02. Diarrhea

Resident Editor: Jessica Valente, M.D.

Faculty Editor: Najwa El-Nachef, M.D.

BOTTOM LINE

✔ Diarrhea = More than 3 loose or watery stools /day. Consider impaction, incontinence and factitious diarrhea.

✔ Triage appropriately (Hospitalization? GI referral?)

✔ Determine whether acute (< 2 wks) or chronic (> 4 wks)

✔ Acute diarrhea most likely toxic/infectious; workup only if red flags

✔ Chronic diarrhea workup is guided by 3 categories: watery (secretory vs osmotic vs functional), fatty (malabsorptive vs maldigestive), inflammatory

✔ Osmotic diarrhea improves with fasting, secretory does not

✔ Stool osmotic gap = stool osmolality - 2x(stool Na + stool K). Gap used to distinguish secretory vs. osmotic

✔ Tx based on underlying etiology, most often supportive care

Background

  • Good working definition is >3 loose or watery stools per day
  • Acute: Less than 2 weeks
  • Chronic: Greater than 4 weeks

Signs and Symptoms: 5 Step Approach

  1. Does the patient really have diarrhea? Consider fecal impaction and incontinence
  2. Medication review: check for temporal relationship between new meds & diarrhea onset
  3. Distinguish acute (< 2 weeks) vs. chronic diarrhea (> 4 weeks);
  • Acute diarrhea is most likely infectious. It is usually self-limited and does not require workup unless: Age > 65y, immunocompromised (including pregnancy), significant volume depletion, blood in stool, fever, severe abdominal pain, recent abx, known or suspected IBD, employment as a food handler, recent travel. 20-40% of acute diarrheal symptoms remain undiagnosed.
  1. To organize workup, categorize the diarrhea as inflammatory, fatty, or watery
  • Inflammatory: frequent small volume stools, blood, tenesmus, fever, severe abdominal pain, + fecal leukocytes (poor specificity) or fecal calprotectin; usually requires colo for dx
  • Fatty: oily stools that float and are hard to flush, wt loss, bulky stools; Ddx: Malabsorption vs Maldigestion. +Qualitative fecal fat stain
  • Watery: secretory vs. osmotic vs. functional: calculate stool osmotic gap. Osmotic diarrhea improves with fasting, secretory does not.  Osmotic is due to poorly absorbed ions or sugars; Secretory is most commonly infectious, but also consider peptide-secreting endocrine tumor; Functional is IBS
  1. Consider factitious diarrhea (up to 15% of chronic diarrhea)
  • Stool osm cannot be less than plasma; values <290 can only be from dilution of stool with water/urine
  • Stool osm >600 can only be from dilution with hypertonic solutions
  • Pseudomelanosis coli on colonoscopy suggests anthraquinone laxative (senna, cascara, rhubarb) and takes ~ 9 months to develop. Not pathognomonic, as inflammatory conditions can also cause pseudomelanosis coli.
  • Elevated stool Mg level ( > 108 mg/dL) would be suspicious for Mg-induced diarrhea.

Differential Diagnosis

  • Acute diarrhea: usually toxic/infectious from fecal-oral route, person-to-person; usually self-limited
  • Chronic: watery, fatty, inflammatory causes
  • Always ask about medications!

Watery: secretory vs osmotic vs functional

Stool osmotic gap = 290 - 2x(stool Na + stool K)

Fatty: malabsoprtive or maldigestive

Inflammatory
  • Secretory (stool osm gap <50):  infections, microscopic colitis, alcoholism, hyperthyroidism, bile salt mal-absorption, peptide secreting endocrine tumors, and medications
  • Osmotic (stool osm gap > 125): lactose intolerance, laxatives, sorbitol (gum), antacids, medications, Celiac disease, small intestinal bacterial overgrowth
  • Functional: irritable bowel syndrome. Screen for celiac (anti-TTG and IgA anti-endomysial antibody) and iron deficiency anemia

 
  • Malabsorptive: Celiac disease, gastric bypass, bacterial overgrowth, medications (orlistat, acarbose), giardia, short-gut syndrome, Whipple disease
  • Maldigestive: bile acid malabsorption, pancreatic insufficiency
  • IBD (Crohn’s disease and ulcerative colitis)
  • Radiation enteritis
  • Ischemic colitis
  • Invasive infections: CMV, TB, Entameoba, C diff, Salmonella, Shigella, Campylobacter, EHEC
  • Neoplasia

 

Evaluation

  • Key pieces of history:

