Diarrhea – In-Depth Clinical Lecture Notes
Definition
Diarrhea is defined as the passage of three or more abnormally loose or watery stools per day, reflecting increased stool frequency and/or volume. It represents a disturbance in intestinal water and electrolyte balance, impacting nutrient absorption and overall fluid homeostasis.
Classification
By Duration
- Acute: <14 days; mostly infectious origin
- Persistent: 14–30 days; mixed etiologies
- Chronic: >30 days; frequently noninfectious
By Mechanism
- Osmotic: Non-absorbed solutes (e.g., lactose intolerance)
- Secretory: Enterotoxin-induced water secretion (e.g., cholera)
- Exudative: Inflammatory damage & mucus/blood exudation (e.g., IBD)
- Motility-related: Rapid transit reduces absorption (e.g., IBS)
Etiology
Etiologies can be broadly divided into infectious and noninfectious causes:
Infectious Causes
- Bacteria: ETEC, Shigella, Salmonella, Campylobacter, C. difficile
- Viruses: Rotavirus, Norovirus, Adenovirus
- Parasites: Giardia lamblia, Entamoeba histolytica, Cryptosporidium
Non-Infectious Causes
- Malabsorption syndromes (lactose intolerance, celiac disease)
- Inflammatory bowel diseases (Crohn's disease, ulcerative colitis)
- Endocrine (hyperthyroidism, carcinoid syndrome, VIPoma)
- Medication-induced (laxatives, antibiotics)
- Neoplastic and radiation enteritis
Pathophysiology
- Osmotic Diarrhea: Retention of non-absorbable solutes leading to water retention in intestinal lumen.
- Secretory Diarrhea: Active secretion of electrolytes and water, often toxin-mediated.
- Exudative Diarrhea: Inflammatory destruction causes mucus, blood, and protein leakage.
- Motility Dysfunction: Accelerated transit time limits absorption.
Clinical Features
- Frequent loose or watery stools
- Abdominal cramps, urgency, bloating
- Signs of dehydration (dry mucosa, hypotension, tachycardia) in severe cases
- Fever and bloody stools suggest inflammatory or infectious etiology
- Weight loss and malnutrition if chronic
Diagnostic Approach
- Detailed History & Physical Examination
Assess onset, stool frequency/character, travel, diet, meds, systemic symptoms. - Laboratory Investigations:
- Stool microscopy for ova, cysts, leukocytes
- Stool cultures and toxin assays (e.g., C. difficile)
- Fecal leukocytes or lactoferrin (inflammation marker)
- Stool osmotic gap calculation:
Gap = 290 - 2 × (Na+ + K+) (mOsm/kg)
< 50: secretory diarrhea; > 100: osmotic diarrhea.
- Blood Tests: CBC, electrolytes, renal function, inflammatory markers (CRP, ESR)
- Endoscopy & Imaging: Colonoscopy with biopsy to evaluate for IBD, neoplasm.
- Specialized Tests: Breath tests (lactose intolerance), celiac serology.
Management Overview
1. General Supportive Measures
- Maintain hydration using Oral Rehydration Solutions (ORS)
- Implement dietary modifications: bland, low-residue foods; avoid lactose if intolerant
- Avoid antimotility agents in bloody diarrhea or suspected infection
- Correct electrolyte imbalances promptly
2. Etiology-Specific Therapies
- Antimicrobials: e.g., ciprofloxacin for bacterial infections; metronidazole for protozoal infections
- Anti-inflammatory: corticosteroids or immunomodulators for inflammatory bowel disease
- Discontinuation/substitution of offending medications (e.g., laxatives)
- Enzyme replacement therapy in pancreatic insufficiency
3. Adjunctive & Preventive Care
- Nutrition support in chronic or severe cases
- Patient education on hygiene, food safety, medication adherence
- Monitor and manage complications such as dehydration and malnutrition
Complications
- Severe dehydration → hypovolemic shock
- Electrolyte imbalances: hyponatremia, hypokalemia
- Malnutrition and weight loss (especially chronic diarrhea)
- Increased morbidity and mortality in pediatric and immunocompromised patients
Prognosis & Follow-up
Acute infectious diarrhea is usually self-limited with proper hydration and treatment. Chronic diarrhea requires multidisciplinary follow-up for underlying disease control, nutritional management, and monitoring of complications.
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