What is the next step for a patient with prominent interstitial markings at the lung bases?

Management of Prominent Interstitial Markings at Lung Bases

The next step is to obtain high-resolution computed tomography (HRCT) of the chest to characterize the interstitial pattern and determine whether this represents early interstitial lung disease (ILD), interstitial lung abnormalities (ILAs), or a benign finding. 1

Initial Diagnostic Approach

HRCT Imaging is Mandatory

• HRCT is the essential next step to distinguish between various interstitial patterns and assess the extent and distribution of abnormalities 1
• Standard chest radiographs showing interstitial markings are insufficient for diagnosis and cannot reliably differentiate between various ILD patterns 1
• HRCT should be performed with:
  • Thin sections (≤2 mm slice thickness) 1
  • Both inspiratory and expiratory images 1
  • Prone positioning if gravity-dependent opacities are present 1
  • No contrast medium required 1

Clinical Context Assessment

While obtaining HRCT, simultaneously evaluate for:

• Respiratory symptoms: Progressive dyspnea, chronic cough, or exercise intolerance that would suggest clinically significant ILD rather than incidental findings 1
• Exposure history: Occupational exposures, environmental antigens (for hypersensitivity pneumonitis), smoking history, and medication review 1
• Systemic disease screening: Connective tissue disease symptoms, as organizing pneumonia and interstitial patterns can occur with polymyositis, antisynthetase syndrome, and other autoimmune conditions 1, 2

HRCT Pattern Recognition Determines Next Steps

If HRCT Shows Definite UIP Pattern

• Honeycombing with subpleural and basal predominant reticular opacities with traction bronchiectasis establishes UIP pattern and may be sufficient for IPF diagnosis if other causes are excluded 1
• No lung biopsy needed if clinical context supports IPF and HRCT shows definite UIP 1
• Proceed to pulmonary function testing (spirometry with DLCO) to assess severity 1

If HRCT Shows Possible UIP or Indeterminate Pattern

• Multidisciplinary discussion (MDD) involving pulmonologist, radiologist, and pathologist is required to determine if surgical lung biopsy is indicated 1
• Video-assisted surgical lung biopsy should be considered if:
  • Diagnosis remains uncertain after HRCT 1
  • Patient is surgical candidate with acceptable operative risk 1
  • Results would change management 1
• Biopsy should sample 2-3 lobes due to potential histologic discordance 1

If HRCT Shows Alternative Patterns

• Ground-glass opacities with mosaic attenuation and relative basilar sparing suggest hypersensitivity pneumonitis—pursue antigen identification and consider bronchoscopy with bronchoalveolar lavage 1
• Peribronchovascular distribution with ground-glass opacities suggests nonspecific interstitial pneumonia (NSIP)—intensify search for connective tissue disease or drug exposure 1
• Organizing pneumonia pattern—investigate infectious, drug-related, radiation, or autoimmune etiologies before diagnosing cryptogenic organizing pneumonia 1, 2

If HRCT Shows Minimal Changes (ILAs)

• Interstitial lung abnormalities (ILAs) are defined as affecting <5% of any lung zone without meeting criteria for ILD 1
• If asymptomatic with normal pulmonary function, surveillance HRCT at 1-2 years is reasonable 1
• Consider genetic testing if family history of pulmonary fibrosis exists, as 15-30% of first-degree relatives have ILAs 1

Common Pitfalls to Avoid

• Do not delay HRCT: Plain radiograph interstitial markings are nonspecific and can represent technical factors, atelectasis, or early disease 1, 3
• Do not assume benign finding without HRCT confirmation: Even subtle interstitial markings can represent early progressive ILD 1
• Do not order lung biopsy before HRCT: Imaging must guide biopsy decisions and sampling locations 1
• Do not miss hypersensitivity pneumonitis: This requires specific questioning about bird exposure, hot tubs, mold, and occupational antigens, as it can mimic other ILDs but has different treatment 1
• Do not forget drug-induced ILD: Review all medications including over-the-counter supplements, as many drugs cause interstitial pneumonitis 1

Additional Baseline Testing

Concurrent with HRCT, obtain:

• Pulmonary function tests (spirometry, lung volumes, DLCO) to assess physiologic impairment 1
• Six-minute walk test with oxygen saturation monitoring to assess functional capacity and gas exchange 1
• Autoimmune serologies if connective tissue disease suspected (ANA, RF, anti-CCP, myositis panel, antisynthetase antibodies) 1
• Complete blood count: Eosinophilia may suggest drug reaction, parasitic infection, or eosinophilic pneumonia 1