Diarrhea and Constipation¶
Chapter 49 | Part 2: Cardinal Manifestations and Presentation of Diseases
KEY CLINICAL POINTS¶
- Diarrhea is defined as increased stool frequency (>3 times/day) or loose stools, while constipation is characterized by infrequent ( ≤ 3 times/week) or difficult bowel movements.
- Acute diarrhea ( ≤ 4 weeks) is most commonly infectious (90%), while chronic diarrhea (>4 weeks) is predominantly noninfectious (e.g., IBS, celiac disease, motility disorders).
- Chronic constipation is often due to slow transit, outlet obstruction, or pelvic floor dysfunction, with ~25% of cases involving evacuation disorders.
- Key diagnostic tools include stool analysis, colonoscopy, anorectal manometry, and colonic transit studies for functional disorders.
- Management depends on etiology: rehydration for acute diarrhea, dietary/lifestyle modifications for chronic constipation, and targeted therapies (e.g., lubiprostone for slow transit, loperamide for secretory diarrhea).
1. DEFINITION & OVERVIEW¶
Diarrhea and constipation are common gastrointestinal disorders. Diarrhea is defined as passage of abnormally liquid or unformed stools at increased frequency (>3 times/day), while constipation is characterized by infrequent ( ≤ 3 times/week), difficult, or incomplete bowel movements. These conditions may be acute (<2 weeks), persistent (2–4 weeks), or chronic (>4 weeks).
Table 49-1: Normal Gastrointestinal Motility¶
| Anatomic Level | Function |
|---|---|
| Stomach and Small Bowel | Synchronized MMC in fasting; accommodation, trituration, mixing, transit |
| Ileal reservoir | Empties boluses; facilitates mixing, retention of residue |
| Colon | Irregular mixing, fermentation, absorption, transit |
| Cecum, ascending, transverse | Reservoirs |
| Descending colon | Conduit |
| Sigmoid/rectum | Volitional reservoir |
1.1 Pathophysiology¶
Diarrhea results from altered fluid/electrolyte transport, motility, or secretion. Constipation arises from slow colonic transit, outlet obstruction, or pelvic floor dysfunction. Secretory diarrhea (e.g., cholera) involves excessive fluid secretion, while osmotic diarrhea is due to undigested solutes drawing water into the lumen.
1.2 Clinical Spectrum¶
Diarrhea may be acute (infectious, drug-induced), persistent (IBS, celiac disease), or chronic (IBD, motility disorders). Constipation may be functional (slow transit, outlet obstruction) or secondary to medications, structural abnormalities, or systemic diseases.
2. EPIDEMIOLOGY¶
Worldwide, >1 billion individuals experience acute diarrhea annually, with ~500,000 deaths in children <5 years. Chronic constipation is common in developed countries, with ~8.8% prevalence in the U.S. Women are 1.5x more likely than men to have chronic constipation.
2.1 Risk Factors¶
Acute diarrhea: travel, poor sanitation, immunocompromised states. Chronic constipation: aging, low fiber diet, medications (opioids, anticholinergics), pelvic floor dysfunction.
2.2 Demographics¶
Acute diarrhea: 40% of U.S. travelers to endemic regions develop traveler’s diarrhea. Chronic constipation: 10–20% of adults in developed countries.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Infectious agents (bacteria, viruses, parasites) cause ~90% of acute diarrhea. Noninfectious causes include IBS, celiac disease, motility disorders, and medication side effects. Constipation arises from slow transit, outlet obstruction, or pelvic floor dysfunction.
Table 49-2: Acute Infectious Diarrhea Pathobiology¶
| Pathobiology/A gents | Incubation Period | Vomiting | Abdominal Pain | Fever | Diarrhea |
|---|---|---|---|---|---|
| Toxin producers (Preformed toxin) | 1–8 h | 3–4+ | 1–2+ | 0–1+ | 3–4+, watery |
| Toxin producers (Enterotoxin) | 8–72 h | 2–4+ | 1–2+ | 0–1+ | 3–4+, watery |
| Enteroadherent | 1–8 d | 0–1+ | 1–3+ | 0–2+ | 1–2+, watery, mushy |
| Invasive organisms (Minimal inflammation) | 1–3 d | 1–3+ | 2–3+ | 3–4+ | 1–3+, watery |
| Invasive organisms (Severe inflammation) | 12 h–8 d | 0–1+ | 3–4+ | 3–4+ | 1–2+, bloody |
3.1 Infectious Pathogens¶
Common pathogens: Norovirus, Rotavirus, Salmonella, Shigella, Campylobacter, Giardia. Pathophysiology: Toxin-mediated (e.g., cholera), inflammatory (e.g., dysentery), or osmotic (e.g., lactose intolerance).
3.2 Noninfectious Mechanisms¶
IBS, celiac disease, IBD, motility disorders (slow transit, dyssynergia), drug-induced (opioids, anticholinergics), and structural abnormalities (rectal cancer, Hirschsprung’s disease).
