In a patient over 40 with suspected diverticulitis, how should I confirm the diagnosis and what are the first‑line treatment options for uncomplicated versus complicated disease?

Diagnosis and Management of Diverticulitis in Patients Over 40

Diagnostic Confirmation

CT abdomen and pelvis with IV contrast is the gold standard for confirming diverticulitis, achieving 95-99% sensitivity and 96-99% specificity, and should be obtained in all patients without a prior imaging-confirmed diagnosis. 1

When to Image

• Obtain CT in patients presenting with left lower quadrant pain, fever, or leukocytosis to confirm diagnosis, as clinical assessment alone is correct in only 40-65% of cases 1
• Image all patients with severe presentations, immunocompromised status, failure to improve with therapy, or multiple recurrences to evaluate for complications 1
• CT is mandatory in elderly patients (>65 years) as only 50% present with typical lower quadrant pain, only 17% have fever, and 43% lack leukocytosis 1

CT Protocol and Alternatives

• IV contrast is preferred to characterize bowel wall abnormalities and detect complications like abscess, though unenhanced CT is acceptable if contrast is contraindicated 1
• Ultrasound may be used as an alternative in patients with contrast allergy or severe renal disease, though it is operator-dependent with lower specificity (90%) compared to CT 1
• MRI has high sensitivity but lower specificity and is rarely feasible in acute settings 1

Critical Pitfall

Do not rely on inflammatory markers alone to exclude complicated disease—up to 39% of patients with complicated diverticulitis have CRP <175 mg/L 1

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First-Line Treatment: Uncomplicated Diverticulitis

Antibiotics can be selectively avoided in immunocompetent patients with mild uncomplicated diverticulitis (no abscess, perforation, or systemic sepsis), as they do not accelerate recovery or prevent complications. 1

Outpatient Management Without Antibiotics

• Reserve observation alone for immunocompetent patients with uncomplicated disease (WSES stage 0), no systemic symptoms, and ability to tolerate oral intake 1
• Recommend clear liquid diet during acute phase advancing as symptoms improve, typically over 3-5 days 1
• Provide pain control with acetaminophen rather than NSAIDs 2

When Antibiotics Are Mandatory

Treat with antibiotics if any of the following are present: 1, 2

• Systemic symptoms: persistent fever, chills, or vomiting
• Laboratory markers: CRP >140 mg/L or WBC >15 × 10⁹/L
• High-risk patients: age >80 years, immunocompromised (chemotherapy, steroids, transplant), pregnant, or significant comorbidities (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes)
• CT findings: fluid collection, longer segment of inflammation (>86 mm), or pericolic air/fluid (WSES stage 1a)
• Symptom duration >5 days before presentation

Antibiotic Regimens for Uncomplicated Disease

Outpatient oral therapy (4-7 days): 1, 2

• First-line: Amoxicillin-clavulanate 625 mg three times daily OR
• Alternative: Ciprofloxacin 500 mg twice daily PLUS metronidazole 500 mg three times daily

Inpatient IV therapy (if unable to tolerate oral): 2

• Ceftriaxone 1-2 g daily PLUS metronidazole 500 mg three times daily OR
• Ampicillin-sulbactam 3 g every 6 hours

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First-Line Treatment: Complicated Diverticulitis

All patients with complicated diverticulitis require broad-spectrum IV antibiotics and risk-stratified interventions based on CT findings. 1, 2

WSES Stage 1b-2a: Abscess Present

Initiate IV antibiotics immediately: 2

• Ceftriaxone 1-2 g daily PLUS metronidazole 500 mg three times daily OR
• Piperacillin-tazobactam 3.375-4.5 g every 6-8 hours

Percutaneous CT-guided drainage is indicated for abscesses ≥3-4 cm 1, 2

WSES Stage 3-4: Generalized Peritonitis or Free Perforation

Emergent laparotomy with colonic resection is mandatory—this is not optional 1, 2

• Mortality for emergent surgery is 10.6% versus 0.5% for elective resection 2
• Do not attempt non-operative management in patients with feculent peritonitis, hemodynamic instability, or distant free air 1

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Post-Acute Management

Colonoscopy Timing

Perform colonoscopy 6-8 weeks after symptom resolution (or longer if symptoms persist) in the following scenarios: 1

• All patients with complicated diverticulitis (7.9% cancer risk)
• First episode of uncomplicated diverticulitis unless high-quality colonoscopy performed within 1 year (1.3% cancer risk)
• Sooner if alarm symptoms present: change in stool caliber, iron deficiency anemia, rectal bleeding, or unintentional weight loss 1

Critical Pitfall

Do not perform colonoscopy during acute inflammation—wait minimum 6-8 weeks to reduce perforation risk 1