into the blood vessels lining the intestines. Peristalsis pushes the remainder of the food, along with all the fluid, into the large intestine, where water is absorbed and the food is converted to stool. The stool is passed out of the body through the bowel movement.

In some cases the contractions may become very slow, causing the food to stay in the intestine for long periods of time, making them hard and dry and resulting in constipation. Alternately, the contractions may be very quick, pushing all the undigested food along with lots of fluid, into the large intestine and rectum, resulting in diarrhea.

Despite the high number of people with IBS, the cause is still unknown. There are several theories put forth indicating various causes for the condition. Some experts believe that IBS is due to a change in the gut's ability to sense pain and discomfort. One theory is that the muscular contractions of the digestive tract controlled by nerves supplying the muscle cells undergo a change and result in abnormal peristalsis.

There are hypotheses that correlate IBS pathophysiology and patient psychology. Depression, anxiety, physical and sexual abuse are some of the psychological factors that are linked with IBS.

Research has also focused on the role of the neurotransmitter serotonin in disease development. serotonin is an important control chemical of the gut since it affects transit. Serotonin has augmenting effects on the intestinal peristaltic reflex.

Some investigators discovered that acute gastroenteritis seemed to precipitate a chronic alteration in bowel function, leading to post-infectious IBS.

One hypothesis that relates bacterial overgrowth in the intestine and IBS focused on bloating, one of the more bothersome symptoms in IBS. A large number of IBS patients seemed to have an abnormal lactulose breath test to suggest the presence of small intestinal bacterial overgrowth. Bacterial overgrowth is a condition whereby the large population of normal bacteria in the colon overpopulates the small intestine, which normally contains much fewer bacteria. This overgrowth alters bowel function and results in bloating.

Other factors that are considered causes of IBS include hormonal changes during or around the time of the menstrual period and a family history of the disease.

The characteristic features of IBS are abdominal discomfort, bloating and altered bowel function that may be accompanied by cramping and excretion of mucous in stools. These symptoms were formulated into a series of diagnostic criteria over the years. They included the original Manning Criteria and later the Rome Criteria. The latest diagnostic criteria for IBS are termed Rome III.

According to Rome III criteria, IBS can be diagnosed based on abdominal discomfort or pain and a marked change in bowel habit for at least 12 weeks that need not be consecutive, for 6-12 months. Abdominal discomfort should be accompanied by any two of the following features:

●  Relieved with defecation and/or

●  Onset associated with a change in frequency of stool and/or

●  Onset associated with a change in appearance of stool

Since the symptoms of IBS are similar to many other diseases, a confirmed diagnosis is made only after eliminating other possible causes. To do this, the doctor will request for a stool test, blood test, a sigmoidoscopy or colonoscopy and X-rays or CT scans of the abdomen and pelvis. In colonoscopy the doctor inserts a thin tube that has a camera attached, into the anus and views the colon from inside.

Dietary and lifestyle changes along with counseling are most often recommended to help reduce the severity or prevent resurgence of symptoms. However, these are not enough for complete symptomatic relief. For relief from symptoms like constipation, over-the-counter fiber supplements like psyllium and methylcellulose can be used.

Antidiarrhoeals like loperamide are recommended for controlling symptoms of diarrhea. Anticholinergics or antispasmodics like atropine and scopolamine are prescribed to relive the pain caused by abdominal spasms or cramps.

Patients with IBS who experience depression or anxiety may be prescribed antidepressants like tricyclics or selective serotonin reuptake inhibitors (SSRIs). Antidepressants not only help with depression, they inhibit neurons that control the nerve impulses in the muscle cells of digestive tract, thus relieving the symptoms of IBS.

For diarrhea and pain, tricyclics like imipramine are prescribed, whereas for constipation and abdominal pain, SSRIs like fluoxetine may be prescribed.

There are two drugs that specifically alter the action of serotonin – Alosetron and Tegaserod. Both the drugs are prescribed only to women who have not responded to other forms of treatment.

Alosetron is prescribed for treatment of IBS with diarrhea. It is an antagonist of the 5-HT3 receptor. It antagonizes serotonin and inhibits the movement of intestines and relaxes the colon, resulting in the food staying in the colon for longer periods, allowing the water to be reabsorbed and reducing diarrhea. Two problems have emerged with the use of alosetron. First, alosetron has such a potent effect on diarrhea that patients often have to stop the drug because they get constipated. The second problem is that a small proportion of patients taking this drug have developed ischemic colitis.

Tegaserod is a serotonin agonist drug and is prescribed for the treatment of IBS with constipation. Tegaserod acts like the neurotransmitter serotonin, activating 5-HT4 receptors and accelerating the gut. It also helps to coordinate the movement of the intestines, resulting in improved motility. Tegaserod was observed to cause cardiovascular or cerebrovascular events in a few patients.

Gut flora play an important role in the pathogenesis of IBS. The most common finding is that IBS patients appear to have a lower number of Lactobacillus species. Use of Bifidobacteria infantis, a probiotic, has demonstrated some efficacy in IBS. Probiotics also normalize the ratio of cytokines with in the lining of the gut.

Dietary and lifestyle changes help in reducing the severity of the symptoms and sometimes in preventing IBS, although it may take a long time to produce results. Eat fiber-rich foods like fruits, grains, vegetables and beans. Drink plenty of water to help with the movement of the intestines.

Foods like dairy products, alcohol, carbonated beverages, nuts, mayonnaise or red meat may aggravate the symptoms; so cut down on them. Eat at regular intervals, preferably at the same time daily to regulate bowel movements. For constipation, eat large, fiber-rich meals that will help the movement of the colon. And for diarrhea, eat small frequent meals. Exercise for 20 minutes daily. It will relieve depression and help improve the movement of the intestines.

In many cases symptoms of IBS are aggravated or brought on by stress. Counseling, biofeedback, progressive relaxation exercises, and deep breathing are a few methods that can be used to relieve or eliminate stress from daily life. A psychiatrist or psychologist can work with an IBS patient to understand how they respond to various stressful events in their lives and counsel them to change the way they respond, thus relieving stress.

Biofeedback is a stress-reducing technique that uses machines to show the patient the increase in muscle tension and heart rate that is brought on by stress. The patient is then taught to reduce these effects on his or her own, without the machine.

For busy professionals, just setting aside 20 minutes at the end of the day to indulge in any relaxing activity like a warm bath or watching TV or reading or listening to music can help relieve stress.

In summary, many hypotheses have emerged on the pathophysiology of IBS. While the development of IBS is likely multifactorial, the role of gut bacteria seems to be gaining traction. Ultimately, the use of antibiotics and/or probiotics may be the next wave of treatment in our understanding of IBS.