Home Medicine PA Boards 90: Irritable Bowel Syndrome

PA Boards 90: Irritable Bowel Syndrome


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Irritable bowel syndrome is characterized by abdominal pain without an identifiable cause. This is a pain syndrome that is also accompanied by altered bowel habits. This is the most commonly diagnosed GI disorder and is responsible for up to 30% of the referrals to gastroenterology.

Women are more likely to develop IBS at a rate of 2:1. Average age isn’t defined – because many patients will report having symptoms for many years before finally seeking treatment.

It’s important you communicate to your patients that this is a chronic disease and there isn’t an increased risk of cancer or irritable bowel disease.

The pathophysiology is considered to be multifactorial and isn’t quite understood.

GI motility has been noted to be abnormal in some patients with IBS, but no specific pattern has been identified. The clinical relevance of these abnormalities isn’t certain, but certain medications for IBS focus on stimulating motility and have improved patient outcomes.

Visceral hypersensitivity is also thought to play a role – especially when it comes to bloating and distention. Patients have been noted to have increased pain more notably when distention occurs rapidly. When this happens, it’s thought that receptors are stimulated, and pain signals are sent to the brain.

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Some patients have also been noted to develop IBS after suffering GI infection (post infectious IBS).

Other factors might include genetics, alteration in fecal flora, overgrowth of small intestinal bacteria, food sensitivity (specifically carbohydrate malabsorption and gluten sensitivity), and mood disorders.

The main symptoms is pain – typically felt as a cramping sensation that comes in episodes. The location, severity, and character of the pain are variable – but many have described it to be felt in the LLQ. Having a bowel movement often improves the pain – but doesn’t necessarily rid the pain completely. Pain often times comes following a meal. 

The pain is not associated with weight loss, anorexia, or malnutrition and the pain should not be progressive or awaken the patient at night.

Patients typically have constipation, diarrhea, or a combination of both at some point in the disease.

The diarrhea is not profuse and preceded by cramping and/or urgency. Half the patients will also complain of a mucus discharge.

Large amounts of diarrhea, bloody stools, nocturnal diarrhea, and/or greasy stools are indications of an alternate diagnosis.

The constipation can lasts days to months and patients often report the feeling of incomplete evacuation.

Patients may also experience impaired sexual function, dysmenorrhea, dyspareunia, increased urinary frequency and urgency.

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Rome criteria (mainly used for clinical trials – group similar type patients):Recurrent abdominal pain/discomfort at least three days per month for the last three months and at least two of the following:

1. Improvement with defecation
2. Onset associated with a change in frequency of stool
3. Onset associated with a change in form/appearance of stool

Symptoms that support IBS include:
1. Abnormal stool frequency (≤3 bowel movements per week or >3 bowel movements per day)
2. Abnormal stool form (lumpy/hard or loose/watery)
3. Defecation straining, urgency, or a feeling of incomplete bowel movement
4. Passing mucus and bloating

The Rome criteria is not perfect and definitely has its flaws. But, the American Gastroenterological Association recommends that the diagnosis of IBS should be based upon the identification of positive symptoms consistent with the condition as summarized by the Rome criteria and excluding in a cost-effective manner other conditions with similar clinical presentations.

So, patients who have symptoms suggestive of IBS, without alarm symptoms (rectal bleeding, nocturnal/progressive abdominal pain, weight loss, fever, anorexia, fever, and/or lab abnormalities), and without a family history of colorectal cancer and/or IBD are likely to be diagnosed with this disease.

After one year 75% of patients subtypes (diarrhea, constipation, mixed, or alternating type).

Further workup depends if the patient is presenting with constipation or diarrhea predominant symptoms. Routine imaging and lab testing is not recommended in the young patient with typical IBS symptoms.

Patients with diarrhea should have stool cultures (giardia), celiac disease screening (serum IgA antibody to tissue transglutaminase), twenty four hour stool collection (malabsorption), and/or colonoscopy considered. Patients with constipation should have an abdominal xray (retained stool) and/or colonoscopy considered.

Patients with constipation should have an abdominal xray (retained stool) and/or colonoscopy considered.

Patients who have mild disease which does not impair quality of life should have diet modification and lifestyle changes.

Questioning the patient to find patterns of foods that make symptoms worse will be necessary. Excluding these foods, gas producing foods (beans, onions, celery, carrots, raisins, bananas, apricots, prunes, brussels sprouts, wheat germ, pretzels, and bagels), alcohol, and caffeine has been shown to reduce IBS symptoms.

A low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet is also beneficial in reducing symptoms. Low FODMAP education consists of initially eliminating FODMAPs from the diet for six to eight weeks and then, following symptom resolution, gradual reintroduction of foods high in fermentable carbohydrates to determine individual tolerance to specific fermentable carbohydrates.

A trained dietitian should be helping the patient with this process.

Gluten and lactose may be eliminated from the diet empirically for a couple weeks for patients who are not improving (especially for the diarrhea predominant patient).

Psyllium (fiber) can be offered to constipation predominant type patients. Its efficacy is controversial, but there’s little downside in trying – be aware if may cause bloating and gas, so a low dose should be given.

Medicationwill be given for both flares and to prevent abdominal pain/bloating. First line medication for constipation predominant is going to be with polyethylene glycol. If symptoms persists, consider adding lubiprostone.

PEG is an osmotic laxative. Osmotic laxatives draw water into the bowel because they are hypertonic. You can start at a dose of 17 grams and titrate up to 34 grams daily.

First line for diarrhea predominant symptoms is going to be loperamide 2mg 45 minutes before meals. Loperamide inhibits peristalsis, prolong transit time, and reduce fecal volume. Second line treatment can be with a bile acid sequestrant (cholestyramine). Up to half of patients have bile acid malabsorption – the bile acid stimulates colonic secretion and motility leading to diarrhea.

Lastly, rifaximin is an antibiotic approved for diarrhea predominant as it prevents overgrowth of intestinal bacteria.

Alosetron, a 5-hydroxytryptamine-3 receptor (5HT-3) antagonist, is approved for the treatment of severe diarrhea-predominant IBS in female patients whose symptoms have lasted for six months and who have failed to respond to all other conventional treatment.

Abdominal pain/bloating are treated with antispasmodics. Second line treatment will be with antidepressants.

Antispasmodics include dicyclomine and hyoscyamine and are given on an as needed basis every 4 hours. They both have anticholinergic or antimuscarinic properties.

When these fail, tricyclic antidepressants (amitriptyline) may be given. A side effect with this class is constipation – this might be beneficial in diarrhea predominant type but may cause problems with constipation predominant type patients.

Amitriptyline can be started at 25mg every night. Give the medication for 3-4 weeks before adjusting the dose. If one tricyclic doesn’t work – then another may be tried.

Those with refractory symptoms should be re evaluated to ensure the correct diagnosis was reached.

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