Gastroenterology · Functional Gastrointestinal Disorders
The facts most likely to be tested
Diagnosis of Irritable Bowel Syndrome (IBS) is based on the Rome IV criteria, requiring recurrent abdominal pain at least one day per week for the last three months, associated with two or more of the following: defecation, a change in stool frequency, or a change in stool form.
IBS is a diagnosis of exclusion; clinicians must rule out alarm symptoms such as unintentional weight loss, nocturnal diarrhea, rectal bleeding, iron deficiency anemia, or a family history of inflammatory bowel disease or colorectal cancer.
The Bristol Stool Form Scale is used to classify IBS subtypes into IBS-D (diarrhea-predominant), IBS-C (constipation-predominant), IBS-M (mixed), or IBS-U (unclassified).
First-line management for all IBS patients involves lifestyle modifications, specifically a low-FODMAP diet and increased soluble fiber intake.
IBS-D is pharmacologically managed with loperamide for acute symptom control or eluxadoline (a mu-opioid receptor agonist) for chronic maintenance.
IBS-C is managed with osmotic laxatives like polyethylene glycol or secretagogues such as linaclotide or lubiprostone.
Tricyclic antidepressants (TCAs) are the preferred pharmacological intervention for patients with refractory abdominal pain due to their effect on visceral hypersensitivity.
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A 28-year-old female presents with a 6-month history of recurrent abdominal pain that improves after defecation. She reports that her stools are often hard and lumpy, occurring only twice a week. She denies nocturnal diarrhea, hematochezia, weight loss, or fever. Physical examination reveals mild lower abdominal tenderness without guarding or rebound. Laboratory studies, including a complete blood count and tissue transglutaminase IgA, are within normal limits.
What is the most appropriate initial management for this patient?
Lifestyle modifications and increased soluble fiber intake
The patient meets Rome IV criteria for IBS-C without alarm symptoms, making it a diagnosis of exclusion; initial management focuses on conservative measures like dietary changes and fiber supplementation.
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High yield triage
Etiology / Epidemiology
Functional disorder of the GI tract; younger females are most commonly affected.
Clinical Manifestations
Chronic abdominal pain associated with defecation or change in stool frequency/form.
Diagnosis
Rome IV criteria requires symptoms for at least 6 months.
Treatment
Lifestyle modification and dietary changes (low FODMAP) are first-line.
Prognosis
Chronic, relapsing course; no increased risk of malignancy or mortality.
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Epidemiology & Etiology
IBS is a common functional bowel disorder with a higher prevalence in females and patients <50 years old. It is often triggered by post-infectious states or psychological stressors. There is no structural or biochemical abnormality identified on routine testing.
Pertinent Anatomy
The disorder involves the entire GI tract, specifically the enteric nervous system and the gut-brain axis. Dysregulation of the visceral afferent nerves leads to heightened sensitivity to normal luminal distension.
Pathophysiology
Pathophysiology involves visceral hypersensitivity and altered GI motility. Patients exhibit abnormal brain-gut axis signaling, leading to exaggerated responses to stress. Alterations in the gut microbiome and low-grade mucosal inflammation may also contribute to symptom severity.
Clinical Manifestations
Patients present with abdominal pain relieved by defecation and changes in stool frequency or appearance. Red flag symptoms requiring further workup include weight loss, nocturnal diarrhea, rectal bleeding, and onset after age 50. The condition is characterized by Rome IV criteria, which emphasize the relationship between pain and bowel habits.
Diagnosis
Diagnosis is clinical using the Rome IV criteria: recurrent abdominal pain at least 1 day/week for 3 months, associated with two or more of: related to defecation, change in frequency, or change in form. No gold standard test exists; diagnosis is one of exclusion. Routine colonoscopy is not indicated in young patients without alarm features.
Treatment
Initial management focuses on lifestyle modification and low FODMAP diet. For IBS-C, polyethylene glycol is the first-line osmotic laxative. For IBS-D, loperamide is the preferred agent. Avoid chronic opioid use due to risk of dependence and worsening constipation.
Prognosis
IBS is a chronic, relapsing condition with no increased risk of colorectal cancer or inflammatory bowel disease. Management focuses on symptom control and improving quality of life. Patients should be reassured that the condition is benign.
Differential Diagnosis
Celiac disease: positive serology (tTG-IgA)
Inflammatory Bowel Disease: elevated fecal calprotectin
Microscopic colitis: chronic watery diarrhea in older adults
Lactose intolerance: symptoms triggered specifically by dairy
Colon cancer: weight loss and iron deficiency anemia