Introduction:
Irritable Bowel Syndrome (IBS) is probably the most common and least understood disorder a general physician encounters in clinical practice. It was used by some physicians to connote any gastrointestinal symptom where there is no demonstrable cause found. It gained the unfortunate reputation of being a wastebasket diagnosis when a diagnosis is not positively identified. Many physicians, on the other hand, did not consider IBS as a disease but is viewed as nothing other than a somatic manifestation of a psychological stress. Synonymous names used sometimes are spastic colon or mucous colitis.

Epidemiology:
Symptoms of IBS affects one in every six Americans with comparable prevalence in other western countries. It is two to three times more common in women than in men. Women also constitute more than 80% of severe cases. It is equally prevalent in white as as in blacks. One third of patients consult a physician. The first presentation is usually between age 30 to 50. IBS accounts for about 12% of Primary Care Physician visits and more than half of the referrals to Gastroenerologists.

Diagnostic Criteria:
The most common criteria is Rome Criteria which is a clinical one. According to this criteria IBS is considered the diagnosis if there is:
1. Abdominal pain or discomfort relieved by defecation or associated with changes in frequency or consistency of stool for at least three months, and/or
2. An irregular pattern of defecation in at least 25% of time with three or more of the following: altered stool frequency, altered stool form (hard, loose or watery), altered stool passage (urgency or straining, feeling of incomplete evacuation), passage of mucous, bloating or feeling of abdominal distention.

Pathophysiology:
Pathogenesis of IBS is poorly understood. It seems that various roles are played:
1. Abnormal Motor Function: IBS is associated with a generalized disorder of smooth muscles of bowels. There is abnormal response of colon to meals, drugs, gut hormones and stress. Gastrocolic response after meals is augmented. Increased fasting colonic contraction and rapid transit in the proximal colon has been linked to diarrhea while reduction in high amplitude propagated contractions in the left colon has been associated with constipation.
2. Disturbed Sensation: Abnormal perception of gut sensation (visceral hypersensitivity) is a characteristic finding in IBS.
3. Central Nervous System: The role of CNS is strongly suggested by (1) the clinical association of emotional disorders and stress with symptoms exacerbation (2) the therapeutic response to therapies that act on cerebral cortical sites. Abnormal psychiatric features are associated with more than 40-56% of IBS patients in tertiary referral centers. Coexisting psychiatric disease including depression, panic disorder or history of sexual or physical abuse has been associated. In primary care settings the prevalence of psychiatric disorders are less than in tertiary settings. Stressful life events, personality, level of social support and childhood experience influence how a patient responds to a chronic illness such as IBS.
4. Dietary Intolerance & Food Allergies: Lactose intolerance may coexist with IBS. Excessive intake of sorbitol or fructose may induce diarrhea and bloating. True food allergies are probably rare and difficult to diagnose since results of skin tests and immunological testing for possible food allergies has been equivocal. Dietary exclusion of possible offending diet should be done.
5. Infection: 20% of IBS patients have history of traveler's diarrhea or gastroenteritis preceding the onset of IBS symptoms.

Clinical Features:
Symptoms:
Abdominal Pain: Cramp like or aching occurring in episodes located in hypogastrium (25%), right side (20%), left side (20%) and epigastrium (10%). The pain is relieved by defecation and is associated with change in frequency or consistency of stool. Pain occurs during waking hours only.
Altered Bowel Habits: This is the most consistent feature of IBS. The most common pattern is constipation alternating with diarrhea. Some patients have constipation as a predominant symptom with a stool that is hard and narrow in caliber or pellet-like. These patients have symptoms of incomplete evacuation leading to repeated attempts at defecation. These patients may have weeks or months of constipation interrupted by brief periods of diarrhea. Other patients have diarrhea as the predominant symptom with frequent small volume of loose stool aggravated by emotional stress or eating. Stools may be accompanied by excessive amount of mucous.
Abdominal Bloating: Patients with IBS usually complain of excessive bloating and flatulence.
Upper GI Symptoms: Some patients with IBS complain of dyspepsia, heartburn and nausea.
Signs: Usually absent, may have some abdominal tenderness.

Diagnosis:
Since IBS is a disorder where there is no pathognomonic feature, its diagnosis relies on recognition of positive clinical features and elimination of other organic diseases. Careful history and physical examination should be done. Exhaustive testing before making the diagnosis of IBS as a diagnosis of exclusion should be discouraged. CBC, multichemistry, stool ova, parasites & blood and sigmodoscopy (patient over 50 should have a colonoscopy) should be done.

Factors to be considered when determining the aggressiveness of the diagnostic evaluation include the duration of symptoms, the change of symptoms over time, age and sex of patient, prior diagnostic studies, family history of colorectal cancer and the degree of psychosocial dysfunction. Other tests depend on presentation considering the aforementioned factors.

