What is diverticulitis in adults over 40 with a history of diverticulosis?

What is Diverticulitis?

Diverticulitis is inflammation and/or infection of diverticula (abnormal outpouchings in the colon wall), occurring in approximately 5-10% of adults with diverticulosis, particularly those over 40 years of age. 1, 2

Pathophysiology and Development

Diverticulitis results from microscopic or macroscopic perforation of a diverticulum due to diverticular inflammation and focal necrosis. 1 The condition develops when pre-existing diverticula—which are present in diverticulosis—become inflamed or infected, transforming an otherwise asymptomatic structural abnormality into an acute clinical problem. 1, 3

Epidemiology in Adults Over 40

• The prevalence increases dramatically with age, rising from 10% in patients under 50 years to 33% in those aged 60-69 years. 1
• Annual incidence in the United States is approximately 180 per 100,000 persons, resulting in over 200,000 hospitalizations annually with costs exceeding $6-8 billion. 1, 3, 2
• In Western populations, 90% of cases involve left-sided (sigmoid) diverticulitis, whereas Asian and African populations more commonly develop right-sided disease. 1
• Among patients with diverticulosis, approximately 5-10% will develop acute diverticulitis in their lifetime. 1, 3, 2

Clinical Classification

Uncomplicated Diverticulitis (85-88% of cases)

• Involves localized inflammation with colon wall thickening and peri-colonic inflammatory changes. 3, 2
• No abscess, perforation, fistula, or obstruction present. 1, 2

Complicated Diverticulitis (12-15% of cases)

• Associated with abscess formation, phlegmon, fistula, obstruction, bleeding, or perforation. 1, 2
• Requires more aggressive management including possible surgical intervention. 2

Clinical Presentation

The hallmark symptom is acute or subacute left lower quadrant abdominal pain (in left-sided disease), typically accompanied by: 3

• Fever and chills 3
• Changes in bowel habits (often constipation) 3
• Nausea and vomiting 3
• Elevated white blood cell count and/or C-reactive protein 3

Important caveat: In elderly patients over 65 years, the presentation may be more subtle—only 50% present with typical lower quadrant pain, 17% have fever, and 43% lack leukocytosis. 1 This atypical presentation can delay diagnosis in older adults.

Diagnostic Approach

• CT scan with IV contrast is the gold standard, with sensitivity of 98-99% and specificity of 99-100%. 4, 3, 2
• CT findings typically show colon wall thickening (>4mm) and increased density of pericolic fat. 3, 5
• The American College of Physicians recommends CT imaging when there is diagnostic uncertainty in suspected cases. 1
• Ultrasound can be useful in younger patients to avoid radiation exposure and in elderly patients who cannot undergo CT, though it is operator-dependent. 1

Risk Factors in Adults Over 40

Beyond age itself, several modifiable and non-modifiable factors increase risk: 1, 2

• Genetic factors (variants in TNFSF15 gene) 2
• Lifestyle factors: obesity (BMI ≥30), physical inactivity, smoking 1, 2
• Medications: NSAIDs (except aspirin for cardiovascular prevention), opioids, steroids 1, 2
• Comorbidities: hypertension, type 2 diabetes, connective tissue disorders 2
• Poor diet quality (low fiber intake) 1

Natural History and Prognosis

• The risk of complicated diverticulitis is highest with the first presentation. 1, 3
• Recurrence rates are 22% after an index episode and 55% after a second episode at 10-year follow-up. 1
• Mortality for elective surgical management is 0.5%, but rises to 10.6% for emergent surgery. 2
• In elderly patients, in-hospital mortality is higher (1.6% in those <65 years vs. 17.8% in those >80 years), though this relates more to comorbidities than age itself. 1

Key Clinical Pitfall

Colon malignancy can mimic diverticulitis on imaging. 1 While certain CT features help differentiate the two (preserved bowel wall layers in diverticulitis vs. disrupted layers in cancer), colonoscopy is often necessary after resolution of acute inflammation to exclude malignancy, particularly in patients without recent colonoscopy or with atypical features. 1, 5