What are the criteria for diagnosing pseudomembranous colitis?

Criteria for Diagnosing Pseudomembranous Colitis

Pseudomembranous colitis is primarily diagnosed by the endoscopic finding of pseudomembranes on the colonic mucosa, which is caused by Clostridium difficile in the vast majority of cases and may suffice for diagnosis in the absence of another obvious cause. 1

Diagnostic Criteria

Clinical Presentation

• Diarrhea: Loose stools (Bristol stool chart types 5-7) with frequency perceived as too high by the patient 1
• Ileus: Signs of severely disturbed bowel passage (vomiting, absence of stool) with radiological signs of bowel distension 1
• Toxic megacolon: Radiological signs of colonic distension with severe systemic inflammatory response 1
• Fecal incontinence may be present as part of the disease 1
• Abdominal pain, cramping, and low-grade fever are common symptoms 2

Laboratory Findings

• Microbiological evidence of toxin-producing C. difficile in stools 1
• Marked leukocytosis (leukocyte count > 15 × 10^9/L) 1
• Marked left shift (band neutrophils > 20% of leukocytes) 1
• Rise in serum creatinine (>50% above baseline) 1
• Elevated serum lactate 1
• Hypoalbuminemia (<25 g/L) has been associated with high mortality and refractoriness to therapy 1

Endoscopic Findings

• Pseudomembranes: Yellow-white plaques on the mucosal surface of the colon 3
• Other findings such as edema, erythema, friability, and ulceration may be present, though their correlation with disease severity is unclear 1

Imaging Findings

• Distension of large intestine 1
• Colonic wall thickening including low-attenuation mural thickening 1
• Pericolonic fat stranding 1
• Ascites not explained by other causes 1

Diagnostic Testing Algorithm

1. Clinical Assessment:

   • Evaluate for compatible clinical picture (diarrhea, ileus, or toxic megacolon) 1
   • Rule out other causes of symptoms 1

2. Laboratory Testing:

   • Stool testing for C. difficile toxins A and B using enzyme immunoassays (sensitivity 50-80%, specificity 98-99%) 1
   • Testing for C. difficile common antigen (GDH) (sensitivity 85-95%, specificity 89-99%) 1
   • Real-time PCR assays for toxin B gene (sensitivity 97%, specificity 93%) 1
   • Two-step testing protocol recommended: first step using GDH, toxin EIA, or molecular test for TcdB; second step using method to detect free fecal toxins or GDH/toxin genes 4

3. Endoscopic Evaluation:

   • Sigmoidoscopy or colonoscopy to visualize pseudomembranes 1
   • Caution: Endoscopy is contraindicated in severe colitis due to risk of perforation or hemorrhage 1

4. Imaging:

   • Abdominal imaging to assess for colonic distension, wall thickening, and complications 1

Important Considerations

Markers of Severe Disease

• Leukocytosis > 15 × 10^9/L 1
• Elevated serum creatinine (>50% above baseline) 1
• Elevated serum lactate 1
• Fever (core body temperature > 38.5°C) 1
• Hemodynamic instability including signs of distributive shock 1
• Signs of peritonitis or ileus 1

Prognostic Factors

• Advanced age (≥65 years) 1
• Serious comorbidity and ICU admission 1
• Immunodeficiency 1
• Fecal incontinence has been linked to higher chance of recurrence 1
• Endoscopic finding of pseudomembranous colitis associated with higher recurrence risk 1
• Longer cumulative duration of previous episodes of CDI 1

Common Pitfalls

• Not all pseudomembranous colitis is caused by C. difficile; other pathogens, ischemia, and medications can cause similar findings 3
• Negative C. difficile testing or failure to improve on treatment should prompt evaluation for other causes 3
• Testing should only be performed on unformed stools from symptomatic patients with clinically significant diarrhea and no obvious alternative explanation 4
• Processing a single specimen at onset of symptoms is sufficient; multiple testing increases false-positive results 1
• In neutropenic patients, leukocytosis cannot be used as a criterion for disease severity 1

Treatment Response Criteria

• Decrease in stool frequency or improvement in stool consistency 1
• Improvement in parameters of disease severity (clinical, laboratory, radiological) 1
• No new signs of severe disease 1
• Response should be evaluated after at least 3 days of treatment 1
• Treatment with metronidazole may result in clinical response only after 3-5 days 1

By following these criteria and diagnostic approach, clinicians can accurately diagnose pseudomembranous colitis and initiate appropriate treatment to reduce morbidity and mortality associated with this condition.