General

• Essentially a large group of disorders that affect the alveolar wall that potentially leads to diffuse scarring and fibrosis
• Traditionally termed Interstitial Lung Disease however its a misnomer
• The interstitium formally refers only to the region of the alveolar wall exclusive of and separating the alveolar epithelial cells and capillary endothelial cells
• But interstitial lung diseases affect all components of the alveolar wall: epithelial cell, endothelial cell, and cellular and noncellular components of the interstitium
  • usually extends into the alveolar spaces so now its called diffuse parenchymal lung disease
• Idiopathic Interstitial Pneumonias
  • a group of pathologic entities that represent a subcategory of DPLD

Pathology

• Two major pathologic components that occur simultaneously
  • inflammatory process in the alveolar wall and alveolar spaces (sometimes called alveolitis)
  • scarring or fibrotic process
• Active inflammation is the primary process and fibrosis that follows is a secondary feature
  • Exception: Idiopathic Pulmonary Fibrosis in which the primary process is epithelial cell injury and fibrosis representing an abnormal repair of injury rather than alveolar inflammation
• Active alveolitis
  • Presence of a variety of inflammatory cells (macrophages, lymphocytes, neutrophils, eosinophils, and plasma cells) that infiltrate the alveolar wall
  • Types of DPLD may be a/w a prominence of a specific inflammatory cell type (e.g. eosinophils in Chronic Eosinophilic Pneumonia)
  • In addition to the presence of these inflammatory cells, other pathologic characteristics are useful in the diagnosis of a specific pathologic entity
    • For example: Granuloma
      • Granuloma typically also has multinucleated giant cells which result from the fusion of several phagocytic cells into a single large cell with abundant cytoplasm and many nuclei
      • Usually reflects an underlying immune process or reaction to a specific agent
      • DPLD with Granulomas = Sarcoidosis & Hypersensitivity Pneumonitis
        • Both have noncaseating granulomas

Pathology of Idiopathic Interstitial Pneumonias

• The term idiopathic indicates that a specific etiologic agent has not been identified for these disorders but we now know that smoking plays a contributory role or adds to the risk of developing several of the idiopathic interstitial pneumonia
• The terms used to describe the pathology and the associated clinical disorder may be different
• 
• Some of the pathologic patterns can be seen in lung disease a/w Connective Tissue Disease-Associated ILD
  • For example: NSIP (the pathologic pattern) when not idiopathic, can be a particularly common pathologic expression of pulmonary involvement in diseases such as Systemic Lupus Erythematosus, Rheumatoid Arthritis, and Systemic Sclerosis

• Pathology of Acute Lung Injury

  • Diffuse Alveolar Damage
  • Organizing Pneumonia

• Pathology of Chronic Fibrosing Interstitial Pneumonias

  • Usual Interstitial Pneumonia
  • Nonspecific Interstitial Pneumonia
  • Fibrotic Hypersensitivity Pneumonitis

• Pathology of Smoking Related Interstitial Pneumonias

  • Respiratory Bronchiolitis
    • • clinical features of interstitial lung disease = Respiratory Bronchiolitis-Associated ILD
    • • clinical features + fibrosis = Respiratory Bronchiolitis with Fibrosis
  • Desquamative Interstitial Pneumonia
    • Respiratory Bronchiolitis + clinical features of ILD + diffuse intrapulmonary spread
  • Langerhans Cell Histiocytosis

Pathology of Granulomatous Interstitial Lung Disease

• Pathology of Sarcoidosis

• Pathology of Nonfibrotic Hypersensitivity Pneumonitis

Pathogenesis

Pathophysiology

Clinical Features

Diagnostic Approach

Major Classification

1. Interstitial Lung Disease Associated with Systemic Inflammatory Disease

2. Idiopathic Interstitial Pneumonias

3. Granulomatous Interstitial Lung Disease

4. Diffuse Cystic Lung Diseases (DCLDs)

5. Iatrogenic Induced DPLD

6. Inorganic Causes of DPLD

7. Rare DPLD

Backlinks

• 02. Diseases of the Lung Parenchyma