Clinical features suggesting IBS include the following (see also Rome criteria): recurrence of lower abdominal pain with altered bowel habits over a period of time without progressive deterioration, onset of symptoms during periods of stress and emotional upset, and absence of other symptoms such as fever, weight loss, anemia or blood in stool.

Differential Diagnosis:
Inflammatory Bowel Disease and colorectal cancer: With diarrhea as the predominant symptom: Lactose intolerance, hyperthyroidism, sprue, giardiasis, intestinal bacterial overgrowth, laxative abuse and carcinoid syndrome.

With patients who have constipation as the predominant symptom: Intestinal malignancy, dyschesia, Hirschsprung disease, hypothyroidism and hypercalcemia.

Treatment:

Patient counseling and education:
A good physician-patient relationship is therapeutic in IBS. Reassurance and explanation is an essential component of the management. It is important to explain to the patient the pathogenesis of the disorder and how the diagnosis is made and that he/she is not under tested. It is important to tell the patient that the symptoms are real and that the disorder is not a life threatening disorder and that it does not lead to malignancy. Symptoms may be lifelong but they tend to come and go.

Diet Modifications:
Increase dietary fibers to at least 30 g daily, avoid milk products (Lactose intolerance may occur at same time as IBS), avoid foods like cabbage, cauliflower, beans and onion since their galactose content is fermented in the large bowel producing excessive amount of gas, and avoid a high fat diet.

Activity:
Exercise may help patients with constipation since low physical activity has been reported to be associated with constipation.

Pharmacotherapy:
This should be reserved for patients who do not respond to reassurance and conservative therapy. It is also important before considering drug therapy to note that the placebo response of patients with IBS is 40-70%. Drug therapy depends on predominant symptoms: 1. abdominal pain: anticholinergics (L-Hyoscyamine, dicyclomine) or antichlonergic/anxiolytic combination, 2. diarrhea: loperamide or diphenoxylate with atropine, and 3. constipation: bulk laxatives and occasional stool softeners.

Other drugs are tricyclic antidepressants. Possible future drugs are Kappa opioid compounds and serotonin receptor (5HT3) antagonists such as alosteron and octreotide.

Other treatment:
Some cases may benefit from psychotherapy, behavioral modifications, biofeedback or hypnotherapy.

Conclusion:
Even with the recent advances in the knowledge of IBS, it is still a poorly understood disorder. Patient reassurance and education about the disease are of paramount importance. The patient should know that the disease is real but is not a serious one. The physician in turn should understand the impact of IBS on the quality of life of IBS patients. Continuing supervision and encouragement, reassurance and support through periodic office visits help the patient develop confidence in the care provided. The physician must also be alert that patients with IBS are vulnerable to organic diseases developing at any time in the future.

References
Owyau C. Chapter 288, Harrison's Principles of Internal Medicine, 15th Edition Volume 2 McGraw-Hill 2001.
Thompson W, Heaton KW. Irritable bowel syndrome in general practice: prevalence, characteristics, and referral, Smyth HT, Smyth C. Gut 2000:46 (1): 7-8.
Camelleri M. Management of the irritable bowel syndrome. Gastroenterology 2001:120(3): 652-68.
Zar S, Kumar D, Benson MJ. Food hypersensitivity and irritable bowel syndrome Alimont Pharmacy Ther 2001:15(4): 439-49.
Talley NJ. Chapter 131, Cecil Textbook of Medicine, 21st Edition, W.B. Saunders, 2000.
Rothestein RD. Irritable bowel syndrome Med Clin Nort Am 2000:84(5): 1247-57.
Tynes L, Gibson, FL. Irritable bowel syndrome: Overview of the diagnosis and treatment. La State Med Soc 1999:(2); 76-81.
Sutton, FM. Chapter 83, Saunder's Manual of Medical Practice, W.B. Saunders Company 1996.
Shea B, Soffer E. The challenge of irritable bowel syndrome: creating an alliance between patient and physician. Clev Clin J Med 2001:68(3); 224-5, 229-33, 236-7.
Rothstein, RI. Chapter 50, Textbook of Primary Care Medicine, Second Edition, Mosby 1996.
Mayer EA, Naliboff ED, Change L, Coutinho SV. Stress and irritable bowel syndrome. AM J Physical Gastrointest Liver Physical 2001:280(4);G519-24.
Schmulson MW, Change L. Diagnostic approach to patients with irritable bowel syndrome. Am J Med:107(5A);205-268.
Hammer J, Talley NJ. Diagnostic criteria for irritable bowel syndrome. AM J Med:8.107(5A);58-118. Camilleri M. Motor function in irritable bowel syndrome. Can J Gastroentrol 1999:suppl A:RA-11A.

* * * *

About the Author
Nosshey F. Hanna, M. D. is an Associate Professor of the American College of General Medicine.

This article represents the opinion of the Author and does not reflect the official policy of the American Academy of General Physicians nor the institutions with which the Author is affiliated.