4. CLINICAL FEATURES¶
Acute diarrhea: watery stools, fever, vomiting, abdominal pain. Chronic diarrhea: weight loss, steatorrhea, malabsorption. Constipation: infrequent stools, straining, hard stools, sense of incomplete evacuation.
4.1 Acute Diarrhea¶
Common features: profuse watery stools, fever, vomiting. Severe cases may present with dehydration, hypokalemia, or shock. Bloody stools suggest invasive pathogens (Shigella, E. histolytica).
4.2 Chronic Constipation¶
Features: infrequent bowel movements, straining, hard stools, bloating. May be associated with rectal pain, fecal impaction, or pelvic floor dysfunction.
5. DIFFERENTIAL DIAGNOSIS¶
Acute diarrhea: infectious agents, IBS, celiac disease, drug-induced. Chronic constipation: IBS, IBD, Hirschsprung’s disease, pelvic floor dysfunction, medications.
5.1 Acute Diarrhea¶
Differential diagnoses include viral gastroenteritis, bacterial infections (Salmonella, Shigella), parasitic infections (Giardia), and drug-induced (laxative abuse).
5.2 Chronic Constipation¶
Differential diagnoses include IBS, IBD, celiac disease, hypothyroidism, and structural abnormalities (rectal cancer, Hirschsprung’s disease).
6. INVESTIGATIONS & DIAGNOSIS¶
Stool analysis (microscopy, culture, PCR), colonoscopy, anorectal manometry, colonic transit studies, and imaging (CT, MRI) for structural abnormalities.
Table 49-3: Major Causes of Chronic Diarrhea¶
| Pathophysiology | Causes |
|---|---|
| Secretory | Bile acid malabsorption, IBS, celiac disease |
| Osmotic | Lactose intolerance, fructose malabsorption |
| Steatorrheic | Pancreatic insufficiency, celiac disease |
| Inflammatory | IBD, microscopic colitis |
| Dysmotile | IBS, pelvic floor dysfunction |
6.1 Stool Tests¶
Stool for leukocytes, calprotectin, parasites, bacterial toxins (C. difficile), and fat content. PCR for viral pathogens (Rotavirus, Norovirus).
6.2 Imaging¶
Colonoscopy for structural abnormalities (cancer, strictures). Radiopaque marker transit studies for colonic motility assessment.
7. MANAGEMENT & TREATMENT¶
Acute diarrhea: rehydration, antimotility agents (loperamide), antibiotics for bacterial infections. Chronic constipation: dietary fiber, osmotic laxatives, stool softeners, and enemas for fecal impaction.
Table 49-5: Causes of Constipation in Adults¶
| Type of Constipation | Examples |
|---|---|
| Recent Onset | Colonic obstruction (neoplasm, stricture), anal fissure, medications |
| Chronic | IBS, slow transit, pelvic floor dysfunction, hypothyroidism |
7.1 Acute Diarrhea¶
Oral rehydration with electrolyte solutions. Avoid loperamide in bloody diarrhea. Empirical antibiotics for travelers’ diarrhea (azithromycin, ciprofloxacin).
7.2 Chronic Constipation¶
Dietary fiber (15–25 g/day), osmotic laxatives (polyethylene glycol), and stool softeners. Biofeedback therapy for dyssynergia. Surgical options for outlet obstruction.
8. PROGNOSIS & COMPLICATIONS¶
Acute diarrhea: usually self-limiting, but may lead to dehydration. Chronic constipation: may cause fecal impaction, bowel obstruction, or rectal prolapse. Severe cases may require surgery.
8.1 Complications¶
Dehydration, electrolyte imbalances, malnutrition, fecal impaction, and bowel obstruction. Chronic constipation may lead to rectal prolapse or hemorrhoids.
8.2 Prognosis¶
Acute diarrhea: excellent with rehydration. Chronic constipation: variable, with long-term management required for functional disorders.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: avoid certain laxatives (senna). Pediatrics: manage dehydration carefully. Elderly: monitor for drug interactions and electrolyte imbalances. Immunocompromised: avoid self-medication with antibiotics.
9.1 Pregnancy¶
Avoid stimulant laxatives (senna). Use osmotic agents (polyethylene glycol) for constipation.
9.2 Elderly¶
Monitor for drug interactions (e.g., opioids, anticholinergics). Use stool softeners to prevent fecal impaction.
10. KEY POINTS & CLINICAL PEARLS¶
- Acute diarrhea in travelers is often due to E. coli, Salmonella, or Giardia. 2. Chronic constipation is often functional, managed with fiber and laxatives. 3. Secretory diarrhea is treated with bile acid sequestrants. 4. Evacuation disorders require biofeedback therapy. 5. Avoid loperamide in bloody diarrhea or IBS.