Arielle
  • Etymology:
    Derived from “idio-” meaning “unknown” and “pulmonary fibrosis,” referring to scarring of lung tissue. The term highlights the absence of a known cause.
  • AKA:
    Cryptogenic Fibrosing Alveolitis (historical term).
  • What is it?
    IPF is a chronic, progressive, and fibrosing interstitial lung disease of unknown cause, primarily affecting older adults. It is characterized by the usual interstitial pneumonia (UIP) pattern on imaging and histology.
  • Caused by:
    1. Unknown etiology (Idiopathic).
    2. Risk Factors:
      • Genetic predisposition (e.g., mutations in surfactant protein or telomerase genes).
      • Environmental exposures (e.g., smoking, metal dust, or wood dust).
      • Chronic micro-injuries to alveolar epithelium triggering abnormal repair responses.
  • Resulting in:
    • Progressive fibrosis of the interstitial lung tissue.
    • Loss of alveolar architecture.
    • Decline in lung function with impaired gas exchange.
  • Why Subpleural?
    • Subpleural areas are subjected to greater mechanical strain during respiration, making them vulnerable to repetitive micro-injuries.
    • Thinner connective tissue and reduced vascular supply in the subpleural regions impair normal repair mechanisms.
    • Fibrosis tends to progress outward from the periphery toward the central lung parenchyma.
  • Why Basilar?
    • The lower lung regions experience more repetitive alveolar stretch and shear forces due to gravity-dependent ventilation and perfusion patterns.
    • Fibrosis typically progresses from the lung bases upward due to biomechanical and inflammatory factors.
  • Structural Changes:
    • Patchy fibrosis and remodeling of lung parenchyma.
    • Honeycombing (clusters of air-filled cystic spaces).
    • Subpleural and basal predominance of fibrotic changes.
  • Pathophysiology:
    • Persistent epithelial cell injury and abnormal repair lead to excessive fibroblast proliferation and extracellular matrix deposition.
    • Fibrotic areas progressively replace normal lung parenchyma, reducing compliance and impairing oxygen diffusion.
  • Pathology:
    • Gross: Firm, shrunken lungs with fibrosis, predominantly in the lower lobes.
    • Microscopic: Usual interstitial pneumonia (UIP) pattern, with:
      • Patchy interstitial fibrosis.
      • Temporal heterogeneity (areas of active fibrosis alongside older fibrotic areas).
      • Honeycombing and fibroblastic foci.
  • Association of IPF and UIP:
    • IPF is specifically defined by the presence of the UIP pattern on histology or high-resolution CT (HRCT).
    • UIP features include patchy fibrosis, temporal heterogeneity, honeycombing, and traction bronchiectasis.
    • While UIP can occur in other diseases (e.g., connective tissue diseases, asbestosis), IPF is idiopathic and requires exclusion of other causes.
  • Association with Collagen Vascular Diseases:
    • Collagen vascular diseases (CVDs) such as rheumatoid arthritis (RA) and systemic sclerosis (SSc) can present with UIP patterns similar to IPF.
    • CVD-associated ILD often responds better to immunosuppressive therapy than IPF.
    • Common associations include:
      • Rheumatoid arthritis (RA): UIP is the most common ILD pattern in RA-associated ILD.
      • Systemic sclerosis (SSc): Presents with either UIP or nonspecific interstitial pneumonia (NSIP).
  • Diagnosis:
    • Clinical presentation (progressive dyspnea, dry cough, older adults).
    • Exclusion of other causes of interstitial lung disease (e.g., autoimmune diseases).
    • High-resolution CT (HRCT) showing UIP pattern.
    • Lung biopsy may be needed if imaging is inconclusive.
  • Clinical:
    • Symptoms: Progressive dyspnea on exertion, persistent dry cough, fatigue, and weight loss.
    • Signs: Bibasilar inspiratory crackles (“Velcro crackles”), clubbing of fingers (in some cases).
  • Radiology:
    • CXR:
      • Findings: Reticulonodular opacities, particularly in the lower lung zones.
      • Associated Findings: Volume loss, especially in the lower lobes.
    • HRCT:
      • Parts: Predominantly involves subpleural and basal regions.
      • Size: Honeycomb cysts vary in size, often >2 mm.
      • Shape: Reticular lines and cystic spaces forming honeycombing.
      • Position: Subpleural and basal predominance.
      • Character: UIP pattern with no ground-glass opacities unless during acute exacerbation.
      • Time: Progressive over months to years.
      • Associated Findings: Traction bronchiectasis, architectural distortion.
  • Pulmonary Function Tests (PFTs):
    • Restrictive pattern with reduced forced vital capacity (FVC) and total lung capacity (TLC).
    • Diffusing capacity of the lungs for carbon monoxide (DLCO) is markedly reduced.
  • Management:
    • Pharmacologic:
      • Antifibrotic agents (e.g., pirfenidone, nintedanib) to slow disease progression.
    • Supportive care:
      • Oxygen therapy for hypoxemia.
      • Pulmonary rehabilitation to improve exercise capacity.
    • Advanced therapy:
      • Lung transplantation for eligible patients with severe disease.
    • Monitoring: Regular assessment with PFTs and imaging to track disease progression.
  • Recommendations:
    • Early referral to a pulmonologist for suspected IPF.
    • Smoking cessation and avoidance of lung irritants.
    • Vaccinations (influenza, pneumococcal) to prevent infections.
  • Key Points and Pearls:
    • IPF is the most common idiopathic interstitial lung disease, primarily affecting older adults.
    • The UIP pattern on HRCT is diagnostic and may obviate the need for a biopsy.
    • Antifibrotic therapy can slow progression but does not reverse fibrosis.
    • Acute exacerbations of IPF are life-threatening and require urgent medical attention.

 

References and Links

Attili, A.K etal  Smoking-related Interstitial Lung Disease: Radiologic-Clinical-Pathologic Correlation RadioGraphics Vol. 28, No. 5

Gupta et al Diffuse Cystic Lung Disease: Part I  American Journal of Respiratory and Critical Care Medicine 191(12)  April 2015

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