What is the diagnostic approach for interstitial lung disease?

Diagnosis of Interstitial Lung Disease

High-resolution computed tomography (HRCT) is the gold standard for diagnosing interstitial lung disease (ILD), and should be performed in all patients with suspected ILD, complemented by pulmonary function tests and multidisciplinary evaluation involving pulmonologists, radiologists, and pathologists. 1, 2

Diagnostic Approach

Initial Clinical Evaluation

• Assess for respiratory symptoms:
  • Dyspnea on exertion
  • Dry cough
  • Presence of 'velcro' crackles on auscultation (moderate sensitivity for early ILD) 1
• Evaluate for signs of underlying connective tissue disease:
  • Joint pain or swelling
  • Raynaud's phenomenon
  • Skin changes
  • Muscle weakness 2

Essential Diagnostic Tests

1. High-Resolution Computed Tomography (HRCT)

   • Gold standard imaging modality for ILD diagnosis 1, 2
   • Acquisition parameters:
     • Volumetric scan on full inspiration (slice thickness 1.5mm)
     • Additional acquisitions in ventral decubitus
     • Non-contiguous acquisition on expiration 1, 2
   • Can detect subclinical abnormalities and characterize ILD patterns:
     • UIP (Usual Interstitial Pneumonia) pattern: honeycombing, traction bronchiectasis, subpleural and basal reticulation 1
     • NSIP (Non-Specific Interstitial Pneumonia): ground-glass opacities with traction bronchiectasis 1

2. Pulmonary Function Tests (PFTs)

   • Reveal restrictive lung physiology and impaired gas exchange 1
   • Include:
     • Spirometry (FVC, FEV1/FVC ratio)
     • Total lung capacity (TLC)
     • Diffusing capacity (DLCO) 1, 2
   • Not specific enough for diagnosis but essential for monitoring disease progression 1

3. Laboratory Testing

   • Comprehensive autoantibody panel to identify underlying connective tissue diseases:
     • Antinuclear antibodies (ANA)
     • Rheumatoid factor (RF) and anti-CCP
     • Anti-Scl-70/topoisomerase-1
     • Anti-centromere
     • Anti-SSA/Ro and anti-SSB/La
     • Anti-synthetase antibodies
     • ANCA 2

4. Echocardiography

   • Recommended as part of initial evaluation to:
     • Rule out structural cardiovascular disease
     • Assess for pulmonary hypertension (associated with worse prognosis) 1

Additional Diagnostic Considerations

1. Surgical Lung Biopsy

   • Consider when HRCT findings are not typical of a specific ILD pattern 1
   • Decision to perform biopsy should be made during multidisciplinary discussion
   • Video-assisted surgical lung biopsy (VATS) is preferred 1
   • Consider risks based on patient age, comorbidities, and disease severity 1

2. Bronchoalveolar Lavage

   • Generally reserved for cases where:
     • First diagnostic impression is inconclusive
     • Infection or lung toxicity is suspected 1

Multidisciplinary Approach

A multidisciplinary discussion involving pulmonologists, radiologists, and pathologists experienced in ILD is essential for accurate diagnosis 1, 2. This approach:

• Integrates clinical, radiological, and pathological findings
• Increases diagnostic accuracy
• Is especially beneficial for complex cases 1

Disease Monitoring and Follow-up

High-Risk Patients

• PFTs every 6 months
• Annual HRCT for first 3-4 years 1, 2

Lower-Risk Patients

• Annual PFTs
• HRCT if symptoms worsen or PFTs decline 1, 2

Common Pitfalls to Avoid

1. Relying solely on symptoms for ILD detection (90% of RA-ILD patients may be asymptomatic) 1, 2

2. Overlooking subtle PFT abnormalities that may indicate early disease 2

3. Failing to consider underlying connective tissue diseases in patients presenting with ILD 2

4. Inadequate multidisciplinary collaboration, which is essential for accurate diagnosis 1

5. Delaying HRCT in high-risk patients, which can lead to delayed diagnosis and treatment 1, 2

By following this systematic diagnostic approach, clinicians can accurately diagnose ILD, determine its etiology, assess severity, and guide appropriate treatment decisions to improve patient outcomes.