Chronic Diarrhea — Full Text

Chronic diarrhea is defined as either lasting longer than 1 month, or recurrent episodes.  Acute diarrhea can tail-away into low-grade chronic symptoms for 1-2 months, sometimes due to temporary lactose intolerance.  So if a patient has acute diarrhea that eases up a lot but still persists (stools aren’t normal yet), we don’t call it “chronic diarrhea” until 2 months have gone by.   Avoiding dairy products might help.

The possible causes of Chronic Diarrhea are much broader than for Acute Diarrhea; the following list is abbreviated:

Causes of Chronic Diarrhea

xxSuspect / Diagnose by General Clinician
โ€ข Irritable Bowel Syndrome (IBS)
โ€ข Inflammatory Bowel Disease (IBD)
โ€ข Celiac Disease
โ€ข Bacteria / Parasites
โ€ข Malabsorption Syndromes
โ€ข Post-Cholecystectomy Surgery (gallbladder)
Lactose Intolerance
โ€ข Colon Cancer
โ€ข Medications, Laxative Abuse
โ€ข HIV
โ€ข Hyperthyroidism
xxxxLet Gastroenterologist Consider It

โ€ข Chronic Pancreatitis
โ€ข Chronic Diverticulitis
โ€ข Diabetic Autonomic Neuropathy
โ€ข Adrenal Insufficiency (Addisonโ€™s Disease)
โ€ข Carcinoid tumors, Mastocytosis, & other xx xxxxVery Rare Diseases and Infections


Since many or even most patients with chronic diarrhea have the simple, not dangerous (though clearly annoying) Irritable Bowel Syndrome (IBS), or Lactose Intolerance, we don’t want to do extensive work-ups routinely.ย  But Inflammatory Bowel Diseases (IBD)ย  —ย  Crohnโ€™s Disease, Ulcerative Colitis, and the newly identified Microscopic Colitis — cause serious complications and therefore require timely diagnosis, as do other entities in the table.ย  Note the enormous difference in degree of danger between “Inflammatory” vs. โ€œIrritableโ€, and between “Disease” vs. โ€œSyndrome.โ€

On our first visit with the patient, we’ll take a history and perform physical exam, looking for clues to the conditions in the Table. Maybe we’ll find something obvious, like the diarrhea began after starting a new medication, or soon after gallbladder removal. Maybe we note a rapid heart rate, making us think of Hyperthyroidism. But if nothing stands out, we’ll order some laboratory tests (discussed below).

One question for us is whether to refer the patient to a Gastroenterologist, including for a colonoscopy?ย  We decide in part by seeking Red Flags / Key Clues.ย  Diseases below in bold require gastroenterology referral for diagnosis or confirmation, any clinician can diagnose the others.

  • Weight Lossโ€ฆโ€ฆโ€ฆโ€ฆโ€ฆ..โ€ฆ…………………….โ€ฆ…could be Colon Cancer / other serious illnesses
  • Bloody Diarrheaโ€ฆโ€ฆโ€ฆโ€ฆ..โ€ฆ……………………โ€ฆ.maybe IBD, Colon Cancer, Amebic dysentery
  • Severe Diarrhea, esp. if also at nightโ€ฆ………….needs colonoscopy,
  • Significant abdominal pain alsoโ€ฆ……….โ€ฆโ€ฆ…We order CT Scan for Tumors outside the Lumen
  • Age >50 (at onset)โ€ฆโ€ฆ..โ€ฆโ€ฆโ€ฆ…………………….age for Colon Cancer
  • Greasy, Malodorous Stoolsโ€ฆโ€ฆ…………………….Malabsorption
  • Lived / Traveled in poor countriesโ€ฆ……………..Parasites
  • Men having Sex w/ Menโ€ฆโ€ฆโ€ฆโ€ฆโ€ฆ……………….Parasites; HIV; AIDS Infections
  • Family History (IBD, Colon Cancer)……………….IBD, Cancer (rule out by colonoscopy)
  • Immunocompromisedโ€ฆโ€ฆโ€ฆโ€ฆ…………………….Needs extensive work-up

Some Comments on the above:

Weight loss is hard to evaluate without a previous exact weight.  People often have mistaken ideas about their own weight trends, in both directions.  I’ve had patients swear how much they were gaining or losing, but when I check prior weights that were documented in the chart, it’s sometimes the exact opposite!

If we don’t have any definite past weights on our clinic scale, I look at their belt โ€” are tighter notches being used; do looser ones look worn?  Are their pants looser?  [though Iโ€™ve had occasional patients explain how they had to get other clothes due to the weight loss, which is convincing].

