What is diarrhea?

What is Diarrhea?

Diarrhea is a disorder characterized by frequent and watery bowel movements, typically defined as the passage of loose or liquid stools with increased frequency (more than 3 stools per day). 1

Clinical Definition and Classification

Diarrhea can be classified based on several parameters:

Duration-based classification:

• Acute diarrhea: Episode lasting less than 14 days 1
• Persistent diarrhea: Diarrhea lasting 14-29 days 1
• Chronic diarrhea: Diarrhea lasting 30 days or longer 1

Functional impact classification:

• Mild diarrhea: Tolerable, not distressing, does not interfere with planned activities 1
• Moderate diarrhea: Distressing or interferes with planned activities 1
• Severe diarrhea: Incapacitating or completely prevents planned activities; all dysentery (passage of grossly bloody stools) is considered severe 1

Stool frequency classification:

• Traditional classification: 1-2 stools (mild), 3-5 stools (moderate), 6-9 stools (severe) per day 1

Pathophysiology and Types

Diarrhea occurs when the intestine fails to complete absorption of electrolytes and water from luminal contents. The main types include:

• Osmotic diarrhea: Caused by nonabsorbable, osmotically active substances in the intestine 2
• Secretory diarrhea: Results from impaired electrolyte absorption due to various causes including bacterial toxins, reduced absorptive surface area, luminal secretagogues, or circulating secretagogues 2
• Inflammatory diarrhea: Associated with intestinal inflammation, often presenting with blood or mucus in stool 1

Clinical Assessment Tools

Several tools help clinicians assess diarrhea:

• Bristol Stool Form Scale: Helps distinguish stool form and identify loose stools 3
• NCI-CTCAE grading system: Provides standardized grading for diarrhea severity 1
  • Grade 1: Increase of <4 stools per day over baseline
  • Grade 2: Increase of 4-6 stools per day over baseline
  • Grade 3: Increase of ≥7 stools per day over baseline; hospitalization indicated
  • Grade 4: Life-threatening consequences
  • Grade 5: Death

Epidemiology and Impact

Diarrheal diseases represent a significant global health burden:

• Second leading cause of morbidity and mortality worldwide 1
• In the United States alone, diarrheal illness accounts for approximately:
  • 211-375 million episodes annually
  • 73 million physician consultations
  • 1.8 million hospitalizations
  • 3,100 deaths 1
• Highest disease incidence is among children under 5 years, but highest hospitalization and death rates occur in persons 65 years or older 1

Diagnostic Approach

The diagnostic approach to diarrhea depends on its duration and severity:

• Acute diarrhea: Usually infectious and self-limiting; diagnostic tests generally limited to severe cases 4, 5
• Chronic diarrhea: Requires more extensive evaluation including stool studies, endoscopy, imaging, and possibly biopsy 1, 3

Management Principles

Management of diarrhea follows these general principles:

• Rehydration: Oral rehydration whenever possible is the cornerstone of treatment 1, 5
• Dietary management: Early oral refeeding is recommended 5
• Symptomatic treatment: Antimotility agents like loperamide may be used for watery diarrhea but should be avoided in bloody diarrhea 1, 5
• Antimicrobial therapy: Selectively used for specific infectious causes 1
• Probiotics: May shorten the duration of illness in some cases 5

Common Pitfalls and Caveats

• Avoid antimotility agents in patients with bloody diarrhea or proven infection with Shiga toxin-producing E. coli 1
• Recognize that passage of formed stools, even if frequent, does not constitute diarrhea 1
• Be aware that functional disorders like irritable bowel syndrome may overlap with chronic diarrhea definitions 1
• Consider that normal-appearing stools with streaks of blood on toilet paper may represent hemorrhoids rather than dysentery 1