Diarrhea

Diarrheal diseases are very common and, in most cases, self-limiting. Diarrhea is defined either as the presence of more than three bowel movements per day, water content exceeding 75%, or a stool quantity of at least 200–250 g per day. Acute diarrhea lasts for no longer than 14 days and is typically caused by viral or bacterial infection or food poisoning. Chronic diarrhea is often caused by underlying gastrointestinal or endocrinological conditions, such as inflammatory bowel disease or hyperthyroidism. Further symptoms may include fever, bloody stools, abdominal pain, and nausea and vomiting in cases of gastroenteritis. Diagnostic tests for acute diarrhea are usually unnecessary, but they may include CBC, stool samples, or colonoscopy for severe or chronic cases. Most cases of diarrhea only require symptomatic treatment, such as oral rehydration, while severe cases may necessitate administration of antibiotics and hospitalization for IV fluid replacement.

• Diarrhea is present if one of the following criteria is fulfilled: ^[1][2]
  1. Frequent defecation: ≥ 3 times per day
  2. Altered stool consistency: increased water content
  3. Increase in stool quantity: more than 200–250 g per day
• Acute diarrhea: lasting ≤ 14 days
• Persistent diarrhea: lasting > 14 days
• Chronic diarrhea: lasting > 30 days

Overview of pathogens causing watery and bloody diarrhea

Infectious causes ^[1][3]

Noninfectious ^[5][6][7]

Disease transmission and risk factors ^[1]

• Fecal-oral transmission
  • Ingestion of contaminated food or beverages (see “Traveler's diarrhea”)
  • Direct contact with contaminated surfaces or objects (e.g., touching bathroom surfaces or diapers and then touching mouth, nose, or eyes, or handling food without washing hands)
  • Direct contact with a sick individual (e.g., shaking hands, sharing food)
• Risk factors
  • Daycare attendance, nursing home residency, hospitalization
  • Poor hygiene
  • Animal exposure

The loss of bicarbonate-rich fluid in severe diarrhea may cause nonanion gap metabolic acidosis.

• Acute or chronic diarrhea (see “Definition” above)
• Further possible symptoms ^[9]
  • Fever
  • Abdominal pain and cramping
  • Blood in stool
  • Nausea and vomiting in cases of gastroenteritis
  • Signs of dehydration (e.g., low blood pressure, dry mucous membranes, decreased urine output) in severe cases
  • Chronic cases: malnutrition and, in children, failure to thrive
• Disease courses can range from mild to severe with need of hospitalization.

Traveler's diarrhea ^[10]

• Definition: infections which typically occur in patients with a history of recent travel
• Epidemiology
  • Very common while traveling in Asian (“Delhi belly”), African, and Latin American countries ("Montezuma's Revenge")
  • A major cause of diarrhea among children in developing countries
• Etiology
  • Most commonly caused by enterotoxigenic Escherichia coli (ETEC)
  • Other pathogens: C. jejuni, Shigella spp., Salmonella spp., other E. coli strains (e.g., EAEC), protozoa (e.g., Giardia), viral diarrhea (norovirus, rotavirus, astrovirus)
• Clinical features: exudative-inflammatory diarrhea or secretory diarrhea

Factitious diarrhea

• Definition: self-induced diarrhea, usually by laxative abuse (often occurs in individuals with factitious disorders)
• Epidemiology
  • Most prevalent in women
  • Patients are usually employed in the health field.
  • History of multiple hospital admissions
• Clinical features: chronic watery diarrhea without an identifiable cause
• Diagnostics
  • Laboratory tests: metabolic acidosis , metabolic alkalosis , hypokalemia, hypermagnesemia
  • Colonoscopy: may show melanosis coli in cases of anthraquinone abuse (e.g., senna, aloe vera)
• Treatment
  • Correction of electrolyte disturbances and dehydration
  • Referral to psychotherapy

Laxative abuse

• Substances
  • Bulking agent: flaxseed
  • Osmotic laxatives: lactulose, macrogols (polyethylene glycol), magnesium sulfate, sodium sulfate
  • Diphenolic laxatives: bisacodyl, sodium picosulfate
  • Anthraquinones: senna, aloe vera, rhubarb
• Clinical features
  • Osmotic diarrhea, meteorism
  • Dehydration
  • Hypokalemia
  • Melanosis coli: benign hyperpigmentation of the colonic mucosa caused by anthraquinone abuse
    • Colonoscopy: dark brown pigmentation of the colon, interspersed with pale patches reflecting lymph follicles
    • Biopsy: lipofuscin-laden macrophages on PAS staining

The workup for diarrhea includes a detailed patient history (e.g., recent travel), physical examination, and laboratory tests to assess severe cases.

Laboratory tests

Laboratory tests are usually not required in acute cases and are instead reserved for the diagnosis of severe or chronic disease.

• Indications
  • Diarrhea lasting > 4 days
  • High fever
  • Blood in stools
  • Suspicion of IBD
  • Immunosuppression
• Tests
  • CBC: may show anemia or leukocytosis
  • Stool samples: leukocytes, ova, and/or parasites
  • Stool culture: a test used to identify bacteria, viruses, fungi, or parasites in stool, often in the context of a suspected gastrointestinal infection.
    • Stool cultures are not generally recommended, as the tests are expensive and have low sensitivity.
    • Indications: suspected invasive bacterial enteritis, severe illness, or fever (> 38.5°), required hospitalization, and/or stool tests positive for leukocytes/occult blood/lactoferrin
  • C. difficile toxin assay
  • Stool osmotic gap: an equation used to identify if watery diarrhea has an osmotic or secretory etiology
    • Equation: 290 - [2x (stool sodium + stool potassium)]
    • Interpretation
      • A low stool osmotic gap (< 50 mOsm/Kg) is suggestive of secretory diarrhea
      • A high gap (> 100 mOsm/Kg) is suggestive of osmotic diarrhea

Stool osmotic gap overview

Imaging

• Colonoscopy: in patients with chronic diarrhea without an identifiable cause
• CT: if diverticulitis or IBD is suspected

Because most cases of acute diarrhea are self-limited, symptomatic treatment is most common, focusing on oral rehydration. Therapy rarely involves medication.

• Rehydration (especially important in children)
  • Mild to moderate dehydration: oral rehydration therapy with electrolyte-containing fluids, e.g., apple juice or oral rehydration solution
  • Severe cases: consider hospitalization; hydration with IV 0.9% sodium chloride
• Antidiarrheal agents (e.g., loperamide)
  • Indicated in mild to moderate cases
  • Should be avoided if there is fever or blood in stools (indicative of systemic disease)
  • Loperamide is the best initial treatment for chemotherapy-induced diarrhea.
• Antibiotics: are generally not indicated
• Other: treatment of the underlying condition in the case of chronic diarrhea

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