Definition
A.Irritable bowel syndrome (IBS) is the most common of the gastrointestinal (GI) motility disorders. IBS is responsible for significant direct and indirect healthcare costs. It is a chronic relapsing functional disturbance of intestinal motility marked by a common symptom complex that includes bloating and abdominal pain or discomfort associated with defecation.
B.Bladder dysfunction has been identified in 50% of patients with IBS. Patients commonly transition between subgroups.
C.According to the Rome III criteria, IBS is the presence of recurrent abdominal pain or discomfort at least 3 days/month that occurs in association with altered bowel habits over a period of at least 3 months.
D.IBS is defined by symptom-based diagnostic criteria, in the absence of detectable organic causes. Rome III criteria for IBS is related to stool characteristics:
1.IBS with diarrhea predominant (IBS-D): Loose stools (small volume, pasty/mushy or watery) more than 25% of the time and hard stools less than 25% of the time.
2.IBS with constipation (small, hard, pelletlike stools) predominant (IBS-C): Hard stools more than 25% of the time and loose stools less than 25% of the time.
3.IBS with alternating bouts of constipation and diarrhea, mixed or cyclic pattern (IBS-M): Both hard and soft stools more than 25% of the time.
E.On clinical grounds, other subclassifications are used:
1.Based on symptoms:
a.IBS with predominant bowel dysfunction.
b.IBS with predominant pain.
c.IBS with predominant bloating.
2.Based on precipitating factors:
a.Postinfectious (PI-IBS).
b.Food-induced (meal-induced).
c.Stress-related.
Incidence
A.IBS is common, accounting for about 50% of GI complaints seen by healthcare professionals, and is a major cause of morbidity in the United States. Studies suggest nearly 20% of all adults suffer from some form of the condition; however, only a fraction seek medical help. IBS is recognized in children; symptoms consistent with IBS are reported in 16% of students age 11 to 17 years. IBS is not described in preschool-aged children.
B.IBS with diarrhea is more common in men.
C.IBS with constipation is more common in women.
D.The American College of Gastroenterology (ACG) has recognized IBS as a key component of Gulf War syndrome.
Pathogenesis
A.IBS has an absence of detectable pathology, and laboratory tests are unrevealing. The understanding of IBS has evolved from a disturbance in bowel motor activity to a more integrated understanding of visceral hypersensitivity and brain–gut interaction. It is thought to be both a normal response to severe stress and a learned visceral response to stress:
1.Nonpropulsive colonic contractions lead to IBS-C predominant.
2.Increased contraction in the small bowel and proximal colon with diminished activity in the distal colon lead to IBS-D predominant.
3.Most patients with functional disorders appear to have inappropriate perception of physiologic events and altered reflex responses in different gut regions.
4.The brain–gut transmitters act at different sites in the brain and gut and lead to varied effects on GI motility, pain control, emotional behavior, and immunity. Serotonin plays a critical role in the regulation of GI motility, secretion, and sensation. Studies have shown that IBS may be related to an imbalance in mucosal serotonin and 5-HT availability caused by defects in 5-HT production, serotonin receptors, or serotonin transport.
Predisposing Factors
A.Age:
1.IBS mainly occurs between the ages of 15 and 65 years:
a.50% of IBS occurs prior to age 35.
b.40% of IBS occurs between ages 35 and 50.
B.Gender:
1.Women are two to three times more likely to have IBS.
C.Emotional factors and situational stress.
D.Prior GI infection–induced IBS.
E.Genetics is considered a factor.
F.Carbohydrate intolerance may produce significant symptoms.
Common Complaints
A.Chronic relapsing stool pattern:
1.Diarrhea, over three loose stools per day, or
2.Alternation of diarrhea with constipation. Diarrhea is typically small in volume, has visible mucus, and may follow a hard movement by a few hours, or
3.Constipation: Less than three bowel movements (BMs) per week.
B.Feeling of incomplete evacuation.
C.Abdominal distension and bloating.
D.Straining with BMs.
E.Aching or cramps in periumbilical or lower abdominal region.
F.Pain relief with BM.
Other Signs and Symptoms
A.Change in bowel function.
B.Clear mucous stool.
C.Pain may be precipitated by meals.
D.Pain radiates to left chest or arm, from gas in splenic flexure. Nocturnal pain is unusual and is considered a warning sign.
E.Flatulence.
F.Nausea.
G.Anxiety.
H.Depression.
I.Preoccupation with bowel symptoms.
J.Extraintestinal symptoms:
1.Dysmenorrhea.
2.Urinary frequency, urgency, and incomplete bladder emptying.
3.Impaired sexual function and dyspareunia.
4.Fibromyalgia.
K.Menses may exacerbate IBS symptoms.
Subjective Data
A.Review pattern of main symptoms, including onset, duration, and usual course.
B.Ask the patient what are the predominant symptoms—abdominal pain, diarrhea, or constipation.
C.Review the patient’s history for stress factors, and ask if recurrent symptoms occur in relation to them.
D.Ask what other symptoms occur with the pain, diarrhea, or constipation, such as bloating, blood in stool, or nighttime BMs. Bleeding, weight loss, and nocturnal diarrhea are not characteristic of IBS. IBS symptoms disappear during sleep.
