Irritable bowel syndrome

Definition

Irritable bowel syndrome (IBS) is characterized by recurrent abdominal pain associated with at least two of the following features: relation to defecation, change in stool frequency or change in stool consistency. It is a disorder of gut-brain interaction (previously called a functional gastrointestinal disorder). No anatomic cause is found on laboratory tests, imaging or biopsies. The diagnosis is clinical.

Classification

By the predominant bowel habit, the following are distinguished:

• Constipation-predominant IBS (IBS-C): less frequent stools, hard or lumpy consistency
• Diarrhea-predominant IBS (IBS-D): more frequent, loose stools
• Mixed or alternating IBS (IBS-M): alternation between constipation and diarrhea

In most patients the bowel pattern is relatively consistent, but alternation is not unusual.

Occurrence & epidemiology

Irritable bowel syndrome usually begins in adolescence and early adulthood. Prevalence is highest in women aged 20 to 40 years, but in some populations it also occurs frequently in men aged 16 to 30 and in middle-aged adults. IBS is present in about 25% of people with postural orthostatic tachycardia syndrome (POTS).

Aetiopathogenesis

The cause is unknown and the pathophysiology only partly understood. IBS is now regarded as an interplay of physiologic and psychosocial factors; established risk factors are enteric infections, psychological comorbidities, female sex and age under 40 years. Emotional factors, diet, viral illness or hormones can precipitate or aggravate symptoms.

Physiologic factors of the gut-brain axis:

• visceral hyperalgesia: hypersensitivity to normal intestinal distension and normal amounts of gas
• altered central sensory processing, emotional arousal and prefrontal cortical abnormalities
• altered intestinal motility: slower colonic transit in constipation, faster transit in diarrhea; in postprandial discomfort an exaggerated gastrocolic reflex
• post-infectious IBS: 6–17% of patients report onset after an episode of acute gastroenteritis
• low-grade mucosal inflammation through immune activation and altered gut microbiota
• poorly absorbed, fermentable carbohydrates (FODMAPs) can increase colonic motility and secretion; fat may increase intestinal permeability and hypersensitivity
• hormonal fluctuations: rectal sensitivity is increased during menses

Psychosocial factors: psychological distress is common, especially in patients seeking medical care; anxiety disorders, depression, somatization disorder and sleep disturbances occur more often.

Clinical features

Symptoms occur in bouts at irregular intervals and rarely wake the patient; they are often triggered by food or stress. Typical features are abdominal pain, often in the lower abdomen, steady or cramping and related to defecation, together with changes in stool frequency and consistency. Patients may also report straining, urgency, a feeling of incomplete evacuation, passage of mucus, and bloating or abdominal distension. Many also have dyspeptic symptoms. Extraintestinal symptoms such as fatigue, fibromyalgia, sleep disturbances and chronic headaches are common.

On examination, patients usually appear healthy; there may be tenderness, particularly in the left lower quadrant, sometimes with a palpable, tender sigmoid colon.

Red flags requiring more intensive evaluation:

• age 50 years or older
• loss of body weight
• rectal bleeding, iron deficiency anemia
• family history of colon cancer, inflammatory bowel disease or celiac disease
• nocturnal diarrhea

New or changed symptoms during the course (e.g. fever, persistent vomiting, steatorrhea, symptoms waking the patient, steady worsening) also suggest an additional disease.

Diagnosis

Rome IV criteria

The Rome IV criteria require recurrent abdominal pain on average at least one day per week in the last three months, with symptom onset more than six months earlier, associated with at least two of the following features:

• pain related to defecation
• change in stool frequency
• change in stool consistency

In the absence of red flags, the diagnosis can be made on the basis of these criteria.

Investigations

• History: pain character, bowel habits, drugs taken, eating habits, family situation, psychological and medical comorbidities, quality of life
• Physical examination including digital rectal examination with a test for occult blood; in women a pelvic examination (ovarian tumors, cysts, endometriosis)
• Laboratory tests: complete blood count and biochemical profile including liver tests
• With diarrhea: celiac serology (tissue transglutaminase IgA with total IgA), fecal calprotectin or lactoferrin and CRP or ESR
• With constipation: TSH and calcium
• Testing for pathogens (e.g. Giardia) only if infection is specifically suspected
• Colonoscopy: The mucosa is normal in IBS; in chronic diarrhea, biopsies to exclude microscopic colitis
• further tests (e.g. for carbohydrate intolerance, bacterial overgrowth, pancreatic elastase) only if there are corresponding clues

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Irritable Bowel Syndrome (IBS)
2. StatPearls: Irritable Bowel Syndrome
3. DGVS/DGNM: Update S3-Leitlinie Reizdarmsyndrom (AWMF 021-016, 2021)

Cross-references