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Irritable bowel syndrome

Last updated on September 23, 2021

Irritable bowel syndromeDescription of Medical Condition

Altered bowel habits, abdominal pain, gaseousness, in the absence of organic pathology (divided into four types):

  • Alternating diarrhea with constipation
  • Diarrhea predominant
  • Constipation predominant
  • Upper abdominal bloating and discomfort

System(s) affected: Gastrointestinal

Genetics: Unknown, but more common in families of patients

Incidence/Prevalence in USA:

  • Unknown, but 50% of gastrointestinal visits, and second to upper respiratory infection as cause for lost workdays
  • At least 15% of population (uncommon in children and early teens)

Predominant age:

  • Late 20′s, rarely in late teens
  • If overage 40, other disease more likely

Predominant sex:

  • Female > Male (2:1) in the US
  • In other parts of the world — Male > Female

Medical Symptoms and Signs of Disease

  • All present in most patients but not with every episode
  • Abdominal pain, usually lower quadrant, relieved by defecation
  • Mucus in stools
  • Constipation
  • Diarrhea
  • Distention
  • Upper abdominal discomfort after eating
  • Straining for normal consistency stools
  • Urgency of defecation
  • Feelings of incomplete evacuation
  • Scybalous stools
  • Nausea, vomiting (rarely)
  • Rome II criteria: 12 weeks or more in past 12 months of abdominal bowel pain or discomfort that has 2 out of 3:

– Relieved by defecation

– Onset associated with change in frequency of stool

– Onset associated with change in form of stool

What Causes Disease?

Unknown but patients show some gut motility abnormalities with increased response to stress and stimulants, and increase in the 3 cycles/ minute smooth muscle contractions. Up to 1/3 of patients develop IBS after an episode of gastroenteritis.

Risk Factors

  • Other members of the family with the same or similar gastrointestinal disorder
  • History of childhood sexual abuse
  • Sexual or domestic abuse in women

Diagnosis of Disease

Differential Diagnosis

  • Inflammatory bowel syndromes
  • Lactose intolerance
  • Infections (Giardia lamblia, Entamoeba histo-lytica, Salmonella, Campylobacter, Yersinia. Clostridium difficile)
  • Diverticula
  • Cathartic use
  • Magnesium containing antacids
  • Celiac sprue
  • Pancreatic insufficiency
  • Depression
  • Somatization
  • Adenocarcinoma of the colon
  • Villous adenoma
  • Endocrine tumors
  • Hypo/hyperthyroidism
  • Diabetes mellitus
  • Radiation damage to colon or small bowel


  • As needed to rule out other pathology OESR


– Stool for ova, parasites and culture

Drugs that may alter lab results: N/A

Disorders that may alter lab results: N/A

Pathological Findings

All labs normal except for sigmoidoscopy

Special Tests

Not needed for diagnosis


  • Barium enema, if indicated is usually normal
  • Small bowel series

Diagnostic Procedures

Sigmoidos copy (often normal), can show spasm that reproduces pain and increase mucosal folds

Treatment (Medical Therapy)

Appropriate Health Care


General Measures

  • Heat to abdomen can help
  • Biofeedback may help
  • Reduce stress


As normal


  • Increase fiber — may make some patients worse
  • Avoid — large meals; spicy, fried, fatty foods; milk products, carbohydrates

Patient Education

  • Many materials available nationally and locally
  • Stress the organicity of the disease versus any psycho-social interpretation
  • Teach patient to avoid problem stimulants

Medications (Drugs, Medicines)

Irritable bowel syndromeDrug(s) of Choice

  1. Use from among this list according to need or response
  • Bulk producing agents — psyllium (Metamucil) products 1 tbsp bid or tid
  • Constipating agents (if diarrhea is significant) — loperamide (Imodium) 4 mg initial dose, then 2 mg after each unformed stool or diphenoxylateatropine (Lomotil) 2.5-5.0 mg (1-2 tablets) after each unformed stool
  • Antispasmodics/anticholinergics/sedatives
  • dicyclomine (Bentyl) 10-20 mg bid to qid
  • chlordiazepoxide-clidinium (Librax) 1 or 2 ac and qhs
  • hyoscyamine (Levbid) 0.375 mg bid
  • phenobarbital-scopolamine-hyoscyamine-atropine (Donnatal) 1 or 2 tablets ac and hs
  • amitriptyline (Elavil) 25-50 mg qhs
  • 5-HT4 receptor agonist — tegaserod (Zelnorm) 6 mg bid for 4-6 weeks in patients with prominent constipation, may repeat course once (for women only)
  • Antiflatulents — simethicone (Mylicon) 2 or 4 tablets pc and hs
  • Lactose intolerance — lactase (Lactaid) capsules or tablets; 1-2 tablets prior to ingesting milk products

Contraindications: Refer to manufacturer’s profile of each drug

Precautions: Refer to manufacturer’s profile of each drug

Significant possible interactions: Refer to manufacturer’s profile of each drug

Alternative Drugs


Patient Monitoring

As needed for symptoms

Prevention / Avoidance

See Diet

Possible Complications


Expected Course / Prognosis

• No progression to cancer or inflammatory disease

• Expect recurrences, when under stress, throughout life. Frequency lessens as age increases.


Associated Conditions

  • Migraine
  • Bladder frequency
  • Nocturia
  • Urgency
  • Fecal incontinence
  • Fibromyalgia
  • Dyspareunia
  • Depression
  • Stress incontinence

Age-Related Factors


Pediatric: N/A

Geriatric: N/A


Anecdotal information implies that irritable bowel syndrome gets worse in pregnancy. But there are no increased risks to fetus or mother.


  • Mucous colitis
  • Spastic colon
  • Irritable colon

International Classification of Diseases

564.1 Irritable bowel syndrome

See Also

Other Notes

Must not give patients the impression that this is a psychiatric illness


IBS = irritable bowel syndrome

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