Diarrhea/Malassimilation

(Gastroenterology 1999;116:1461-63 & 1464-84)

DEFINITION:

Stool output more than 200 g/day or increased frequency & decreased consistency of stool (can be altered by diet, so these are imperfect criteria but the best we have)
Note, is the patients complaint really diarrhea? Always ask about fecal incontinence “do you have accidents?”; Many complain of diarrhea due to embarrassment
MOA: incomplete absorption of fluid; Normal stool 25% solid, 75% water; Normal fecal water output 80 ml/day representing 1% of GI fluid load
- Fluid load 9-10 L/day: 2 L food/drink, 1.5 L saliva, 2.5 L gastric juice, 1.5 L bile, 2.5 L pancreatic juice; Jejunum/ileum absorb most
- Colon absorbs more than 90% of fluid reaching it, leaving only 1% of original fluid entering the jejunum to be excreted in stool

Classify and categorize diarrhea via: Acute or Chronic, followed by:

Inflammatory
Watery (Osmotic/Secretory)
Malassimilation (Fatty Diarrhea)
Motility/Functional

INFLAMMATORY (fever, hematochezia, abdominal pain)

Infectious
Radiation enteritis
IBD (Ulcerative colitis, Crohn’s)
Ischemic colitis

Infectious – See also Bowel- Diarrheal Infections (Chapter 2.13) for specifics on each bug

Acute
- Cytotonic/Preformed toxins/Enterotoxin (“food poisoning”; typical onset <24 hrs):
  - S. aureus; C. perfringens; B. cereus
- Viral gastroenteritis often has nausea/vomiting, (no high fever), severe abdominal pain, or bloody diarrhea; Brief/self-limiting
  - Rotovirus; Norwalk; Adenovirus; Astrovirus
- Non-Invasive Bacteria
  
  Cytotonic: toxin activation of intracellular enzymes: watery diarrhea; (No fecal WBC or Blood)
  - Enterotoxigenic E. coli (ETEC); Enteropathogenic E. coli (EPEC); Vibrio cholera
  Cytotoxic: toxins cause structural injury: mucosal inflammation and bleeding; (+ fecal WBC (inflammatory) and blood)
  - Enterohemorrhagic E. coli 0157:H7 (EHEC); C. difficile
- Invasive Bacteria (+ fecal WBC and blood)
  - Campylobacter (most common); Salmonella; Shigella; Enteroinvasive E. coli (EIEC); Vibrio parahemolyticus; Yersinia
- Parasites (erratic shedding, need 3 collections for O&P for best chance of detection)
  - Giardia; Entamoeba histolytica
- Opportunistic:
  - Cryptosporidia, Isospora, Microsporidia, Cyclospora, MAC, CMV
Chronic
- Giardia, E. hystolytica, C. difficile, Opportunistic organisms listed above

WATERY DIARRHEA:

Osmotic: (↓ diarrhea with fasting, osmotic gap >50, normal fecal fat) Ingestion of a poorly absorbed substance

Medications: antacids (containing mag and/or phos), lactulose, sorbitol (i.e. ‘sugar-free’ products or elixir medicines), antibiotics
- Antibiotic associated diarrhea: 1. C. difficile or 2. Osmotic diarrhea secondary to impaired colon fermentation of carbohydrates (CHO):
  
  Normally CHO not absorbed in small bowel, undergo colon fermentation to organic acids, which are absorbed and provide mucosal cell energy to absorb water and ions; Antibiotics reduce colon bacteria = ↓ fermentation of organic acids and mucosal energy = net ↓ water reabsorption; Also unabsorbed CHO can cause osmotic diarrhea
Lactose intolerance: primary and secondary mucosal abnormalities, viral/bacterial enteritis, bowel resection; Clinical: bloating, flatulence, discomfort, diarrhea
- Diagnosis: lactose hydrogen breath test or empiric lactose free diet
- Treatment: lactose-free diet, use of lactaid milk and lactase enzyme tablets

Secretory: (no change in diarrhea with fasting, normal osmotic gap, large volume) Failure to absorb electrolytes or stimulation of electrolyte secretion