What are the diagnostic criteria and treatment options for Irritable Bowel Syndrome (IBS)?

Diagnosing Irritable Bowel Syndrome (IBS)

The diagnosis of IBS should be made using the Rome IV criteria, which requires recurrent abdominal pain at least 1 day per week in the last 3 months, with symptom onset at least 6 months before diagnosis, associated with two or more of: pain related to defecation, change in stool frequency, or change in stool form. 1, 2

Diagnostic Criteria Evolution

• The Manning criteria established six key symptoms: abdominal pain relieved by defecation, looser stools with onset of pain, more frequent stools with onset of pain, abdominal distension, passage of mucus, and sensation of incomplete evacuation 1
• Rome I criteria required at least three months of recurrent symptoms of abdominal pain/discomfort relieved with defecation or associated with changes in stool frequency/consistency 1
• Rome II criteria required 12 weeks of abdominal discomfort/pain with two of three features: relieved by defecation, associated with change in stool frequency, or associated with change in stool consistency 1
• Rome IV criteria (current standard) require recurrent abdominal pain at least 1 day/week in the last 3 months, with symptom onset at least 6 months before diagnosis 1, 2

Diagnostic Approach

Initial Assessment

• Take a detailed history focusing on cardinal symptoms: abdominal pain and altered bowel habits (abnormal stool frequency and/or consistency) 1
• Confirm the relationship between pain and bowel habit changes (pain relieved or exacerbated by defecation, or associated with changes in bowel habits) 1
• Assess predominant stool pattern using the Bristol stool chart 1
• Evaluate for supportive features: bloating, visible abdominal distension 1
• Document onset and duration of symptoms, including any post-infection onset, antibiotic use, or stress/psychological trauma 1

Red Flags Requiring Further Investigation

• Weight loss, rectal bleeding, nocturnal symptoms, or anemia 1, 2
• Family history of colorectal cancer or inflammatory bowel disease 1
• Age over 45 years at symptom onset 1
• Short history of symptoms 1
• Atypical symptoms 1

Baseline Investigations

• Full blood count 1, 3
• C-reactive protein or erythrocyte sedimentation rate 1, 3
• Celiac serology 1
• Fecal calprotectin (if diarrhea and age <45 years) 1

Additional Investigations (Based on Clinical Presentation)

• Sigmoidoscopy if colonic symptoms are present 1
• Thyroid function tests, stool microscopy if diarrhea predominant 1
• Lactose tolerance testing if patient consumes substantial amounts of milk (>280 ml/day) 1
• Colonoscopy or barium enema for patients >45 years with colonic symptoms or family history of colon cancer 1

IBS Subtypes Based on Predominant Stool Pattern

• IBS with constipation (IBS-C) 2
• IBS with diarrhea (IBS-D) 2
• Mixed IBS (IBS-M) 2
• Unsubtyped IBS 2

Supportive Diagnostic Features

• Female sex 1
• Age <45 years with history >2 years 1
• History of frequent healthcare visits for non-gastrointestinal complaints 1
• Presence of extraintestinal symptoms (back pain, bladder and gynecological symptoms, insomnia) 1
• Comorbid functional disorders (fibromyalgia, tension headache, chronic fatigue) 1

Common Pitfalls in IBS Diagnosis

• Treating IBS as a diagnosis of exclusion rather than making a positive diagnosis based on symptom criteria 4
• Excessive diagnostic testing leading to increased patient anxiety 1, 5
• Failure to recognize that symptoms often fluctuate over time 2
• Not acknowledging overlap with other functional disorders 2, 6
• Missing organic diseases that can mimic IBS (celiac disease, inflammatory bowel disease, microscopic colitis) 1, 7

Prognosis

• Once a functional diagnosis is established, the incidence of new non-functional diagnoses is extremely low 1, 2
• Persistence of symptoms is expected and does not justify suspicion of other diagnoses 5
• Only changes in the clinical pattern over time justify additional investigations 5