Acute Diarrhea

Chronic Diarrhea
  • Onset 20-30 min after meal, or exposure to improperly cooked or stored food: consider bacteria with preformed toxin (sx develop within 6 hours - S. aureus, B. cereus). Often associated with vomiting.
  • Familial outbreak or close contacts (dorm, cruise, etc): consider viral etiology
  • Daycare or childcare center: viral etiologies (norovirus, rotavirus), giardia, cryptosporidium parvum
  • Recent antibiotics or hospitalization: consider C. difficile
  • Recent camping or exposure to fresh water (lakes): consider Giardia lamblia
  • Recent travel to developing country: consider E. coli (traveler’s diarrhea)
  • Bloody stools: consider Enterohemorrhagic E coli EHEC, Shigella
  • Absence of fecal leukocytes: consider toxigenic bacterial infection, giardiasis, and viral infections
  • New medications (PPIs)
  • MSM: bacterial & parasitic pathogens (giardia), proctitis from STDs
  • HIV/immunocompromised state: viral etiologies, C.diff, cryptosporidium, listeria, cyclospora, entamoeba
  • History of cirrhosis or disorders of iron: yersinia, vibrio
  • Blood or mucous in stool: consider IBD
  • Response to fasting: osmotic diarrhea improves and secretory diarrhea persists
  • Greasy stools, stools that float: consider pancreatic insufficiency
  • Ask about bloating, discomfort, alternation with constipation consistent with IBS; Rome criteria without alarm sx
  • Alarm symptoms: blood in stool, nocturnal diarrhea, progressive abdominal pain, weight loss

 
  • Physical: abdominal exam, rectal exam +/- anoscopy if concern for proctitis, stool guaiac if history of bloody stool, evaluate for volume depletion.

 

  • Labs/tests:

Acute diarrhea

Chronic Diarrhea
  • USUALLY NO WORKUP REQUIRED.
  • Consider CBC, BMP (if signs of dehydration), stool electrolytes (calculate stool osmotic gap), stool culture / O&P / C. difficile if risk factors (see 5 step approach above)
  • Depends on whether it is watery, fatty, or inflammatory
  • O&P (sent on 3 consecutive days)
  • Medication and diet review

 

Watery: secretory vs osmotic vs functional

Stool osmotic gap = 290 - 2x(stool Na + stool K)

Fatty: malabsoprtive or maldigestive

Inflammatory
  • Calculate stool osmotic gap using formula above
  • Secretory (gap<50)
    • stool O+P, stool C+S
    • TSH, ACTH, consider hormone-secreting tumors
    • Refer to GI for colonoscopy
  • Osmotic (gap>125): r/o lactose intolerance (H2 breath test), consider laxative screen
  • Functional (gap 50-125): likely IBS but r/o celiac (IgA anti-TTG, IgA anti-EMA)
  • Fecal fat stain
  • Often trial empiric pancreatic enzymes first
  • Refer to GI for further cost-effective workup (colonoscopy with biopsy, quantitative fat stain, stool elastase or chymotrypsin level)
  • Stool analysis
  • Refer to GI for colonoscopy with biopsy
  • Consider CT if neutropenic, concern for severe complications of diarrhea

 

Treatment

  • Fluid replacement and BRAT diet for all
    • BRAT diet: Bananas, Rice, Apple sauce, Toast (low fiber)
  • Acute diarrhea: empiric antibiotics (cipro 500mg bid x5 days) if: immunosuppressed, severe disease, fevers, valvular/vascular/orthopedic prostheses, congenital hemolytic anemias; consider if very young/very old 
    • Treatment depends on underlying cause
    • Viral – Supportive treatment, rehydration. Can give Lomotil or other antidiarrheal PRN IF no fevers or bloody stool
    • C. difficile–
    • Vancomycin 125mg PO 4x/day for 10 days if first episode
    • Traveler’s diarrhea - ciprofloxacin 500 mg PO BID for 3-5 days, although consider FQ resistance  azithromycin 500mg PO daily for 3 days OR azithromycin 1g once
    • Giardia - Metronidazole 500mg PO BID x 14 days 
  • Lactose or other food intolerances – dietary modifications, lactase supplements or products (Lactaid)
  • Celiac disease – gluten free diet
  • Avoid antidiarrheal agents for C. difficile and other bacterial etiologies to avoid risk of toxic megacolon. Can consider probiotics as alternative.
  • IBS – management includes dietary changes, fermentable oligo-, di-, and monosaccharides and polyols [FODMAPs], probiotics, anxiolytics and other medications, complimentary therapy

When to admit

  • Admit patients to hospital for signs of severe volume depletion or malnutrition, especially in the elderly; acute symptomatic bloody diarrhea with anemia; severe diarrhea with abdominal pain and recent antibiotics or hospitalization (concern for C. diff with fulminant colitis)

When to refer

  • Refer patients to gastroenterology for chronic diarrhea with negative initial w/u who may need colonoscopy, or for red flag symptoms (bloody diarrhea, weight loss, older age).

 

References

Barr W & Smith A. Acute Diarrhea in Adults. Am Fam Phys. 2014; 89(3): 180-189.

Corinaldesi R, Stanghellini V, Barbara G et al. Clinical approach to diarrhea. Intern Emerg Med. 2012;Suppl 3:S255-S262.

Juckett G, Trivedi R. Chronic Diarrhea. Am Fam Phys. 2011;84(10):1119-1126.

Schiller LR, Pardi DS, & Sellin JH. Chronic diarrhea: Diagnosis and management. Clin Gastroenterol Hepatol. 2017; 15(2): 182-193.

Sweetser S. Evaluating the Patient with Diarrhea: A Case-Based Approach. Mayo Clinic Proc. 2012;87(6):596-602.