What are the possible diagnoses and treatments for abdominal pain and diarrhea?

Differential Diagnosis and Management of Abdominal Pain with Diarrhea

Most Likely Diagnoses

For acute presentations (symptoms <14 days), viral gastroenteritis is the most common etiology and requires only supportive care, while bacterial causes should be considered if fever >38.5°C, bloody stools, or severe symptoms are present. 1, 2

Acute Infectious Causes (<14 days duration)

• Viral gastroenteritis (most common): Self-limited, typically resolves within 3-7 days without specific treatment 2
• Bacterial gastroenteritis: Consider if high fever (≥38.5°C), bloody diarrhea, recent travel, or signs of sepsis are present 1
• Parasitic infections: Suspect with prolonged symptoms, travel history, or endemic area exposure 1

Non-Infectious Causes (especially if symptoms ≥14 days)

• Irritable Bowel Syndrome (IBS): Characterized by recurrent abdominal pain with altered bowel habits, bloating, and mucus passage without structural abnormality 1, 3
• Inflammatory Bowel Disease (IBD): Consider with weight loss, bloody diarrhea, persistent symptoms, or family history 1
• Celiac disease: Should be excluded before diagnosing IBS 3
• Lactose intolerance: Consider in patients not responding to initial therapy 1

Initial Diagnostic Approach

When to Perform Laboratory Testing

Routine stool cultures and laboratory workup are NOT recommended for most patients with acute watery diarrhea. 1, 2

Order diagnostic testing ONLY if:

• Severe dehydration or illness present 2
• Persistent fever documented in medical setting 1
• Bloody stools 1
• Immunocompromised status 1
• Symptoms lasting ≥14 days 1
• Age >50 years (colonoscopy for cancer screening) 1
• Recent international travel with fever ≥38.5°C 1

Recommended Initial Tests (when indicated)

• Screening tests: Stool hemoccult and complete blood count 1
• Additional tests based on clinical features: Sedimentation rate (especially in younger patients), serum chemistries and albumin, stool for ova and parasites 1
• For persistent symptoms: Consider lactose breath test, celiac serologies, or colonoscopy with biopsies for microscopic colitis 1

Treatment Algorithm

First-Line Management: Rehydration and Symptomatic Relief

Oral rehydration solution (ORS) is the first-line therapy for mild to moderate dehydration, with reduced osmolarity ORS being most effective. 1, 4

Rehydration Protocol

• Mild to moderate dehydration in adults: ORS 2-4 L over 3-4 hours 1
• Replacement during maintenance: Ad libitum up to ~2 L/day, continuing as long as diarrhea persists 1
• Nasogastric administration: Consider if patient cannot tolerate oral intake 1

Symptomatic Treatment for Non-Bloody Diarrhea

Loperamide (2-4 mg up to four times daily) is effective for reducing loose stools, urgency, and fecal soiling, but must be avoided in bloody diarrhea or suspected STEC infection. 3, 5

Critical contraindications for loperamide:

• Bloody diarrhea 5
• Suspected STEC infection 1
• Pediatric patients <2 years of age 5
• Patients with fever and signs of invasive bacterial infection 1

For abdominal pain/cramping:

• Antispasmodics (dicyclomine 10-20 mg before meals or hyoscyamine 0.125-0.25 mg sublingual as needed): Effective for postprandial cramping 3, 6
• Peppermint oil: Alternative first-line option with direct smooth muscle relaxant properties 3, 6

When to Use Empiric Antibiotics

Empiric antimicrobial therapy is NOT recommended for most immunocompetent patients with acute watery diarrhea. 1

Exceptions requiring empiric antibiotics:

• Infants <3 months with suspected bacterial etiology 1
• Documented fever in medical setting + abdominal pain + bloody diarrhea + bacillary dysentery (presumed Shigella) 1
• Recent international travel with temperature ≥38.5°C or signs of sepsis 1
• Immunocompromised patients with severe illness and bloody diarrhea 1

Empiric antibiotic choices:

• Adults: Fluoroquinolone (ciprofloxacin) OR azithromycin, depending on local resistance patterns and travel history 1
• Children: Third-generation cephalosporin (infants <3 months or neurologic involvement) OR azithromycin 1

Management of Persistent Symptoms (≥14 days)

For symptoms lasting 14 days or more, consider non-infectious etiologies including IBS and IBD, and avoid empiric antimicrobial therapy. 1

IBS-Specific Treatment (if diagnosed)

First-line therapies:

• Loperamide for diarrhea control (titrate carefully to avoid constipation) 3
• Antispasmodics for abdominal pain, particularly postprandial 3
• Soluble fiber (ispaghula/psyllium 3-4 g/day, gradually increased) for global symptoms 3
• Regular exercise 3

Second-line therapies (if first-line fails after 3-6 weeks):

• Tricyclic antidepressants (amitriptyline starting 10 mg once daily, titrate to 30-50 mg): Effective for global symptoms and abdominal pain 3
• 5-HT3 receptor antagonists (ondansetron 4 mg once daily, titrate to maximum 8 mg three times daily): For diarrhea-predominant symptoms 3
• Low FODMAP diet: Supervised by trained dietitian with gradual reintroduction 3

Critical Pitfalls to Avoid

• Never use loperamide in bloody diarrhea or suspected STEC infection due to risk of hemolytic uremic syndrome 1, 5
• Avoid routine stool cultures in uncomplicated acute watery diarrhea without alarm features 1, 2
• Do not prescribe antibiotics empirically for simple acute watery diarrhea in immunocompetent patients 1
• Avoid insoluble fiber (wheat bran) in IBS as it may exacerbate symptoms 3
• Do not use antispasmodics indefinitely without reassessment after 3-6 weeks 6
• Exclude celiac disease before diagnosing IBS 3
• Reassess patients not responding to initial therapy for non-infectious causes including lactose intolerance, IBD, or bile acid malabsorption 1