What is the best course of treatment for a 50-year-old female with a history of diverticulitis, presenting with intermittent left lower abdominal pain, bloating, gas, fever, and decreased appetite?

Differential Diagnosis: 50-Year-Old Female with History of Diverticulitis and Left Lower Abdominal Pain

This patient most likely has recurrent acute diverticulitis, but requires immediate CT imaging with IV contrast to distinguish between uncomplicated recurrence versus complicated disease (abscess, perforation, or other complications), as clinical symptoms alone are unreliable for diagnosis. 1, 2

Critical Initial Diagnostic Step

Obtain CT abdomen/pelvis with IV contrast immediately to establish the diagnosis and assess for complications. 1, 2 CT has 98-99% sensitivity and 99-100% specificity for acute diverticulitis and is essential for guiding treatment decisions. 3, 1

• If IV contrast is contraindicated, alternatives include ultrasound, MRI, or non-contrast CT 2
• The presence of fever makes complicated diverticulitis more likely and mandates imaging before treatment decisions 1

Key Differential Diagnoses to Consider

Primary Considerations:

• Recurrent acute diverticulitis (uncomplicated vs. complicated) - most likely given history and presentation 1, 3
• Diverticular abscess - suggested by fever and history of diverticulitis 4, 2
• Perforated diverticulitis with peritonitis - fever and tenderness raise this concern 4, 2

Important Alternative Diagnoses to Exclude:

• Colorectal malignancy - can mimic diverticulitis, especially with recurrent symptoms; 1.16% risk in diverticulitis patients 1
• Inflammatory bowel disease (Crohn's disease) - can present similarly with left-sided symptoms 1
• Ischemic colitis - particularly in patients with vascular risk factors 1
• Gynecologic pathology - ovarian cyst, tubo-ovarian abscess, or ectopic pregnancy in premenopausal women 5

Risk Stratification Based on Presentation

This patient has multiple high-risk features predicting complicated disease:

• Fever - indicates systemic inflammatory response 1, 3
• Decreased appetite and systemic symptoms - suggests more severe disease 1
• History of diverticulitis - recurrent episodes may have higher complication rates 1
• Alcohol consumption as trigger - may indicate more severe inflammation 1

Laboratory Studies to Obtain

• Complete blood count - assess for leukocytosis (WBC >15 × 10⁹ cells/L indicates need for antibiotics) 1
• C-reactive protein - CRP >140 mg/L predicts complicated disease and need for antibiotics 1, 3
• Basic metabolic panel - assess hydration status and renal function 6
• Urinalysis - exclude urinary tract infection as alternative diagnosis 6

Treatment Algorithm Based on CT Findings

If Uncomplicated Diverticulitis (No Abscess/Perforation):

Assess for antibiotic indications:

This patient requires antibiotics based on presence of fever, which indicates systemic inflammatory response. 1, 3

Additional indications present or to assess:

• Fever/chills (present) 1, 3
• Increasing leukocytosis (pending labs) 1
• CRP >140 mg/L (pending labs) 1
• Vomiting or inability to maintain hydration (assess) 1

Outpatient oral antibiotic regimen (if patient meets outpatient criteria):

• Amoxicillin-clavulanate 875/125 mg orally twice daily for 4-7 days 1, 3
• Alternative: Ciprofloxacin 500 mg twice daily PLUS metronidazole 500 mg three times daily for 4-7 days 1, 3

Outpatient criteria (all must be met):

• Temperature <100.4°F 1
• Able to tolerate oral fluids and medications 1, 2
• Pain controlled with acetaminophen alone 1
• No significant comorbidities or frailty 1
• Adequate home support 1

If outpatient criteria NOT met - hospitalize for:

• IV fluid resuscitation 3
• IV antibiotics: Ceftriaxone PLUS metronidazole OR Piperacillin-tazobactam 1, 3
• Transition to oral antibiotics as soon as patient tolerates oral intake 1

If Complicated Diverticulitis on CT:

Small abscess (<4 cm):

• IV antibiotics alone for 7 days 1
• Hospitalization required 2

Large abscess (≥4 cm):

• Percutaneous CT-guided drainage PLUS IV antibiotics 4, 1, 2
• Obtain cultures from drainage to guide antibiotic therapy 4, 2
• Antibiotic duration: 3-5 days after adequate source control 4, 2

Free air or diffuse peritonitis:

• Immediate surgical consultation - non-operative management contraindicated 2
• Emergent laparotomy with colonic resection 3
• Delay dramatically increases mortality 2

Supportive Care Measures

• Clear liquid diet during acute phase, advance as symptoms improve 1, 7
• Acetaminophen for pain control - avoid NSAIDs as they increase risk of complications 7, 1
• Avoid alcohol until resolution and completion of antibiotics (especially with metronidazole - disulfiram-like reaction) 1
• Bowel rest to minimize mechanical irritation 7, 3

Mandatory Follow-Up

• Re-evaluation within 7 days, earlier if clinical deterioration 1, 2
• Colonoscopy 6-8 weeks after symptom resolution to exclude malignancy (7.9% risk in complicated cases, 1.16% in uncomplicated) 1, 2

Critical Pitfalls to Avoid

• Do not treat empirically without CT imaging - clinical symptoms alone cannot distinguish uncomplicated from complicated disease 2
• Do not assume this is simple uncomplicated diverticulitis - fever indicates systemic involvement requiring antibiotics 1, 3
• Do not delay surgical consultation if free air or peritonitis present on CT 2
• Do not use NSAIDs for pain control - they increase risk of perforation and complications 7, 1
• Do not stop antibiotics early even if symptoms improve 1
• Do not skip follow-up colonoscopy - malignancy must be excluded 1, 2