What is the most likely diagnosis and recommended evaluation and management for a 56‑year‑old man with diverticulosis, a urinary tract infection two months ago, hepatic steatosis, presenting with left lower quadrant abdominal pain radiating to the back?

Most Likely Diagnosis and Management

The most likely diagnosis is acute sigmoid diverticulitis, given the patient's age, known diverticulosis, and classic presentation of left lower quadrant pain radiating to the back. 1

Immediate Diagnostic Workup

Order a contrast-enhanced CT of the abdomen and pelvis immediately – this is the gold-standard test with 98-99% sensitivity and 99-100% specificity for confirming diverticulitis and detecting complications. 2, 1, 3 Clinical examination alone misdiagnoses 34-68% of cases, making imaging mandatory rather than optional. 2, 3

Laboratory Studies to Obtain Concurrently

• Complete blood count with differential (leukocytosis present in ~90% of cases) 1
• C-reactive protein (CRP >140-170 mg/L predicts complicated disease) 1
• Basic metabolic panel (assess renal function before contrast) 4

Risk Stratification Based on CT Findings

If CT Shows Uncomplicated Diverticulitis (No Abscess, Perforation, Fistula, or Obstruction)

For this immunocompetent 56-year-old male, observation without antibiotics is the first-line approach, supported by high-quality evidence from the DIABOLO trial (528 patients) showing antibiotics provide no benefit in uncomplicated cases. 1

Outpatient Management Criteria (All Must Be Met):

• Temperature <100.4°F (38°C) 1
• Pain controlled with acetaminophen alone (score <4/10) 1
• Ability to tolerate oral fluids and medications 1
• No significant comorbidities (his fatty liver alone does not preclude outpatient care) 1
• Adequate home support 1

Supportive Care Protocol:

• Clear liquid diet for 2-3 days, then advance as tolerated 1
• Acetaminophen 1g three times daily for pain (avoid NSAIDs) 1
• Adequate oral hydration 1

When to Add Antibiotics Despite Uncomplicated Disease:

Reserve antibiotics only if any of these high-risk features develop: 1

• Persistent fever >100.4°F or chills despite supportive care
• Refractory symptoms or vomiting
• Inability to maintain oral hydration
• CRP >140 mg/L or WBC >15 × 10⁹/L
• CT shows pericolic extraluminal air or fluid collection

If antibiotics become indicated:

• First-line oral regimen: Amoxicillin-clavulanate 875/125 mg twice daily for 4-7 days 1
• Alternative: Ciprofloxacin 500 mg twice daily + Metronidazole 500 mg three times daily for 4-7 days 1

If CT Shows Complicated Diverticulitis

Small Abscess (<4-5 cm):

• Hospital admission required 1
• IV antibiotics alone for 7 days (ceftriaxone + metronidazole OR piperacillin-tazobactam) 1
• No drainage needed 1

Large Abscess (≥4-5 cm):

• Hospital admission required 1
• CT-guided percutaneous drainage PLUS IV antibiotics 1
• Continue antibiotics for 4 days after successful drainage 1

Perforation with Peritonitis or Sepsis:

• Emergent surgical consultation for source control (Hartmann's procedure or primary resection with anastomosis) 1
• Broad-spectrum IV antibiotics immediately 1

Mandatory Follow-Up

Re-evaluate within 7 days (or sooner if symptoms worsen). 1 If symptoms persist beyond 5-7 days despite appropriate management, obtain repeat CT to assess for complications rather than simply extending therapy. 1

Post-Acute Management

Colonoscopy Timing:

Schedule colonoscopy 6-8 weeks after symptom resolution if: 1

• This is his first episode of diverticulitis
• He hasn't had high-quality colonoscopy in the past year
• He's ≥50 years (age-appropriate screening)
• CT showed any complicated features

Recurrence Prevention:

• High-fiber diet (≥22 g/day from fruits, vegetables, whole grains, legumes) 1
• Regular vigorous physical activity 1
• Maintain normal BMI (18-25 kg/m²) 1
• Smoking cessation 1
• Avoid NSAIDs when possible 1
• Do NOT restrict nuts, corn, popcorn, or seeds – this myth has been debunked 1, 4

Critical Pitfalls to Avoid

• Do not prescribe routine antibiotics for uncomplicated disease without high-risk features – this adds resistance without benefit 1
• Do not rely on clinical examination alone – imaging is mandatory because the classic triad (left lower quadrant pain, fever, leukocytosis) is present in only ~25% of cases 2, 3
• Do not perform colonoscopy during the acute phase – wait 6-8 weeks to avoid perforation risk 2, 3
• Do not assume his prior UTI is relevant unless he develops concurrent urinary symptoms suggesting colovesical fistula (a complication of diverticulitis) 2

Special Consideration for This Patient

His history of hepatic steatosis (fatty liver) does not change management unless he has cirrhosis with significant hepatic dysfunction, which would classify him as high-risk requiring antibiotics. 1 Simple steatosis alone does not preclude outpatient observation without antibiotics if CT confirms uncomplicated disease. 1