What is the recommended initial imaging modality to evaluate a persistent cough?

Imaging Modality for Persistent Cough

Chest radiography (plain chest X-ray) is the recommended initial imaging modality for evaluating persistent cough, as endorsed by the American College of Chest Physicians (ACCP), American College of Radiology (ACR), and multiple pulmonary societies. 1, 2

Initial Imaging Approach

• Obtain a chest radiograph first in all patients with chronic cough (>8 weeks duration) as the mandatory first-line imaging test 1, 2, 3
• Chest radiography achieves diagnosis in 82-93% of cases when used as part of standardized clinical protocols 2
• This approach is cost-effective and has acceptable diagnostic yield for most common causes of chronic cough 1

When to Proceed to High-Resolution CT (HRCT)

HRCT should be reserved for specific clinical scenarios, not routinely ordered:

• Abnormal chest radiograph findings - proceed directly to HRCT without delay 1, 2, 4
• Failed empiric treatment - when initial clinical evaluation and sequential treatment for common causes (upper airway cough syndrome, asthma, GERD) have failed after 8+ weeks 1
• Red flag symptoms present, including:
  • Hemoptysis (especially in smokers) 1, 4
  • Smoker >45 years with new or changing cough pattern 2
  • Prominent dyspnea, hoarseness, or systemic symptoms 2
  • Recurrent pneumonia 2
  • Unexplained weight loss or fever 3

Critical Evidence on CT Utilization

The evidence strongly suggests against routine CT scanning in all chronic cough patients:

• Studies show that 266 out of 267 patients with chronic cough and normal chest X-rays were successfully managed clinically with minimal investigation, requiring CT in only 4 patients (1.5%) 1
• In a large cohort of 1,006 chronic cough patients with normal chest X-rays who underwent CT, only 0.8% had major findings (malignancy or infectious disease requiring immediate treatment) 5
• Wide application of chest CT in all patients with chronic cough is of low clinical yield and exposes patients to unnecessary radiation 1

Important Limitations of Chest Radiography

Be aware that chest X-rays miss certain conditions:

• Bronchiectasis is missed in 34% of cases (most common finding on CT in patients with normal X-rays at 28%) 1, 2, 6
• Bronchial wall thickening is missed in 21% of cases 2, 6
• Central airway tumors can be bronchoscopically visible but radiographically occult in 16% of cases 1, 4
• The negative predictive value of chest X-ray for pulmonary causes of chronic cough is only 64% 6

Special Consideration: Smokers with Hemoptysis

This population requires aggressive evaluation regardless of chest X-ray findings:

• Bronchoscopy is indicated even when chest radiograph is normal in smokers with persistent cough and hemoptysis 1, 4
• Central airway malignancies were found in 16% of patients with normal chest radiographs who had risk factors and symptoms suggestive of bronchogenic carcinoma 1
• Do not delay bronchoscopy based on a normal chest X-ray in this high-risk population 4

Modalities NOT Recommended for Initial Evaluation

• FDG-PET/CT: No relevant literature supports its use in initial chronic cough evaluation 1
• MRI chest: Not included in clinical algorithms by pulmonary societies; reserved for indeterminate findings on other modalities 1
• V/Q scan: No relevant literature supports its use for chronic cough evaluation 1

Practical Algorithm

1. Start with chest radiography in all patients with chronic cough >8 weeks 1, 2
2. If chest X-ray is abnormal → proceed immediately to HRCT 1, 2
3. If chest X-ray is normal → pursue clinical evaluation and empiric treatment for common causes (UACS, asthma, GERD) 1, 2
4. If symptoms persist despite 8+ weeks of appropriate empiric treatment → order HRCT 1
5. If red flags present (hemoptysis, smoking history, systemic symptoms) → order HRCT and/or bronchoscopy regardless of chest X-ray findings 1, 2, 4