Unusual Non-Intestinal Symptoms may sometimes occur in Inflammatory Bowel Disease.   If these are present in a patient with Chronic Diarrhea, we should refer to a Gastroenterologist for colonoscopy.  They include:

  • Inflammatory arthritis (usually hips, knees, spine)
  • Eye Pain (iritis, episcleritis, scleritis)
  • Painful red lumps on shins (Erythema nodosum)
  • Elevated Alkaline Phosphatase in blood test
  • Frequent canker sores in mouth (Aphthous ulcers)

Digression โ€” In 1995, a 33-year-old woman, typical immigrant from rural Mexico with husband & baby, sought care in a famous San Francisco hospital for chronic diarrhea.  She got worked-up for every possible bowel disease, parasites & otherwise, to no avail.  Frustrated, she returned to Mexico โ€” doctors there heard, โ€œLady from San Francisco, chronic diarrhea!โ€ & they nailed the HIV diagnosis without further thought.  We do have our biases & preconceptions!

HIV isnโ€™t a common cause of chronic diarrhea, but everyone should get tested.

If the diarrhea began right after starting a New Medication, we look up its side effects.  If diarrhea is listed (it almost always is, along with nausea, headache, etc. etc.), we might consider a substitution, or try stopping the drug if it isn’t essential.  Read the link as to why we need to exercise Caution when reading Lists of Side Effects.

If chronic diarrhea began soon after gallbladder surgery, we’d suspect Post-Cholecystectomy Syndrome due to bile being dumped directly into the small intestine (it’s normally stored in the gallbladder).  This may occur after 10% of operations.  The medicine cholestyramine may help, but causes all sorts of mild but unpleasant effects.  We could gradually build up to the highest dose tolerated; but since the syndrome may eventually go away on its own, we might have to stop & start a few times to figure it out.

Laboratory Tests

Since Chronic Diarrhea by definition has been bothersome for quite a while, we’d likely order a few basic tests at the first visit.  I start with:

Other tests to consider (see Acute Gastroenteritis for descriptions of the germs):

  • Stool for Ova & Parasitesย  —ย  Especially for Men-having-Sex-with-Men, or people who’ve traveled to / lived in underdeveloped countries.ย  We need to order at least 3 separate specimens
  • Stool for C. difficile —ย  If the patient took antibiotics for something else before the diarrhea began, or was recently hospitalized; also for in immunocompromised patients
  • Stool Culture for Bacteriaย  —ย  Especially for immunocompromised persons
  • Fecal Fatย  —ย  Tests for Malabsorption Syndromes, especially likely if there are frequent greasy, foul-smelling stools.ย  Normally patients have to collect stool for 72 hours, but some labs may be able to test on a single-stool specimen.ย  We might let a Gastroenterologist deal with this, since theyโ€™d be the ones to work-up positive results anyway.

Clinicians should NEVER perform or order a test for “Occult Blood” as work-up for diarrhea.  It should only be used for colon cancer screening on asymptomatic people  over 50.  On a person with diarrhea, a positive is likely to be false-positive for significant disease, & a negative test wouldn’t prove anything diagnostically.

Parasitesย  โ€“ย  Tests for parasites and their eggs (“Ova & Parasites,” abbreviated “O&P”) are rarely positive, even if we obtain 3 separate specimens as recommended.ย  Still, as opposed to Acute Diarrhea, we’re obliged to order them for patients with Chronic Diarrhea.ย  AIDS-related parasites need separate tests, not the standard preserved O&P’s.

For Giardia specifically (the most common parasite), a stool test for “Giardia Antigen” gives better results than the O&P’s.ย  Some test kits can find Cryptosporidium antigen as well.ย  Other possible parasites are Ameba and Trichuris, not usually found in the U.S.ย  Strongyloides can persist for decades, so it’s worth seeking if there’d ever been any travel in underdeveloped countreis.ย  But O&Pโ€™s are notoriously poor for it; we can order a blood antibody test for persons with normal immune systems.

Entamoeba histolytica, the parasite that causes Amebic Dysentery,ย  can cause serious illness years down the line from initial infection.ย  However, looking under the microscope at a standard O&P canโ€™t distinguish it from its harmless relatives Entamoeba dispar or moshkovskii.ย  Lots of gay men in the U.S. are colonized with E. dispar.ย  So if we find โ€œAmeba,โ€ we then send a fresh stool for Antigen Detection to distinguish.ย  We can also order blood antibodies against E. histolytica; that’s most useful if it’s negative, to rule it out (a positive test remains so for life, so could simply mean previous infection).

Then there’s the parasite Blastocystis hominis (now called โ€œBlastocystis sppโ€ since there are many species), which is often identified on an O&P.  Thereโ€™s no good evidence at all that it can cause illness; it’s simply a harmless parasite that labs can find in stool.  Therefore, there’s no evidence about what medicine would work.  Some clinicians like to treat, because thatโ€™s all they found, & donโ€™t know what else to do for the patient.  Iโ€™m skeptical.