E.Establish patient’s normal weight history, and determine amount of weight loss, if any, over what time period.
F.Review the patient’s diet, including the following:
1.Response to milk or lactose products.
2.Artificial sweeteners.
3.Alcohol intake.
4.Irregular or inadequate meals.
5.Insufficient fluid intake.
6.Excessive fiber intake.
7.Obsession with dietary hygiene.
8.Response to gluten (wheat, barley, rye) ingestion.
G.Inquire about the patient’s prescription, herbal, and over-the-counter (OTC) medications. Ask specifically about the use of laxatives.
H.Review travel and food history for dominant history of diarrhea.
I.Ask the patient if there is a family history of colon cancer, ulcerative colitis (UC), Crohn’s disease (CD), or malabsorption.
J.Is there any fever accompanying lower abdominal pain?
K.What is the relation of symptoms to menstruation?
Physical Examination
A.Check temperature (if indicated), pulse, respirations, blood pressure (BP). Measure height and weight to calculate a body mass index (BMI).
B.Inspect:
1.Observe general appearance. Does the patient appear anxious or depressed?
2.Inspect abdominal contour for masses and bulges.
C.Auscultate all quadrants of the abdomen for bowel sounds; note whether they are normal or mildly hyperactive.
D.Percuss the abdomen for tympany or dullness.
E.Palpate the abdomen:
1.Evaluate the abdomen for mild tenderness, rigidity, guarding, and masses.
2.Evaluate for hepatosplenomegaly.
3.Evaluate for lymphadenopathy.
F.Rectal exam:
1.Check for masses and tenderness.
2.Obtain stool for diagnostic tests.
3.Rectal exam is normal with IBS.
Diagnostic Tests
A.The ACG Task Force on IBS recommends that patients younger than 50 years of age who do not have alarm features need not undergo routine colonic imaging. Patients with IBS symptoms who have alarm features, such as anemia or weight loss, or those who are older than 60 years of age, should undergo colonic imaging to exclude organic disease.
B.Diagnosis of IBS is usually suspected on the basis of the patient’s history and physical examination without additional tests (see Table 14.20).
C.Diagnostic tests are performed to exclude organic disease that may masquerade as IBS:
1.Complete blood count (CBC).
2.Sedimentation rate or C-reactive protein (CRP).
3.Serum potassium, if the patient is on diuretics; hypokalemia may reduce bowel contractility and produce an ileus.
4.Blood glucose, if diarrhea predominates; rule out diabetes mellitus, which may present as diarrhea due to diabetic gastroenteropathy.
5.Thyroid function study.
6.Stool specimen: Culture for leukocytes and fat, ova and parasites, and occult blood. Leukocyte-free mucus is a hallmark of IBS.
7.Stool cultures for Clostridioides difficile toxin assay, if clinically indicated.
8.Barium enema (BE) and/or proctosigmoidoscopy for severe signs and symptoms, after consultation or referral.
9.Celiac serology, if appropriate.
10.Mucosal biopsy is appropriate if a colonoscopy or sigmoidoscopy is performed.
11.Esophagogastroduodenoscopy (EGD) and distal duodenal biopsy in patients with diarrhea should be considered to rule out celiac disease, tropical sprue, giardiasis, and for patients in whom abdominal pain and discomfort is located more in the upper abdomen
12.Hydrogen breath test to evaluate lactose intolerance and small-intestinal bowel overgrowth (SIBO).
Differential Diagnoses
A.IBS.
B.Refer to Table 14.20 for common and red-flag differential diagnoses for IBS:
1.Inflammatory bowel disease (IBD):
a.CD.
b.UC.
2.Viral or bacterial gastroenteritis or acute diarrhea due to protozoa or bacteria.
3.Diverticulitis.
4.GI neoplasm.
5.Medications:
a.Laxative abuse.
b.Drug(s) side effects.
C.Lactose insufficiency/deficiency.
D.Diabetes.
E.Celiac spruce/gluten etiology.
F.Endometriosis/Pelvic inflammatory disease (PID).
G.Zollinger–Ellison syndrome.
Plan
A.General interventions:
1.Advise the patient to keep a diary of events of BMs and precipitating factors. A BM record is available at www.nhsggc.org.uk/media/241191/nhsggc-bristol-stool-chart.pdf.
2.Encourage the patient to quit smoking because nicotine may aggravate symptoms.
3.Recommend daily exercise to reduce stress.
4.Stress management should be encouraged, including counseling, tapes, meditation, and yoga.
B. 
See Section III: Patient Teaching Guide Irritable Bowel Syndrome.
C.Dietary management:
1.Encourage lifestyle changes and dietary modification first. Prescribe a high-fiber diet.
2.Tell the patient to avoid foods that aggravate the bowel. Avoid gas-producing foods, such as broccoli, beans, onions, garlic, and so forth. Advise to follow a low FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols) diet. See Appendix B for the FODMAP diet. When diarrhea predominates, dietary review is essential for clues of intolerance to lactose or sorbitol.
D.Pharmaceutical therapy:
1.Advise the patient to stop all nonessential medications that may affect bowel function, especially irritant laxatives. Avoid narcotics, depressants, and other long-term drug use if possible.