Interstitial Lung Diseases

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ILD Basics - The Lung's Labyrinth

  • Definition: Diverse group of diffuse parenchymal lung diseases (DPLDs) primarily affecting the interstitium - the tissue space between alveolar epithelium and capillary endothelium, including basement membrane, perivascular, and perilymphatic tissues.
  • Common Pathological Features: Varying degrees of inflammation and fibrosis of the pulmonary interstitium.
  • Major Categories:
    • Idiopathic Interstitial Pneumonias (IIPs) (e.g., IPF)
    • ILD of known cause (e.g., CTD, drug, occupational pneumoconioses)
    • Granulomatous ILDs (e.g., Sarcoidosis, Hypersensitivity Pneumonitis)
    • Other rare ILDs Normal vs. Acute Phase Alveolar Changes in ILD

⭐ Idiopathic Pulmonary Fibrosis (IPF) is the most common and has the worst prognosis among IIPs.

IIPs Deep Dive - Mysterious Mists

IIPKey HistologyHRCT FindingsPrognosis
IPF (UIP)Temporal & spatial heterogeneity, fibroblastic fociBasal, subpleural predominant honeycombing, traction bronchiectasisPoor (median survival 2-5 yrs)
NSIPCellular/fibrotic (temporally uniform inflammation/fibrosis)Bilateral, symmetric GGO; fine reticulation; subpleural sparingVariable, better than IPF
COP (BOOP)Masson bodies (intraluminal organizing PNA plugs)Patchy, peripheral/peribronchial consolidations; GGOsGood, steroid-responsive
AIP (Hamman-Rich)Diffuse Alveolar Damage (DAD) - hyaline membranesDiffuse, bilateral GGOs and/or consolidations, rapid progressionVery poor, high acute mortality

Classification of Interstitial Lung Diseases (ILDs)

⭐ Cryptogenic Organizing Pneumonia (COP) often presents with flu-like symptoms and shows excellent response to corticosteroids.

Secondary ILDs - Environmental & Autoimmune Invaders

  • Pneumoconioses: Chronic mineral dust inhalation.
    DiseaseAgentOccupationKey PathologyCXR/CT Finding
    SilicosisSilicaMining, SandblastingSilicotic nodules, ↑TB riskApical "rock-like" nodules, Eggshell calcification (hilar)
    CWPCoalCoal miningCoal macules, Progressive Massive Fibrosis (PMF)-
    AsbestosisAsbestosShipbuilding, InsulationAsbestos bodies, Pleural plaquesBasal fibrosis, ↑Mesothelioma risk
    BerylliosisBerylliumAerospace, ElectronicsNon-caseating granulomasHilar lymphadenopathy
    Microscopic views of asbestos bodies in lung tissue
  • Hypersensitivity Pneumonitis (HP): Immune reaction to inhaled organic antigens (Farmer's, Bird fancier's lung).
    • Acute: Neutrophils.
    • Chronic: Lymphocytes, granulomas, fibrosis.
  • Drug-induced ILD: Amiodarone, Bleomycin, Methotrexate. Patterns: pneumonitis, fibrosis.
  • ILD in Connective Tissue Diseases (CTD): RA, Scleroderma (NSIP common), SLE.

⭐ Asbestosis: ↑ risk of lung cancer (esp. smokers) & primary cause of mesothelioma.

Sarcoidosis Focus - Granuloma Galaxy

  • Definition: Multisystem granulomatous disorder of unknown etiology, characterized by immune cell accumulation.
  • Pathology: Hallmark is non-caseating epithelioid granulomas.
    • May contain Schaumann bodies (laminated calcium concretions) or Asteroid bodies (stellate inclusions). Non-caseating epithelioid granuloma in sarcoidosis
  • Pulmonary: Bilateral hilar lymphadenopathy (BHL) is classic. Also, pulmonary infiltrates, fibrosis. Chest X-ray: Bilateral hilar lymphadenopathy in sarcoidosis
    • Lofgren's syndrome: Acute BHL, erythema nodosum, fever, arthralgia.
  • Extrapulmonary: Skin (erythema nodosum, lupus pernio), eyes (uveitis), heart, nervous system.
  • Labs: Elevated serum Angiotensin-Converting Enzyme (ACE) levels (↑~60% cases), hypercalcemia.

⭐ Bilateral hilar lymphadenopathy (BHL) is the most common radiographic finding in pulmonary sarcoidosis.

ILD Diagnosis - Detective's Toolkit

  • Clinical: Progressive dyspnea, non-productive cough, bibasilar crackles.
  • PFTs: Restrictive pattern: ↓TLC, ↓FVC, ↓DLCO; FEV1/FVC normal or ↑.
  • HRCT Chest: Key! Patterns: Ground-glass opacity (GGO), reticular, honeycombing (UIP), traction bronchiectasis. Ground glass vs. Consolidation
  • Biopsy: Transbronchial, cryobiopsy, or surgical (SLB) if diagnosis uncertain. Multidisciplinary discussion (MDD) vital.

⭐ Honeycombing on HRCT, often bibasilar and subpleural, is a hallmark of Usual Interstitial Pneumonia (UIP) pattern and indicates advanced fibrosis.

High‑Yield Points - ⚡ Biggest Takeaways

  • Idiopathic Pulmonary Fibrosis (IPF) typically presents with a UIP pattern on histology and honeycomb lung on HRCT; prognosis is poor.
  • Sarcoidosis is characterized by non-caseating granulomas, bilateral hilar lymphadenopathy, and often elevated serum ACE levels.
  • Hypersensitivity Pneumonitis results from an immune reaction to inhaled organic antigens (e.g., Farmer's lung, Bird fancier's lung).
  • Pneumoconioses are caused by inorganic dust inhalation; key examples include silicosis (eggshell calcification, ↑TB risk) and asbestosis (pleural plaques, ↑mesothelioma risk).
  • Many drugs can induce ILD, notably amiodarone, bleomycin, and methotrexate.
  • Connective tissue diseases such as rheumatoid arthritis and scleroderma are frequently associated with ILD development.
  • Smoking-related ILDs include respiratory bronchiolitis-ILD (RB-ILD) and desquamative interstitial pneumonia (DIP), primarily affecting smokers.

Practice Questions: Interstitial Lung Diseases

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Which of the following is not an obstructive lung disease?

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Flashcards: Interstitial Lung Diseases

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_____ bodies are seen in cryptogenic organizing pneumonia.

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_____ bodies are seen in cryptogenic organizing pneumonia.

Masson

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