What is the appropriate evaluation and management for a 69-year-old patient presenting with new left lower-quadrant abdominal pain?

Evaluation and Management of Left Lower Quadrant Pain in a 69-Year-Old

Order CT abdomen and pelvis with IV contrast immediately—this is the single most accurate diagnostic test with 98% accuracy and is rated 8/9 (usually appropriate) by the American College of Radiology. 1

Initial Diagnostic Approach

Immediate Imaging is Essential

• CT with IV contrast is mandatory because clinical examination alone misdiagnoses 34-68% of cases, and the classic triad of left lower quadrant pain, fever, and leukocytosis occurs in only 25% of diverticulitis cases 2, 1
• CT identifies life-threatening complications (perforation, abscess, obstruction) that determine whether the patient requires emergency surgery, hospital admission with antibiotics, or outpatient management 2, 1
• In elderly patients (age 69), atypical presentations are common—only 50% have lower quadrant pain and only 17% have fever, making imaging even more critical 3

Laboratory Studies to Obtain Concurrently

• Complete blood count with differential (left shift >75% suggests bacterial infection) 1
• C-reactive protein (CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity) 1, 3
• Lactate level if the patient appears systemically ill 3

Most Likely Diagnosis and Key Differentials

Acute Sigmoid Diverticulitis (Most Common)

• Diverticulitis is the most common cause of left lower quadrant pain in adults over 50, with prevalence increasing 50% between 2000-2007 2, 4
• Approximately 10% of the Western population has diverticulosis at age 40, increasing to 70% in older patients, and 5-25% will develop diverticulitis 2

Critical Alternative Diagnoses That Cannot Be Missed

• Perforated colon cancer can mimic diverticulitis clinically and on CT—this is the most dangerous diagnosis to miss 1
  • CT features favoring cancer: pericolonic lymphadenopathy >1 cm in short-axis diameter 1
  • When lymphadenopathy is present with pericolonic edema, cancer must be excluded 1
• Large bowel obstruction from colorectal cancer or sigmoid volvulus (more common in elderly) 5
• Bowel ischemia (acute mesenteric ischemia or ischemic colitis)—much more common after age 80 5
• Pyelonephritis or nephrolithiasis 1
• Epiploic appendagitis 2
• Inflammatory bowel disease 2

Treatment Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, or Obstruction)

• Conservative management WITHOUT antibiotics is appropriate for immunocompetent patients 1, 3
• Antibiotics for maximum 7 days only if the patient is immunocompromised or elderly with high-risk features (though age 69 alone does not mandate antibiotics) 1, 3
  • Recommended regimen: Ertapenem 1 g q24h or Eravacycline 1 mg/kg q12h 1

Complicated Diverticulitis with Small Abscess (<4 cm)

• Antibiotics alone for 7 days without drainage 1, 3
• Use same antibiotic regimens as above 1

Complicated Diverticulitis with Large Abscess (≥4 cm)

• Percutaneous CT-guided drainage PLUS antibiotics for 4 days 1, 3
• Stop antibiotics at 4 days if source control is adequate and patient is immunocompetent 1

Perforation with Diffuse Peritonitis

• Emergency surgical consultation immediately for laparotomy with colonic resection 3
• Start broad-spectrum IV carbapenem therapy (Meropenem 1 g q6h by extended infusion, Doripenem 500 mg q8h, or Imipenem/cilastatin 500 mg q6h) 1

Critical Red Flags Requiring Emergency Surgery

• Free air on CT indicating perforation 1, 3
• Fecal peritonitis 3
• Signs of peritonitis on examination (diffuse tenderness, guarding, rebound, absent bowel sounds) 1
• Hemodynamic instability or septic shock 3

Special Considerations for This 69-Year-Old Patient

Age-Related Mortality Risk

• In-hospital mortality increases dramatically with age: 1.6% in patients <65 years, 9.7% in patients 65-79 years, and 17.8% in patients >80 years 3
• At age 69, this patient falls into the intermediate-risk category and warrants aggressive evaluation 3

Atypical Presentations in Elderly

• Do not rely on absence of fever or normal white blood cell count to rule out serious pathology—elderly patients frequently present without these classic findings 3, 5
• Gangrenous cholecystitis and complicated appendicitis occur more frequently in elderly due to delayed diagnosis 5

Common Pitfalls to Avoid

• Never assume diverticulitis based solely on history of diverticulosis—alternative pathologies, especially colon cancer, must be excluded with imaging 1
• Do not order plain radiographs as the initial test—they are insensitive and will delay definitive diagnosis 2
• Do not order ultrasound as the primary imaging modality for non-gynecologic left lower quadrant pain in this age group—it is operator-dependent and has limited utility 2, 6
• Do not perform routine colonoscopy after CT-confirmed uncomplicated diverticulitis unless age-appropriate screening is due, or CT shows abnormal lymph nodes, luminal mass, abscess, perforation, or fistula 2, 1

When to Repeat Imaging

• Obtain repeat CT if fever and leukocytosis persist beyond 48-72 hours despite appropriate treatment 1, 4
• Repeat imaging if clinical deterioration occurs at any point 3, 4
• If symptoms persist >2-3 days despite conservative outpatient management 1

Disposition Criteria

Safe for Outpatient Management

• Able to tolerate oral intake 1, 4
• No peritoneal signs on examination 1
• Reliable follow-up available 4
• Uncomplicated diverticulitis on CT 1

Requires Hospital Admission

• 83% of admitted patients are CT-positive, whereas 62.7% of discharged patients are CT-negative 7
• Only 7% of CT-negative patients require admission 7
• Presence of abscess, perforation, obstruction, or inability to tolerate oral intake 1, 3