For a patient with chronic cough, is a CT (Computed Tomography) scan with or without contrast recommended as the initial imaging study?

CT Without Contrast is Recommended for Chronic Cough Evaluation

For patients with chronic cough, a non-contrast CT chest should be performed only after initial chest radiography and when empiric treatment for common causes has failed, not as a routine first-line investigation. 1, 2

Initial Diagnostic Approach

• First-line imaging: Chest radiography (CXR) should be the initial imaging study for all patients with chronic cough 1, 2
• Initial evaluation: Should include:
  • Chest radiography
  • Pulmonary function testing
  • Empiric treatment for common causes (asthma, GERD, upper airway cough syndrome)

When to Consider CT Chest

CT chest should be considered only in specific scenarios:

1. Persistent symptoms despite optimal treatment for common causes
2. Abnormal chest radiograph requiring further characterization
3. Presence of red flag symptoms:
   • Hemoptysis
   • Weight loss
   • Fever
   • Recurrent pneumonia

Non-contrast vs. Contrast CT

• Non-contrast CT is generally sufficient for evaluation of chronic cough 1, 2
• The ACR Appropriateness Criteria specifically notes that "for the majority of studies, the noncontrast technique appears to be adequate" 1
• No high-quality studies have directly compared contrast-enhanced versus non-contrast CT for chronic cough evaluation 1

Evidence Supporting Limited Use of CT

• 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, 2
• A 2023 study found that among 1,006 chronic cough patients with normal chest X-rays who underwent CT scans, only 0.8% had major abnormal findings requiring immediate treatment decisions 3

Diagnostic Yield of CT After Normal CXR

• CT can reveal abnormalities not visible on chest radiography:
  • Bronchiectasis (found in 11.9% of patients with normal CXR) 4
  • Bronchial wall thickening (10.2%) 4
  • Mediastinal lymphadenopathy (8.5%) 4
• The negative predictive value of a normal chest radiograph for excluding pulmonary causes of chronic cough is only 64% 4

Clinical Pitfalls to Avoid

1. Overutilization of CT: Wide application of CT in all patients with chronic cough has low clinical yield and results in unnecessary radiation exposure 1, 2

2. Missing significant pathology: Relying solely on normal chest radiography may miss important findings - in one study, 36% of patients with normal CXR had relevant abnormalities on CT 4

3. Overinterpretation of incidental findings: CT frequently reveals minor abnormalities (36.5% in one study) that may not be clinically relevant to the cough 3

4. Delayed diagnosis: In rare cases, persistent cough despite normal CXR may be due to endobronchial lesions that require bronchoscopy rather than CT for diagnosis 5

In conclusion, while CT chest is an important diagnostic tool for chronic cough evaluation, it should be used selectively after initial chest radiography and when empiric treatment fails. When CT is indicated, non-contrast technique is generally sufficient unless there are specific concerns that would benefit from contrast enhancement.