Irritable bowel syndrome (IBS) is diagnosed from the symptom pattern after organic disease has been excluded, and its management is stepped: diet and lifestyle first, then drugs chosen for the predominant symptom, and psychological therapy when symptoms remain refractory.
Physical examination
Physical examination is mostly normal in IBS. In some cases deep palpation of the colon reveals abdominal tenderness, but there are no specific physical signs, and the examination is used mainly to look for an alternative explanation.
Diagnosis
Diagnosis begins with the symptom pattern and a search for alarm features. Alarm features, or red flags, in a patient with an IBS-like picture mean that organic disease must be looked for rather than assumed away:
- a history of gastrointestinal bleeding
- unexplained weight loss
- unexplained vomiting
- progressive dysphagia
- inflammatory bowel disease (IBD)
- coeliac disease
- a family history of malignancy
- anaemia
- new-onset symptoms in older age
The conditions most often weighed in the differential diagnosis are intestinal parasitosis, IBD, food intolerance, small intestinal bacterial overgrowth (SIBO) and colorectal neoplasm.
IBS is recognised from the Rome IV symptom pattern (see Clinical Features and Diagnostic Criteria of IBS), and a positive diagnosis is preferred over exhaustive exclusion. Testing is still used to rule out the organic diseases that can mimic IBS; the usual tests are:
- full blood count
- CRP and ESR (C-reactive protein and erythrocyte sedimentation rate, both inflammatory markers)
- coeliac serology
- faecal calprotectin, when diarrhoea is present
- colonoscopy in patients with the alarm features listed above
Breath testing for SIBO is not routinely recommended, because its role in IBS is uncertain.
Treatment
Management is guided by the predominant symptom, but it always begins with a firm positive diagnosis, an explanation that IBS is chronic and not dangerous, and general measures. Drugs are added according to the symptom, and psychological therapy is reserved for symptoms that remain refractory.
Diet and lifestyle. Regular meals, adequate fluid, and limits on caffeine, alcohol and fizzy drinks may help. Fibre is adjusted rather than simply increased: insoluble fibre such as bran often worsens symptoms and is discouraged, while soluble fibre such as ispaghula or psyllium is better tolerated. When symptoms persist, a low FODMAP diet — a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols — should be supervised by a healthcare professional with expertise in dietary management. Probiotics may be tried for at least 4 weeks while the effect is monitored.
Drugs are chosen for the predominant symptom:
- for pain and bloating, antispasmodics taken as required;
- for constipation, laxatives, avoiding lactulose because it worsens bloating, and — if laxatives fail and constipation has lasted at least 12 months — the secretagogue linaclotide;
- for diarrhoea, loperamide as the first-choice antimotility agent;
- for IBS with diarrhoea that does not settle, rifaximin, a non-absorbable antibiotic;
- for pain that persists despite these measures, a low-dose tricyclic antidepressant such as amitriptyline, started at 5–10 mg at night and usually not increased beyond 30 mg; an SSRI is considered if a tricyclic is ineffective.
Psychological therapy. When symptoms do not respond to drug treatment after 12 months and a continuing symptom profile develops (refractory IBS), referral for cognitive behavioural therapy, gut-directed hypnotherapy or another psychological therapy is considered.