Irritable Bowel Syndrome (IBS)
(Gastroenterology 2006;130:1480-91 & 2002;123:2105-07 & 2108-31)
DEFINITION:
A group of functional bowel disorders which abdominal discomfort or pain is associated with defecation or change in bowel habits, and with features of disordered defecation; As of now, no specific discriminatory findings or diagnostic tests for IBS
Subtypes: Constipation predominant, Diarrhea predominant, Alternating between constipation and diarrhea
Hallmark symptoms (not otherwise explained by other structural or biochemical abnormalities):
Lower abdominal pain/discomfort
Altered bowel function (urgency, altered stool consistency or frequency, incomplete evaluation)
Bloating
Disease severity (less than 5% considered Severe)
Clinical
Mild
Moderate
Severe
Constant symptoms
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Healthcare use
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Illness behavior
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Psychiatric diagnosis
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Chronic continuous diarrhea in the absence of pain is not IBS, although it may be functional in nature
EPIDEMIOLOGY:
Up to 20% of U.S. population reports symptoms of IBS; Most common GI diagnosis; Affects predominantly women (˜70%)
Fewer than 25% seek medical evaluation and treatment for their symptoms
IBS patients are more likely to see other physicians frequently or undergo surgery than non-IBS patients
Economic impact: 2 billion in direct healthcare costs per year and 20 billion in indirect costs (loss of work & school)
ETIOLOGIES:
The effect of stress on gut function is universal, and patients with IBS appear to have greater reactivity to stress compared to healthy patients
In other words, IBS patients appear to have lower visceral pain threshold
Differential diagnosis:
Malabsorption (celiac, postgastrectomy, pancreatic insufficiency); Dietary factors (lactose intolerance, caffeine/alcohol, fatty foods)
Infection/bacterial overgrowth (bacterial/campylobacter, parasites/giardia); IBD; Psychological (panic disorder, depression, somatization)
Gynecological disorders (endometriosis); Other (GI endocrine tumors, HIV-associated infections)
Bloating differential diagnosis:
Lactose intake, carbonated drinks, bulking agents (Metamucil), bacterial overgrowth, constipation
PATHOPHYSIOLOGY:
Evolution of thought process (1950’s to 2000’s)
Abnormal gut motility » Visceral hypersensitivity » Brain-gut interaction » 5HT mediated sensitivity
Enteric Nervous System, like CNS, has integrated circuits for program library, feedback, reflexes, information processing
Disregulation of CNS-ENS interaction: visceral hypersensitivy and abnormal colonic motility (hallmarks of functional GI disorders)
Serotonin (5HT – neurotransmitter in both gut/brain at every level) has role in mediating visceral hypersensitivity and the peristaltic reflex
95% of 5HT is found in gut, with 90% localized within enterochromaffin cells of the mucosa
IBS patients have higher post-prandial levels and they remain higher for longer periods of time
Post-infectious: IBS may be a shift in host-gut microbial relationships: ? if IBS leads to gastroenteritis, or gastroenteritis leads to IBS
IBS patients may develop symptoms after an acute episode of bacterial gastroenteritis
IBS, on the other hand, may predispose patients to bacterial gastroenteritisRelated posts:
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