Approach to diarrhea (chronic): Clinical sciences

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Introduction0:00–0:25

Chronic diarrhea is defined as more than three loose stools per day for at least four weeks. Now, based on the underlying cause, chronic diarrhea can be divided into several types, including steatorrhea, secretory, osmotic, inflammatory, dysmotile, and iatrogenic diarrhea.
Now, if your patient presents with chronic diarrhea, first, obtain a focused history and physical examination. Your patient will typically report having more than 3 loose stools per day, or a significant change in stooling habits for at least 4 weeks.

Focused H&P0:25–0:50

In some cases, your patient might report abdominal pain. Physical examination may reveal abdominal tenderness and hyperactive bowel sounds.
With these findings, you should suspect chronic diarrhea, so your next step is to assess the type of chronic diarrhea. To do so, order labs, which could include CBC with differential, CMP, vitamins including A, D, B12, and K, along with iron and calcium levels.

Assess Type0:50–1:58

You could also order inflammatory markers, such as ESR and CRP, as well as TSH and a tissue transglutaminase IgA test. Lastly, other helpful stool studies include stool electrolytes, fecal fat content, occult blood, and tests for fecal calprotectin or lactoferrin.
Now, here’s a clinical pearl! Keep in mind that the labs you choose to order in a particular situation will depend on the history and physical examination.
For example, if your assessment findings suggest inflammatory diarrhea, you’ll need to order fecal calprotectin or lactoferrin.
These are proteins found in neutrophils, which are released during cell lysis, and their detection in stool samples indicates an inflammatory process in the gastrointestinal tract.
First, let’s focus on individuals with steatorrhea! In this case, your patient will often describe their stool as greasy, foul-smelling, and difficult to flush.

Steatorrhea1:58–2:32

They might also report increased flatus and weight loss. Labs typically reveal low levels of albumin, vitamins A, D, B12, and K, along with low iron and calcium; while the stool studies will show an elevated fecal fat content.
These findings are highly suggestive of steatorrhea, so your next step is to assess the underlying cause! If your patient has a family history of autoimmune disease, and their labs reveal positive tissue transglutaminase IgA antibodies, consider celiac sprue.

Celiac Sprue2:32–3:00

In this case, order an upper gastrointestinal endoscopy with small intestinal biopsies. If the biopsies reveal villous atrophy, crypt hyperplasia and an increased number of intraepithelial lymphocytes, diagnose celiac sprue, otherwise known as celiac disease.

Pancreatic insufficiency3:00–3:55

However, if your patient also has a history of alcohol use disorder, chronic pancreatitis, or other disorders affecting the pancreas like cystic fibrosis, consider pancreatic insufficiency!
In this case, check the patient’s amylase and lipase levels and order a fecal pancreatic elastase-1 test. The fecal pancreatic elastase-1 test measures the levels of a pancreatic enzyme called chymotrypsin-like elastase in the stool.
Because it doesn’t degrade as it makes its way through the intestine, it’s a reliable marker of pancreatic function. Additionally, consider ordering a CT scan of the abdomen.
If the amylase and lipase levels are normal, the fecal pancreatic elastase-1 is 200 micrograms per gram or less, and the CT scan reveals pancreatic calcifications, you can diagnose pancreatic insufficiency as a cause of steatorrhea.

Secretory/Osmotic Diarrhea3:55–4:42

Next, let’s take a look at individuals that are reporting watery stools! In this case, consider secretory or osmotic diarrhea.
Your next step is to calculate the stool osmotic gap. Here’s a clinical pearl to keep in mind!
Stool osmolarity is normally the same as plasma osmolarity, around 290 milliosmoles per kilogram, and is primarily determined by sodium, potassium, and water concentrations in the stool.
To calculate the stool osmotic gap, add the stool sodium level to the stool potassium level, multiply the sum by two, then subtract the product from 290.
A normal stool osmotic gap is usually less than 50 milliosmoles per kilogram. Now, if the stool osmotic gap is less than 50 milliosmoles per kilogram, and your patient reports stool volume that’s greater than 200 milliliters per day that does not change with fasting, diagnose secretory diarrhea.

Secretory Diarrhea4:42–5:18

Secretory diarrhea typically occurs due to either malabsorption or intestinal hypersecretion of ions, such as sodium, potassium, chloride, and bicarbonate.
This causes water to move across the intestinal lining into the lumen, resulting in a normal stool osmolar gap! Next, assess the underlying cause of secretory diarrhea.

Bile Acid Diarrhea5:18–5:53

If your patient has a history of Crohn ileitis or a terminal ileum resection, consider bile acid diarrhea, which results from excessive bile acids in the gastrointestinal lumen.
To confirm the diagnosis, order a fecal bile acid level or start an empiric trial of bile acid sequestrant medication. If the bile acid excretion level is elevated, or there’s improvement in stooling when taking bile acid sequestrants, diagnose bile acid diarrhea.
However, if secretory diarrhea is associated with a report of episodic cutaneous flushing and venous telangiectasias on physical exam, consider carcinoid syndrome, and order a 24-hour urine collection for 5-hydroxyindoleacetic acid, or 5-HIAA, which is the end product of serotonin metabolism.

Carcinoid Syndrome5:53–6:37

High levels of 5-HIAA suggest carcinoid syndrome. In addition to carcinoid syndrome, several other hormone-producing tumors can also cause secretory diarrhea.
These include VIPoma, medullary thyroid cancer, mastocytosis, gastrinoma, and colorectal villous adenoma. Okay, now let’s take a step back and return to the stool osmotic gap.

