What imaging study should be ordered first when interstitial lung disease is suspected?

Imaging for Suspected Interstitial Lung Disease

When ILD is suspected, high-resolution CT (HRCT) of the chest is the primary imaging modality and should be ordered, with chest radiography serving only a complementary role to exclude alternative diagnoses. 1

Initial Imaging Approach

HRCT Chest (Primary Modality)

HRCT chest is the gold standard for diagnosing ILD and often provides a definitive diagnosis, obviating the need for surgical biopsy. 1

• HRCT demonstrates superior sensitivity (95.7%) and specificity (63.8%) compared to all other imaging modalities for detecting ILD 1
• HRCT findings are sufficient to permit either a limited differential or confident single diagnosis in most cases 1
• A negative chest HRCT is useful in excluding disease 1
• HRCT correlates with physiologic testing and provides prognostic value 1

Technical Specifications for HRCT

The HRCT protocol should include thin-section images (<1.5 mm slice thickness), inspiratory prone images to differentiate dependent atelectasis from early fibrosis, and supine end-expiratory imaging to assess for air-trapping. 1

• Volumetric CT data acquisition with thin-section multiplanar reconstructions aids evaluation of ILD distribution 1
• Low-dose chest CT without contrast is adequate for ILD assessment 1
• IV contrast serves no purpose in suspected ILD, though it may help identify non-pulmonary manifestations or alternative diagnoses 1

Critical caveat: CT angiogram studies are often inadequate for ILD assessment because they are typically performed in incomplete inspiration, which may produce marked atelectasis that can obscure, accentuate, or mimic ILD. 1

Role of Chest Radiography

Chest radiography should NOT be used as the primary screening tool for ILD due to low sensitivity (58-64%) and nonspecific patterns. 1

• Chest radiography serves a complementary role by excluding alternative diagnoses such as infectious pneumonia or pulmonary edema 1
• When ILD is suspected on radiographs, HRCT plays the central role in imaging diagnosis, not only characterizing true lung disease but also increasing specificity by identifying false-positives 1

Combined HRCT and Pulmonary Function Tests

For patients at increased risk of developing ILD (such as those with systemic autoimmune rheumatic diseases), screening with both HRCT chest and PFTs is conditionally recommended over PFTs alone. 1

• PFTs alone may be insufficient to detect ILD: FVC <80% has only 47.5% sensitivity compared to HRCT's 100% sensitivity 1
• Patients with ILD can have normal PFTs or difficulty performing PFTs due to cough or microstomia 1
• HRCT and PFTs provide complementary information: HRCT shows presence and pattern of ILD while PFTs demonstrate physiologic impact 1

Modalities NOT Recommended for Initial Imaging

MRI Chest

There is limited research supporting MRI use in ILD, and it is NOT recommended for initial imaging. 1

• While select fast MRI sequences have approached CT image quality in specific contexts (e.g., progressive massive fibrosis in pneumoconiosis), MRI has not been adequately studied for general ILD evaluation 1

FDG-PET/CT

There is no relevant literature supporting FDG-PET/CT for initial imaging evaluation of suspected ILD. 1

• Limited research suggests FDG-PET/CT may have a secondary role in specific ILDs (primarily sarcoidosis) for assessing disease severity and prognosis, but not for initial diagnosis 1

High-Risk Populations Requiring Screening

Patients with systemic autoimmune rheumatic diseases warrant proactive HRCT screening, as nearly 20% of ILDs are associated with autoimmune rheumatic diseases. 2

• Systemic sclerosis patients have approximately 50% prevalence of ILD and should receive baseline HRCT 2, 3
• Patients with anti-Scl-70 antibodies, diffuse cutaneous disease, or abnormal baseline PFTs should receive immediate HRCT 3
• Annual HRCT is advised for the first 3-4 years in patients with SSc phenotypes or risk factors for ILD 3
• Rheumatoid arthritis, Sjögren syndrome, mixed connective tissue disease, and idiopathic inflammatory myopathies all have significant ILD prevalence 2

Clinical Indicators Prompting HRCT

'Velcro' crackles on lung auscultation (69% sensitive, 66% specific) suggest lung fibrosis and should prompt HRCT evaluation even if respiratory symptoms are minimal. 1, 2

• Decreased diffusing capacity for carbon monoxide (DLCO) aids early diagnosis and warrants HRCT 2
• Irreversible loss of lung function can be silent and significant in early stages, making early HRCT detection essential for improved prognosis 2