IRRITABLE BOWEL SYNDROME (IBS)

Dr. Mohamed Shekhani MBChB-CABM-FRCP

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IBS: Epidemiology

A common disorder, with a 7% prevalence .

Women are 1.5 times more likely to be affected than men, most commonly between ages 20-40 years.

Onset after the age of 50 years is uncommon.

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IBS:Pathophysiology

Not well understood,may vary depending on the subtype& include: Abnormal GIT motility Visceral afferent hypersensitivity Autonomic innervation abnormalities. Altered mucosal immune system activation may occur, particularly in patients with diarrhea who develop symptoms after an acute gastroenteritis (postinfectious IBS). Depression, anxiety, a H/O sexual abuse, phobias, somatization are commonly associated, but not psychosocial factors. Health-related quality of life (HRQOL) scores are lower in IBS than in unaffected persons, but ? Cause or effect. IBS patients who seek evaluation& treatment are more likely to have comorbid psychiatric illness& psychological stress is likely to exacerbate symptoms.

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IBS:burden

IBS is costly, with direct& indirect (including decreased work productivity) costs estimated at $20 billion, with IBS patients consuming > 50% more in health care resources than matched controls. Increased health care utilization in IBS patients is directly related to somatization levels.

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IBD: Diagnosis

Based solely on clinical grounds. As no biochemical, radiographic, endoscopic or histologic marker exists, the dignosis depends on Rome criteria. Now depends on Rome 3, but only Rome I criteria have been evaluated for accuracy, with a sensitivity of 71% & specificity of 85%. The ACG task force on IBS has recommended a simpler definition: Abd pain associated with altered bowel habits (change in stool form or frequency) over a period of at least 3 months.

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Diagnosis: Rome 3

Recurrent abd pain or discomfort (abn sensation not described as pain) at least 3 days a month in past 3 months (with onset > 6 months prior) associated with two or more of the following: Improvement with defecation Onset associated with change in frequency of stool Onset associated with change in form (appearance) of stool Absence of alarm indicators that suggest other diseases: Age >50 years Male Short history of symptoms Documented weight loss Nocturnal symptoms Family history of colon cancer Rectal bleeding Recent antibiotic use

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IBD: Diagnosis

Rome III criteria describes 4 subtypes of IBS: Constipation-predominant Diarrhea-predominant Mixed Unsubtyped. Supportive symptoms may include: Abnormal stool frequency (>3/d, <3ds/week) Abnormal stool form (lumpy/hard or loose/watery) Straining or urgency or a sensation of incomplete evacuation, mucus Bloating.

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IBS: Diagnosis

Meeting the diagnostic Rome criteria for IBS& the absence of alarm symptoms& signs regarded as reassuring that the patient does not have organic disease such as IBD, CRC or celiac disease. Recent review of the literature has suggested that nocturnal symptoms as well as rectal bleeding in particular are not helpful in separating IBS from patients with organic disease. While other alarm criteria such as anemia& weight loss lack sensitivity for the diagnosis of organic disease, they are specific. Affected patients may describe non GIT somatic symptoms such as headache, urinary symptoms, backache, and fatigue.

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IBS: Evaluation

Patients with potential IBS should not undergo a potentially expensive or harmful evaluation that may undermine their confidence in the diagnosis& in the physician. Anemia is an alarm sign; a complete blood count should be performed after the onset of symptoms. Patients with IBS with diarrhea & mixed IBS should have serologic tests for celiac disease, which occurs more commonly in patients with these IBS subtypes than in the general population. A possible link between IBS& small intestine bacterial overgrowth, but ACG not recommend routine testing. Testing for lactose intolerance, more common among IBS, should be conducted only if this diagnosis is unclear on clinical grounds.

Colonoscopy is indicated only if patients are > 50 years.

In any patient with alarm features, further evaluation is mandated& should be tailored to symptoms; i.e patients with constipation need imaging to rule out a mechanical obstruction. In patients with IBS with diarrhea who undergo colonoscopy, biopsies of the colon should be done to evaluate for microscopic colitis, particularly if there is suggestion of a secretory diarrhea.

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IBS: treatmet

Depends on a patients predominant symptoms. Although patients often link diet to symptoms, no clear data support elimination diets or food allergy testing, but if individual patients identify clear food triggers, these can be eliminated or reduced.

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IBS: treatmet for CP-IBS

Bulking agents, specially fiber in the form of psyllium hydrophilic mucilloid (ispaghula husk) & calcium polycarbophil, may improve global IBS symptoms but can be associated with bloating & flatulence.

Laxatives appear to be effective in chronic constipation; although laxatives appear to improve frequency of bowel movements in those with constipation, it remains unclear whether they have any effect on pain. Osmotic laxatives such as milk of magnesia as well as nonabsorbable polyethylene glycol, sorbitol,lactulose are generally believed to be safer than stimulant laxatives, but they may be associated with bloating / flatulence; so senna / bisacodyl may be appropriate for intermittent use for constipated patients.

Tegaserod, a 5-HT4 (serotonin) agonist had been previously approved to treat IBS with constipation in women& improved bowel movements, abdominal pain& global IBS symptoms. Lubiprostone is a chloride channel antagonist approved to treat chronic constipation in adults, but it does not alleviate abd pain.

IBS: treatmet for CP-IBS

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IBS: treatmet for DP-IBS

In IBS with diarrhea, loperamide improved both bowel movement frequency & consistency,but it had no effect on other IBS symptoms. Alosetron, a 5-HT3 antagonist, alleviates abdominal pain, global IBS symptoms, and diarrhea and urgency in women and men with IBS with diarrhea; potential serious but uncommon side effects include both severe constipation & ischemic colitis. It should be reserved for patients who have failed to respond to conventional therapies.

IBS: treatmet for DP-IBS

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IBS: treatmet for abd pain

Antispasmodic agents, including Mebeverine,dicyclomine, hyo scyamine, peppermint oil, function as GIT smooth muscle relaxants. Reduce abd pain in the short term, but not well substantiated, associated with side effects that preclude their use& may cause constipation. Tricyclic antidepressants &SSRI have analgesic properties; tricyclics also have an anticholinergic effect & may induce constipation. Smaller doses than are used in the treatment of depression are generally recommended. Comorbid depression may best be treated with a SSRI. Psychosocial stressors should also be addressed.

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IBS: Bacterial overgrowth trt

While the link between small intestinal bacterial overgrowth & IBS remains unclear, the short-term (10-14 days) use of the nonabsorbed antibiotic rifaximin at doses between 1000-1200 mg/day has demonstrated improvement in global IBS symptoms, bloating &diarrhea in IBS&diarrhea. Other antibiotics such as neomycin may be effective. The efficacy of probiotics is yet to be determined adequately. Antibiotic /probiotic therapy has been used because bacterial overgrowth has been implicated, possibly through abnormal motility or as a sequela of postinfectious IBS. Rifaximin has been effective in relieving symptoms in patients with bacterial overgrowth. Bifidobacterium infantis is the only probiotic that has proven efficacy in the treatment of IBS.