What are the diagnostic criteria for an active diverticulitis episode?

Diagnosing Active Diverticulitis

The diagnosis of active diverticulitis requires a combination of clinical assessment, laboratory markers, and radiological findings, as clinical examination alone is insufficient for accurate diagnosis. 1

Clinical Assessment

Key Clinical Features

• Left lower quadrant pain and tenderness (most common presentation)
• Fever
• Systemic symptoms: malaise
• Associated symptoms may include:
  • Anorexia
  • Constipation
  • Nausea
  • Diarrhea
  • Dysuria 2

Clinical Decision Rules

A clinical decision rule developed by Laméris et al. has shown high diagnostic accuracy (97% positive predictive value) when all three criteria are present:

1. Direct tenderness only in the left lower quadrant
2. CRP > 50 mg/L
3. Absence of vomiting 1

Similarly, Andeweg et al. identified independent predictors with 86% diagnostic accuracy:

• Age
• History of previous episodes
• Pain localized to lower left abdomen
• Pain aggravation with movement
• Absence of vomiting
• Tenderness in lower left abdomen
• CRP ≥ 50 mg/L 1, 3

Laboratory Evaluation

• C-reactive protein (CRP): Key inflammatory marker
  • CRP > 50 mg/L strongly suggests diverticulitis
  • CRP > 170 mg/L may differentiate severe from mild diverticulitis (87.5% sensitivity, 91.1% specificity) 1
• Complete blood count (elevated white blood cell count)
• Basic metabolic panel
• Urinalysis (to rule out urinary causes) 2

Imaging Studies

• CT scan: Gold standard for diagnosis
  • Sensitivity: 98%
  • Specificity: up to 99% 4
  • Key CT findings in uncomplicated diverticulitis:
    • Diverticula
    • Colonic wall thickening
    • Increased density of pericolic fat 1
  • Findings in complicated diverticulitis:
    • Pericolic air bubbles
    • Pericolic fluid
    • Abscess formation
    • Distant free gas 1

Classification of Diverticulitis

The WSES classification divides diverticulitis into:

1. Uncomplicated diverticulitis:

   • Inflammation limited to colon wall and surrounding tissue

2. Complicated diverticulitis:

   • Stage 1A: Pericolic air bubbles or small amount of fluid
   • Stage 1B: Abscess ≤ 4 cm
   • Stage 2A: Abscess > 4 cm
   • Stage 2B: Distant gas (> 5 cm from inflamed segment)
   • Stage 3: Diffuse fluid without distant free gas
   • Stage 4: Diffuse fluid with distant free gas 1

Common Pitfalls in Diagnosis

• Relying solely on clinical examination (insufficient accuracy)
• Failing to obtain appropriate imaging in moderate to severe cases
• Confusing with other conditions:
  • Appendicitis (especially with right-sided diverticulitis)
  • Inflammatory bowel disease
  • Ischemic colitis
  • Colorectal cancer 4

Diagnostic Algorithm

1. Assess clinical presentation (LLQ pain, fever, absence of vomiting)
2. Check inflammatory markers (CRP > 50 mg/L)
3. If clinical suspicion is high based on clinical decision rules, diagnosis is likely
4. For moderate to severe symptoms or diagnostic uncertainty, proceed to CT scan
5. Consider colonoscopy 4-6 weeks after resolution of symptoms to exclude alternative diagnoses (especially in complicated cases or patients >50 years without recent colonoscopy) 1, 2

Remember that while some patients with mild diverticulitis may be diagnosed clinically using decision rules, imaging significantly improves diagnostic accuracy and is essential for assessing complications that would alter management.