Osmotic Diarrhea6:37–7:12

If the stool osmotic gap is greater than 75 milliosmoles per kilogram, and your patient has a daily stool volume of less than 200 milliliters that further decreases when fasting, diagnose osmotic diarrhea.
Osmotic diarrhea occurs when non-absorbable solutes in the intestinal lumen cause an osmolarity imbalance, eventually moving water into the lumen to restore balance, resulting in normal stool osmolarity.
Once you diagnose osmotic diarrhea, your next step is to assess the underlying cause. If your patient is taking osmotic laxatives, such as polyethylene glycol or lactulose, then consider diarrhea caused by an osmotic laxative.

Osmotic Laxatives7:12–7:35

In this case, discontinue or decrease the dose of the laxative, and if symptoms improve, diagnose diarrhea caused by an osmotic laxative!
However, if there’s a family history of lactose intolerance or the patient's loose stools are associated with ingesting lactose-containing foods, such as milk and ice cream, consider lactase deficiency.

Lactase Deficiency7:35–7:58

To confirm, instruct your patient to avoid lactose-containing foods, and if the diarrhea improves, diagnose lactase deficiency.
Alright, now let’s switch gears and have a look at inflammatory diarrhea! These patients will typically report frequent, small-volume stools, usually in combination with fever and tenesmus, or the urge to pass stool.

Inflammatory diarrhea7:58–8:45

Labs usually reveal low hemoglobin and elevated inflammatory markers, such as ESR and CRP. Additionally, there might be low levels of vitamins A, D, B12, K, and iron.
Finally, if stool studies reveal elevated fecal calprotectin or lactoferrin, diagnose inflammatory diarrhea. Your next step is to assess the underlying cause, which typically includes conditions like ulcerative colitis, Crohn disease, and eosinophilic gastroenteritis!
First, let’s focus on ulcerative colitis! In this case, history will usually reveal colicky abdominal pain, bloody diarrhea, and sometimes, extraintestinal symptoms, like joint or eye pain.

Ulcerative colitis8:45–9:51

Additionally, the physical exam will typically reveal an abdomen that’s tender to palpation, possibly in combination with bright red blood and discomfort on a digital rectal exam.
Finally, you might notice skin changes, like tender red spots that indicate erythema nodosum. With these findings, you should consider ulcerative colitis, so your next step is to order a gastrointestinal endoscopy with biopsies!
Common endoscopic features of ulcerative colitis include erythema, friability, and ulcerations in a continuous pattern that typically affects the rectum!
In some cases, the inflammation can spread to the ileum, which is called backwash ileitis! Additionally, if histopathology reveals mucosal and submucosal inflammation and crypt abscesses, diagnose ulcerative colitis.
Now, let’s take a look at Crohn disease! In this case, history will typically reveal postprandial abdominal pain, non-bloody diarrhea, possibly in combination with extraintestinal symptoms like joint or eye pain.

Crohn disease9:51–10:54

*** Additionally, the physical exam usually reveals abdominal tenderness and possibly an abdominal mass. In some cases, you might find perianal mass, fistulas, or even fissures, as well as skin changes, such as erythema nodosum.
With these findings, consider Crohn disease and order a gastrointestinal endoscopy with biopsies! Important endoscopic features of Crohn disease include cobblestoning and deep, linear, serpiginous ulcerations, with a discontinuous pattern, or “skip lesions,” where segments of normal bowel are interspersed with large areas of diseased bowel.
Typically, the rectum is spared. Finally, if histopathology reveals transmural chronic inflammation, with or without granulomas, diagnose Crohn disease!

Eosinophilic gastroenteritis10:54–11:20

Next, let’s go over eosinophilic gastroenteritis! If your patient has a history of asthma, eczema, or food sensitivities, and labs show elevated serum eosinophils, consider eosinophilic gastroenteritis.
Order a gastrointestinal endoscopy with biopsies, and if histopathology shows eosinophilic infiltration of the intestinal mucosa, diagnose eosinophilic gastroenteritis.
Alright, now switching gears and moving on to dysmotile diarrhea! In these individuals, labs are normal, there are no tissue transglutaminase IgA antibodies, and the patient’s stool studies reveal no occult blood.

Dysmotile Diarrhea11:20–11:45

Additionally, fecal calprotectin and lactoferrin are both negative. With these findings, diagnose dysmotile diarrhea!

IBS11:45–12:22

Next, assess the underlying cause. First, let’s focus on irritable bowel syndrome!
These individuals typically report bowel habit changes for at least 6 months, which are usually related to diarrhea or constipation, as well as abdominal pain or discomfort that’s relieved with defecation.
In some cases, the patient may report abdominal bloating, or they might have a history of depression, anxiety, fibromyalgia, trauma, or recent infectious gastroenteritis.
If in addition to these findings, the labs reveal a normal TSH, diagnose irritable bowel syndrome! However, if your patient reports palpitations and heat intolerance, and their labs reveal low TSH levels, consider hyperthyroidism.

Hyperthyroidism12:22–12:42

In this case, order serum free T3 and free T4, and if elevated, diagnose hyperthyroidism as the cause of diarrhea. Finally, let’s take a look at chronic diarrhea due to iatrogenic causes!

Chronic diarrhea due to iatrogenic causes12:42–13:13

Patients will typically present with a history of abdominal surgery, such as cholecystectomy, ileal resection, bariatric surgery, or vagotomy with fundoplication.
If the patient’s labs are normal and stool studies reveal no occult fecal blood and negative fecal calprotectin or lactoferrin levels, diagnose chronic diarrhea due to iatrogenic causes, such as abdominal surgical procedures.
Alright, as a quick recap… Chronic diarrhea is defined as more than three loose stools per day for at least 4 weeks. Based on the underlying cause, chronic diarrhea can be divided into several types, including steatorrhea, secretory, osmotic, inflammatory, dysmotile,

Review13:13–13:32

Approach to diarrhea (chronic): Video, Steps, Uses | Osmosis