emDOCs Podcast – Episode 129: Interstitial Lung Disease Part 1

What is ILD?

• Interstitial lung disease (ILD) is a group of conditions that result in chronic, restrictive lung physiology.
• Underlying pathophysiology includes infiltration of the alveoli with inflammatory cells and fibrotic changes occurring in the lung interstitium.
  • Pulmonary changes range from granulomatous inflammation without fibrosis to severe, diffuse parenchymal fibrosis and distortion of normal pulmonary architecture.
• Over 200 diseases/conditions associated with ILD: occupational or environmental agents, connective tissue disorders, sarcoidosis, and medication complications.
  • Idiopathic subtypes include idiopathic pulmonary fibrosis (IPF; one of the most severe subtypes), cryptogenic organizing pneumonia, idiopathic interstitial pneumonia.
• Severity based on patient symptoms, the subtype of ILD, CT findings, and pulmonary function testing.
• The severity of ILD is based on a variety of factors but patient symptoms, the subtype of ILD, CT findings, and pulmonary function testing are the primary determinants.
  • Mild or early disease, moderate, and advanced disease.
  • Progression from mild to moderate to severe respiratory symptoms and findings; rate of progression varies.

What are the incidence and prevalence?

• Incidence approximately 31.5 per 100,000 person-years in males and 26.1 per 100,000 person-years in females.
• Prevalence estimated at 80.9 per 100,000 in males and 67.2 per 100,000 in females.
• Chronic restrictive disease with recurrent exacerbations, which are responsible for over half of all inpatient admissions and over half of all deaths among patients with ILD.
  • 10-30% of patients have an acute exacerbation (AE-ILD) in the first two years after diagnosis.
  • Exacerbation more common in patients with advanced disease with worse pulmonary function and lower baseline oxygenation.
• Death in AE-ILD typically due to acute respiratory failure (ARF).

How do you define an exacerbation?

• AE-ILD: 1) known diagnosis of ILD; 2) worsening dyspnea in the last 30 days; 3) CT with new bilateral ground glass opacities and/or consolidation on a background of usual interstitial pneumonia; 4) deterioration not fully explained by fluid overload or heart failure.
• All four components required for the diagnosis, but if CT not available, then it is “suspected acute exacerbation”.
• Must exclude other issues/pathologies.

What are the triggers for AE-ILD?

• Infection the cause in 10-30% of AE-ILDs.
• Other triggers: air pollution, exacerbation of another condition (COPD or HF), pulmonary hypertension, microaspiration, pulmonary procedure (biopsy or bronchoscopy), VTE, medications.
  • Drug induced lung disease: pneumotox.com.
• 50% of acute exacerbations have no identified cause.

How do these patients present?

• Most commonly gradually worsening dyspnea with exertion and nonproductive cough.
• May also present with chest pain, hemoptysis, and wheezing
• Exam: crackles or velcro rales clubbing of the digits, and evidence of an underlying CTD.
• AE-ILD: worsening dyspnea and cough. May have fever and flu-like symptoms. Severe exacerbations present with hypoxemia and respiratory distress. Severity of hypoxemia is often disproportionate to dyspnea.

What’s the recommended testing?

• AE-ILD is a diagnosis of exclusion.
• Evaluate for alternate causes of respiratory decompensation. Patients with systemic autoimmune conditions may be on immunosuppressive regimens (risk of Pneumocystis jirovecii).
• Labs: CBC, renal and liver function, electrolytes, venous blood gas, troponin; respiratory viral panel can also be helpful.
• ECG
• Chest x-ray classically shows reticular pattern suggestive of interstitial lung disease; may see nodular or mixed patterns of alveolar filling and interstitial markings.
  • Dominant feature: peripheral reticular pattern.
  • Sensitivity of 80% and a specificity of 82% in diagnosing ILD.
• Outpatient testing: pulmonary function testing (DLCO, FVC, 6 minute walk test) and rheumatologic testing (CRP, ESR, antinuclear antibodies, rheumatoid factor, anti-cyclic citrullinated peptide)
• For AE-ILD, obtain high resolution chest CT (HRCT) with CTA of the chest; determine the type of lung opacities, evaluate for other complications/conditions (PE).
  • In AE-ILD, new bilateral ground glass opacities and/or consolidation on a background of reticular or honeycombing pattern.
  • ILD doubles the risk of VTE.
  • One potential issue: CTA can artificially make the ground-glass changes appear artificially worse. Combining CTA with high resolution CT slices can adjust for this artifact and evaluate for PE.
• POCUS: evaluate for RV strain, contractibility, effusion, and pneumothorax.

Summary:

• ILD is a chronic disease with restrictive lung physiology.
• Exacerbations are common and associated with severe morbidity and mortality.
• Patients present with hypoxemia and respiratory distress.
• Many different triggers of AE-ILD.
• Assess for other causes of the patient’s respiratory distress.
• HRCT and CTA of the chest are major parts of the ED evaluation for AE-ILD.

Stay tuned for Part 2, where we cover management of AE-ILD.