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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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