Priority Topic: Diarrhea

Key Feature 6: In a young person with chronic or recurrent diarrhea, with no red flag symptoms or signs, use established clinical criteria to make a positive diagnosis of irritable bowel syndrome (do not overinvestigate). 
Skill: Clinical Reasoning, Selectivity
Phase: Diagnosis

Key Feature 7: In patients with chronic or recurrent diarrhea, look for both gastro-intestinal and non-gastro-intestinal symptoms and signs suggestive of specific diseases (ex: inflammatory bowel disease, malabsorption syndromes, and compromised immune system). 
Skill: Clinical Reasoning
Phase: History, Physical

According to the UpToDate article, "Clinical manifestations and diagnosis of irritable bowel syndrome in adults" (2018), "Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract characterized by chronic abdominal pain and altered bowel habits." The standard diagnostic criteria for irritable bowel syndrome (IBS) are the Rome IV criteria. A symptom cluster qualifies for a diagnosis of IBS according to these criteria when there is recurrent abdominal pain, on average, at least one day per week in the last three months, associated with two or more of the following criteria:

1. Related to defecation
2. Associated with a change in stool frequency
3. Associated with a change in stool form (appearance)

Note that for a diagnosis of IBS, abdominal pain must be part of the symptom cluster. Abdominal pain, pain with defecation, and constipation and/or diarrhea - all symptoms associated with IBS - by themselves have their own differential diagnosis, and when a clinician is first assessing a patient with such symptoms, they must consider the full diagnostic differential so as not to miss a more ominous disease process. In a patient with suspected IBS based on history and fulfilment of the Rome IV IBS criteria, what are the red flags to look for to decide whether further investigations are warranted before confidently ascribing symptoms to IBS alone?

The UpToDate article cited above provides an approach to the initial evaluation of a patient with a suspected diagnosis of IBS. It includes the following considerations:

• Initial evaluation in all patients with suspected IBS includes a history and physical examination*, and limited testing to evaluate for the presence of alarm features concerning for organic disease.
• In all patients with suspected IBS, we perform a complete blood count and age appropriate colorectal cancer screening.
• In patients with diarrhea, we perform the following:
  • C-reactive protein or fecal calprotectin 
  • Serologic testing for celiac disease
• Alarm features concerning for underling organic disease include:
  • Age of onset after age 50 years
  • Rectal bleeding (more than minimal) or melena
  • Nocturnal diarrhea
  • Progressive abdominal pain
  • Unexplained weight loss
  • Laboratory abnormalities (explained iron deficiency anemia, elevated C-reactive protein or fecal calprotectin)
  • Family history of inflammatory bowel disease, celiac sprue, or colorectal cancer
• In patients who meet diagnostic criteria for IBS and have no alarm features, we do not routinely perform any additional testing beyond the initial evaluation.
• In patients with alarm features, we perform additional evaluation to exclude other causes of similar symptoms. The diagnostic evaluation is based on the clinical presentation and usually includes endoscopic evaluation in all patients and imaging in selected cases.

So in conclusion, if a patient has suspected IBS based on meeting the Rome IV criteria, and if they do not have any red flag features as listed above, then they warrant investigation with a CBC only. If they also have diarrhea (note that a subset of patients with IBS only have constipation without diarrhea), then they also deserve a CRP (or fecal calprotectin) to rule out an inflammatory process, as well as serologic testing for celiac disease. In keeping with general population guidelines, their screening for colorectal cancer should also be UpToDate. If all of the applicable testing is unremarkable, then one can feel fairly confident that the patient truly has a diagnosis of IBS without resorting to exhaustive testing to rule out a multiplicity of possible but improbable differential diagnoses. In my experience, it tends to be patients who request more testing because they are worried there is more worrisome disease going on in their body (which is not surprising since their symptoms can feel very strong and alarming). But further testing just for patient reassurance is not only unnecessary, it can actually do harm. Some of the ways this may manifest is by leading to false positives (positive test results suggestive of disease when disease is not actually present), or by causing more indirect harm by reinforcing the idea that further testing is required in order to be reassured, which perpetuates a cycle of wanting more and more testing for reassurance, and promotes more anxiety and distress. On a population scale, this also leads to significantly increased health care costs without benefit in patient health or quality of life. One of the benefits of medicine today is that we are constantly refining our understanding of when tests are and are not indicated based on studies looking at the outcomes of investigations that are done - one of the reasons that screening guideline recommendations are always changing. More testing is not always a good thing.

*The physical examination of a patient with chronic or recurrent diarrhea is important as there are clues to look for that can help increase or decrease the likelihood of various diseases. It is also useful in classifying the severity of the diarrhea by looking for signs of dehydration. According to the UpToDate article, "Approach to the adult with chronic diarrhea in resource-rich settings" (2018), the physical examination of a patient with chronic diarrhea should include assessment for:

• Findings suggestive of IBD (episcleritis, mouth ulcers, abdominal pain or masses, an anal fissure or fistula, the presence of visible or occult blood on digital examination, a skin rash)
  
• Evidence of malabsorption (physical signs of anemia, scars indicating prior abdominal surgery, wasting)
  
• Lymphadenopathy (possibly suggesting HIV infection)
  
• Abnormal anal sphincter pressure or reflexes (possibly suggesting fecal incontinence)
  
• Examination for exophthalmos and lid retraction, and palpation of the thyroid may provide support for a diagnosis of hyperthyroidism