Interstitial Lung Disease

Aka: Interstitial Lung Disease, Interstitial Pulmonary Disease, Diffuse Parenchymal Lung Diseases

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II. Definitions

  1. Interstitial Lung Disease
    1. Chronic, nonmalignant, noninfectious diseases
    2. Lower respiratory tract disease
      1. Distal lung parenchyma disease
      2. Alveolar wall inflammation and derangement

III. Epidemiology: Demographic Breakdown

  1. Age 20 to 40 years
    1. Sarcoidosis
    2. Collagen Vascular Disease
    3. Eosinophilic Granuloma or Pulmonary Histiocytosis X
    4. Lymphangioleiomyomatosis
  2. Age over 40 years
    1. Idiopathic Pulmonary Fibrosis
  3. Female Predominance
    1. Collagen Vascular Disease
    2. Lymphangioleiomyomatosis
    3. Tuberous Sclerosis
  4. Male Predominance
    1. Pneumoconiosis (Asbestosis)
  5. Tobacco exposure
    1. More likely with Tobacco exposure
      1. Eosinophilic Granuloma or Pulmonary Histiocytosis X
      2. Respiratory Bronchiolitis (Smoker's Bronchiolitis)
      3. Diffuse Alveolar Hemorrhage: Goodpasture's Syndrome
    2. Less likely if Tobacco exposure
      1. Idiopathic Pulmonary Fibrosis
      2. Sarcoidosis
      3. Hypersensitivity Pneumonitis

IV. Causes (Mnemonic: DISCO)

  1. Drugs (See below)
  2. Idiopathic Pulmonary Fibrosis
  3. Sarcoidosis
  4. Collagen Vascular Disease
  5. Occupational Exposure
    1. Asbestos (e.g. Asbestosis)
    2. Fumes and gasses

V. Causes: Non-Granulomatous Causes

  1. Occupational Exposure
  2. Medications
    1. Antibiotics (e.g. Nitrofurantoin and GFR<30 ml/min)
    2. Chemotherapeutics (e.g. Methotrexate)
  3. Radiation
  4. Aspiration Pneumonia
  5. Post ARDS changes
  6. Idiopathic Pulmonary Fibrosis
  7. Collagen Vascular Disease
  8. Goodpasture's Syndrome
  9. Eosinophilic Pneumonia
  10. Amyloidosis
  11. Graft Versus Host Disease (Bone Marrow Transplant)

VI. Causes: Granulomatous Causes

  1. Hypersensitivity Pneumonitis (Organic dust)
  2. Inorganic dust (Beryllium silica)
  3. Sarcoidosis
  4. Langerhans Cell Granulomatosis
  5. Granulomatous Vasculitis
    1. Granulomatosis with Polyangiitis (previously known as Wegener's Granulomatosis)
    2. Allergic Granulomatosis of Churg-Strauss
    3. Lymphomatoid Granulomatosis
  6. Bronchocentric Granulomatosis

VII. Symptoms

  1. Historical data
    1. Complete occupational and environmental exposures
    2. Complete medication history
  2. Exertional Dyspnea
  3. Chronic Dyspnea
  4. Fatigue
  5. Malaise

VIII. Signs

  1. Inspiratory crackles (rales) at posterior lung bases
  2. Pulmonary Hypertension
  3. Fingernail Clubbing
    1. Suggests Idiopathic Pulmonary Fibrosis
    2. May suggest Bronchogenic Carcinoma

IX. Labs

  1. ACE Level is non-specific and not useful
  2. Erythrocyte Sedimentation Rate (ESR)
    1. Increased
  3. Complete Blood Count (CBC)
    1. Polycythemia (rare)
  4. Arterial Blood Gas (ABG)
    1. Hypoxemia

X. Diagnosis

  1. Pulmonary Function Tests
    1. Restrictive Lung Disease
    2. Reduced Total Lung Capacity
    3. DLCO decreased
  2. Bronchoalveolar Lavage
    1. Alveolar cells reflect type of inflammation

XI. Imaging: Diagnosis and Monitoring

  1. Chest XRay
    1. Lung parenchymal change (90%)
    2. Increased Interstitial Markings
    3. Non-resolving infiltrates
  2. Gallium Lung scanning
    1. Diffuse inflammation
  3. High Resolution Chest CT (preferred)
    1. Reticulated pattern (fine, net-like pattern of fibrosis)
    2. Honeycombing (thick walled, systic air spaces)
    3. Traction Bronchiectasis (airways distorted by scar tissue)
    4. Micronodules (small, inflammatory Nodules present in some ILD subtypes)
  4. CT Pulmonary Embolism
    1. Consider in ILD exacerbation (given higher PE Risk in this population)

XII. Differential Diagnosis

  1. See Dyspnea Causes
  2. Pneumonia and other lung infections
  3. Congestive Heart Failure
  4. Pulmonary Embolism
  5. Chronic Obstructive Pulmonary Disease

XIII. Management: ILD Exacerbation

  1. Precautions
    1. Consult pulmonology (or intensivist)
  2. Non-Invasive Positive Pressure Ventilation (BiPAP or HFNC)
    1. Have a low threshold to initiate early
    2. Endotracheal Intubation, in contrast, for ILD exacerbation has a very poor prognosis (90% mortality)
  3. Antibiotics
    1. Treat Community Acquired Pneumonia
    2. Consider treatment of PJP Pneumonia
  4. Corticosteroids
    1. Initial high dose Corticosteroids (start with 125 Methylprednisolone)
  5. Severe, end-stage progression
    1. Consider for lung transplant
    2. Consider ECMO bridging to transplant

XIV. References

  1. Long (2026) Interstitial Lung Disease, EM:Rap, accessed 5/18/2026

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