Should a CT chest with or without contrast be ordered to investigate a chronic cough?

CT Chest Without Contrast is Preferred for Chronic Cough Evaluation When Indicated

CT chest without contrast should be performed only in selected patients with chronic cough who have red flag symptoms or persistent symptoms despite optimal treatment, not as a routine initial investigation. 1, 2

Initial Evaluation Algorithm

1. First-line investigation:

   • Chest radiography (CXR)
   • Pulmonary function testing

2. When to proceed to CT chest:

   • Red flag symptoms present (fever, weight loss, hemoptysis, recurrent pneumonia)
   • Persistent symptoms despite optimal treatment
   • Abnormal chest radiograph requiring further characterization

Evidence for Non-Contrast CT

The evidence does not support routine use of contrast for CT chest in chronic cough evaluation:

• No studies have directly compared contrast-enhanced versus non-contrast CT imaging for chronic cough 1
• For most evaluations of chronic cough, non-contrast technique appears adequate 1
• Contrast-enhanced studies offer improved visualization of cardiopulmonary vasculature and mediastinal structures, but these are rarely the primary concern in chronic cough evaluation 1

Clinical Yield of CT in Chronic Cough

CT can reveal abnormalities not visible on chest radiography:

• In patients with normal chest radiographs and chronic cough, CT revealed relevant abnormalities in 36% of cases 3
• Most common findings were bronchiectasis (11.9%), bronchial wall thickening (10.2%), and mediastinal lymphadenopathy (8.5%) 3
• The negative predictive value of chest radiography for excluding pulmonary causes of chronic cough is only 64% 3

However, CT should not be used routinely:

• In prospective studies, 74 out of 81 patients with chronic cough were successfully managed without CT examination 1
• In a retrospective cohort of patients with normal chest radiographs, only 4 out of 266 patients required CT for diagnosis (bronchiectasis, pulmonary fibrosis, and malignancy) 1

Common Findings on CT in Chronic Cough

When CT is performed, the following findings may be relevant:

• Bronchiectasis (most common finding)
• Bronchial wall thickening
• Interstitial lung disease patterns
• Small airways abnormalities
• Mediastinal lymphadenopathy

Pitfalls to Avoid

1. Overutilization of CT:

   • Wide application of CT in all patients with chronic cough has low clinical yield 1
   • Unnecessary radiation exposure
   • Potential for incidental findings leading to additional testing

2. Underutilization of CT:

   • Delaying CT in patients with red flags or persistent symptoms
   • Relying solely on normal chest radiography (which has a 36% false negative rate for relevant abnormalities) 3

3. Inappropriate use of contrast:

   • For most chronic cough evaluations, non-contrast CT is sufficient
   • Reserve contrast for specific concerns about vascular or mediastinal pathology

In summary, while CT chest is more sensitive than chest radiography for detecting abnormalities that may cause chronic cough, it should be used selectively based on clinical presentation and initial test results. When indicated, non-contrast CT is generally sufficient unless there are specific concerns that would benefit from contrast enhancement.