One suggested drug regimen I saw, Metronidazole 750 mg, 3 times a day for 10 days, is not easy to tolerate.  One study found some clinical success with 500 mg.  I might be inclined to offer 250 mg for 5 days, which cures any Giardia that might not have been found.  Tinidazole 2 gm daily (50 mg/kg) for 3 days is better tolerated & cures lots of organisms (but may be expensive).

Follow-Up  in 2-3 Weeks

After ordering initial tests, we have patients return for results.ย  More importantly, we weigh them on our same office scale.ย  Weight loss from chronic diarrhea is the main reason to embark on an extensive work-up, including Gastroenterology referral.

If there are no Red Flags or Key Clues noted at our first visit for Chronic Diarrhea, no weight loss on follow-up, and normal lab studies, we make a tentative diagnosis of either Lactose Intolerance and/or, Irritable Bowel Syndrome (IBS), the latter if thereโ€™s also any abdominal pain/discomfort.ย  We treat with dietary changes (avoid dairy products; more fiber), psyllium (Metamucilยฎ), and/or drugs like Loperamide (Imodiumยฎ).

That was quick!?!?  Well, we didnโ€™t find anything, & the above 2 conditions are awfully common.  Lactose Intolerance has no good simple test to document it, & is best addressed by a trial period of avoiding dairy foods or adding commercial โ€œlactaseโ€ products.

We diagnose IBS with Diarrhea (aka IBS-D) by the Manning Criteria โ€” 2 or more of the following 6:

  • Pain relieved with defecation
  • Increased stool frequency at time of pain
  • Diarrheal stools at time of pain
  • Mucus in stool
  • Sensation of incomplete defecation
  • Abdominal bloating on physical exam

Accuracy for IBS depends on sex, age, & number of criteria.  For example:

  • 20 y.o. women: 2 of the 6 criteria (50% accuracy) to 6 of 6 (>90%)
  • 60 y.o. man:  2 of the 6 (25%) to 6 of 6 (70%)

Accuracy for men is always less than for women, and accuracy for everyone decreases after 40 y.o.  IBS is a condition of younger people; personally, Iโ€™d never diagnose it if it first began over 50 without a decent work-up (including colonoscopy).

We treat IBS if we suspect it, only doing work-ups for patients who don’t improve.

Gastroenterologist Referral  โ€“  Any patient with findings suggestive of:

  • Tests suggesting for Inflammatory Bowel Diseaseย  ย โ†’ patient needs a colonoscopy, with biopsies
  • Iron Deficiency with or Without Anemiaย  —ย  We also refer after proving that Anemia is due to low iron, meaning blood loss, which could be from Colon Cancer.ย 
    • First, we’d rule out Celiac Disease (negative blood test for tTP-IgA antibody).ย 
    • We probably wouldn’t refer young women with very heavy menstruation (low likelihood of serious bowel disease by age, more probably IBS, with the anemia due to their periods).
    • Anyone over 40-45 would need a colonoscopy to rule out Colon Cancer.
  • Age over 50ย  —ย  We certainly refer these persons based on age alone, when Colon Cancer is more likely; people over 50 would benefit from colonoscopy anyway (colon cancer screening).
  • Malabsorptionย  —ย  We likely let a Gastroenterologist order the fecal fat test. Even if we’d obtained it & it was negative, we’d still refer if stools are really greasy & malodorous.
  • Weight Lossย  โ€“ย  We refer for sure, for colonoscopy and maybe additional work-up
  • Severe diarrhea (especially if it awakens the patient at night), or significant abdominal pain along with the diarrhea.ย  These patients are more likely to have serious illness.ย  In terms of the abdominal pain, weโ€™d order an abdominal CT Scan to seek tumors outside the lumen.

Whatโ€™s the difference between colonoscopy & flexible sigmoidoscopy?  The latter is certainly cheaper, but doesnโ€™t reach the cecum (where Crohnโ€™s Disease often lurks).  Some studies show the 2 tests are comparable for chronic diarrhea.  The sigmoidoscopy is said to be safer, but the rare dangers of colonoscopy tend to occur over 75 y.o., when chronic diarrhea would need one anyway.

If we refer to a Gastroenterologist, theyโ€™ll assume responsibility for the work-up and address the obscure etiologies in our Table, like rare infections (e.g. intestinal TB) or carcinoid, as indicated.  If we have our own access to directly ordering a colonoscopy, and order the test for a red flag, even if it’s negative, we’d refer to Gastroenterology.  And as for every condition we address in primary care, if we can’t make a diagnosis, & nothing improves, we send to a specialist.

See Chronic Diarrhea for for the clinicianโ€™s condensed thought-process when face-to-face with a patient.

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