Introduction:
Irritable bowel syndrome (IBS) is a chronic medical problem that effects up to 22% of the population.
Further data indicates that up to 50 percent of patients who present to a gastroenterologist's office for further evaluation of symptoms has irritable bowel syndrome.
In the past, diagnosis of irritable bowel syndrome was a diagnosis of exclusion. That is, other medical problems were eliminated first. Although this is still part of an evaluation, investigators have developed a set of criteria which assist physicians in the diagnosis of irritable bowel syndrome. These are called the Rome Criteria.
Presentation:
Patients with irritable bowel syndrome often have fluctuating symptoms over long periods of time. Patients may experience gas, bloating, dyspepsia, constipation, diarrhea, flatus, diarrhea alternating with constipation, and the passage of mucous in the stools. Crampy abdominal pain may be present.
It is the goal of physicians to assess these complex symptoms and address these complaints by performing appropriate medical tests.
Diagnosis of irritable bowel syndrome:
IBS investigators have identified a set of symptoms that provide physicians with guidelines toward a diagnosis of IBS. These are called the Rome Criteria.
The Rome criteria are:
1. Continuous or recurrent symptoms of abdominal pain or discomfort that
A) may be relieved with defecation,
B) may be associated with a change in frequency, or
C) May be associated with a change in the consistency of stools.
2. Two or more of the following are present at least 25 percent of the time:
A) Altered stool frequency (greater than 3 bowel movement per day or less than 3 bowel movements per week)
B) Altered stool form (hard or loose watery stools or poorly formed stools)
C) Passage of mucous stools
D) Bloating (feeling of abdominal distention)
Many patients experience other symptoms that are consistent with irritable bowel syndrome. However, the Rome criteria do assist researchers and clinicians by correlating and describing symptoms uniformly.
Other important factors are the presence or absence of pain at night, gastrointestinal bleeding, fevers, chills, sweats, weight loss, etc. The presence of these types of symptoms suggest alternative diagnoses. These complaints do not exclude an underlying diagnosis of irritable bowel syndrome but suggest other diagnoses that may have other treatments. Thus, IBS may be coexistent with other acute or chronic gastrointestinal illnesses.
Evaluation of IBS patients:
Patients with irritable bowel syndrome are initially evaluated with a complete history, physical and a review of their medication. Appropriate tests performed initially include:
1. CBC
2. Serum electrolytes with evaluation of BUN and creatinine
3. Erythrocyte sedimentation rate (ESR)
4. Urinalysis
5. Stool cultures for ova and parasites
6. Clostridium difficile cultures of stool
7. Fecal occult blood test evaluation
8. Stain of feces for white blood cells
9. Stains of fecal samples for fat
10. Routine cultures of stools for bacterial pathogens
11. Liver function tests
12. Rectal exam
13. Flexible sigmoidoscopy
14. Abdominal x-rays
The above evaluation will be tailored to individual patients' complaints and family histories. As an example, a patient with a family history of colon cancer or colon polyps should be evaluated with either a barium enema or colonoscopy in order to evaluate the presence or absence of these factors.
Subgroups of irritable bowel syndrome:
Patients with irritable bowel syndrome have multiple symptoms. Many patients may experience common groups of problems.
In general, most patients with irritable bowel syndrome experience complaints of dyspepsia and upper abdominal discomfort. Dyspepsia is an acid related disorder that has multiple features consisting of gastroesophageal reflux as well as other upper abdominal complaints.
A patient's bowel patterns are also used to assist physicians with the selection of appropriate treatment.
Constipation predominant irritable bowel syndrome:
Patients with constipation predominant irritable bowel syndrome should be treated with an increase in fiber. If the fiber content of their stool is increased and patients continue to experience constipation, addition of non-stimulant laxatives can be instituted. These are stool softeners, such as Colace or Surfak. Others such as milk of Magnesia or lactulose may be useful.
Diarrhea predominant IBS:
Patients with diarrhea predominant irritable bowel syndrome should have a careful dietary history taken. It is especially important that patients with this type of diarrhea avoid lactose, fructose and sorbitol. Sorbitol is commonly found in chewing gum and breath mints. Sorbitol is non-absorbable and may induce diarrhea. In addition, lactose intolerance is extremely common. A lactose hydrogen breath test may assist in the evaluation of lactose intolerance.
When patients have no specific dietary intolerances, treatment with diphenoxylate or loperamide may be appropriate. In addition, tricyclic antidepressants (TCA's) have been clearly shown to improve diarrhea and abdominal cramps. Often times, these medications (desipramine and amitryptyline) can be used in small doses at night. Tricyclic antidepressants can be increased if needed.
In patients who have continued discomfort, or sub-optimal response to tricyclic antidepressants, calcium channel blockers (Verapamil 40 mg po bid) may be used as a second line treatment.
Pain, gas, bloat predominant IBS:
Patients with this symptom complex should have mechanical obstruction of the small bowel or colon evaluated completely. This is usually accomplished by simple abdominal x-ray or barium studies. Review of a dietary history of non-absorbed carbohydrates (i.e. complex carbohydrates) is quite helpful. Therapeutic trials of antispasmodics such as Hyoscamine, Bentyl, etc. are also very useful. It is important that patients avoid gas forming foods such as legumes (i.e. vegetables containing complex carbohydrates), lactose, fructose and sorbitol.
Patients with constipation, and the above complaints, are usually not treated with tricyclic antidepressants because of the possibility of exacerbating their constipation.
Pathophysiology of irritable bowel syndrome:
Irritable bowel syndrome has been investigated extensively. Over the past several years a great deal of information regarding brain-gut interaction has evolved. A model, which includes scientific and psychological components, has been developed to evaluate patients with IBS.
Neurologic innervation of the gastrointestinal tract, associated with altered interpretation of neurologic messages from the GI tract by the central nervous system may result in the symptoms experienced by IBS patients.
Input to the CNS, from the gastrointestinal tract arrives at the hypothalamus, periaqueductal gray (PAG) area and amygdala. These centers are associated with interpretation and modulation of pain perception. Neurologic output from these areas of the central nervous system (CNS) are then returned to the gastrointestinal tract via the spinal cord. This circuit (from gut to brain and brain to gut) appears to be abnormal in patients with irritable bowel syndrome. The exact abnormalities are unclear.
Emotional stressors commonly exacerbate symptoms in IBS. How these emotional factors are processed by the central nervous system and their subsequent effects on the gastrointestinal tract is unclear. In some cases it appears that the amount of serotonin involved in transmission of neurologic impulses to the GI tract is abnormal. Thus, medications such as alosetran (Lotronex) appear to be extremely useful in these patients by modulating the amount of serotonin available. The alosetran (Lotronex) has been shown to be effective in patients with diarrhea predominant IBS. Patients report a significant reduction in the amount of diarrhea and the severity, and frequency, of their abdominal pain.
Findings negative for IBS:
1. Onset at old age
2. Increasing severity of symptoms
3. Nocturnal symptoms
4. Fever
5. Weight loss
6. Rectal bleeding
7. Fat in the stools
8. Dehydration
Initial therapy for IBS:
Constipation:
1. Fiber
2. Osmotic laxatives if needed
Diarrhea:
1. Antidiarrheals such as Loperamide and Diphenoxylate
Pain:
1. Antispasmodics
Long-term IBS therapy:
1. Daily low-dose antidepressants
A) TCAs (tricyclic antidepressants) - diarrhea predominant IBS
B) SSRIs (selective serotonin reuptake inhibitors) - in constipation predominant IBS
