Interstitial Lung Diseases

Interstitial Lung Diseases

Interstitial Lung Diseases

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ILD Overview & HRCT Patterns - Lungs in Distress

  • Interstitial Lung Disease (ILD): Heterogeneous group of disorders affecting lung interstitium, often leading to inflammation & fibrosis.

  • Broad Classification:

    • Known causes: Drugs (Amiodarone, Bleomycin), Connective Tissue Diseases (CTD - RA, SSc), Environmental (Silicosis, Asbestosis).
    • Idiopathic Interstitial Pneumonias (IIPs): e.g., Usual Interstitial Pneumonia (UIP), Non-Specific Interstitial Pneumonia (NSIP).
    • Granulomatous: Sarcoidosis, Hypersensitivity Pneumonitis (HP).
    • Rare ILDs: e.g., Lymphangioleiomyomatosis (LAM), Pulmonary Langerhans Cell Histiocytosis (PLCH).
  • Key HRCT Patterns:

    • Ground-Glass Opacity (GGO): Hazy ↑ lung density, vessels visible.
    • Reticular pattern: Network of fine lines.
    • Honeycombing: Clustered, stacked subpleural cysts (typically 3-10 mm diameter, <3 mm walls); key for UIP.
    • Nodules (distribution): Perilymphatic (Sarcoidosis, Silicosis), Centrilobular (HP, RB-ILD), Random (Miliary TB, fungal).
    • Traction bronchiectasis/bronchiolectasis: Irreversible airway dilatation due to adjacent fibrosis.
    • Consolidation; Cysts.
  • Distribution Patterns:

    • Apical: Silicosis, Sarcoidosis (chronic), PLCH, Ankylosing Spondylitis.
    • Basal & Peripheral: UIP/IPF, Asbestosis, most CTD-ILDs.

HRCT chest showing honeycombing and traction bronchiectasis

⭐ Honeycombing on HRCT is a hallmark of the Usual Interstitial Pneumonia (UIP) pattern, indicating irreversible fibrosis and generally associated with a poorer prognosis compared to other IIPs without honeycombing.

IIPs - The Usual Suspects

  • Idiopathic Pulmonary Fibrosis (IPF) / Usual Interstitial Pneumonia (UIP): Most common IIP, progressive, poor prognosis.

    • UIP Pattern (HRCT): Basal, subpleural, reticular pattern; honeycombing is hallmark. +/- traction bronchiectasis. Absence of features suggesting alternative diagnoses.
    • See flowchart for diagnostic categories (Definite, Probable, Indeterminate, Alternative Dx). image
  • Nonspecific Interstitial Pneumonia (NSIP): Better prognosis than IPF.

    • HRCT: Ground-glass opacities (GGO), reticulation, traction bronchiectasis. Typically basal predominant; subpleural sparing can occur.
    • Cellular (more GGO, better response) vs. Fibrotic.
  • UIP vs. NSIP Key Differences:

    FeatureUIP (IPF)NSIP
    DistributionBasal, subpleuralBasal (subpleural sparing possible)
    GGOMinimal/AbsentOften Prominent (esp. cellular)
    HoneycombingCommon, HallmarkRare/Absent
    PrognosisPoorBetter

⭐ Honeycombing on HRCT is the most specific finding for a UIP pattern.

  • Other Major IIPs: Cryptogenic Organizing Pneumonia (COP), Respiratory Bronchiolitis-ILD (RB-ILD), Desquamative Interstitial Pneumonia (DIP), Lymphocytic Interstitial Pneumonia (LIP), Acute Interstitial Pneumonia (AIP). 📌 Can Really Do Lung Assessment.

Sarcoid & HP - Granuloma Spotlight

  • Sarcoidosis: Multisystem granuloma; common thoracic involvement.

    • HRCT:
      • Perilymphatic nodules (along bronchovascular bundles, interlobular septa, subpleural regions).
      • Bilateral, symmetrical hilar/mediastinal lymphadenopathy (LAPs).
      • Fibrosis in later stages (upper/mid zone predominant).
    • Scadding Stages: 0 (Normal CXR) to IV (Pulmonary fibrosis).
    • 📌 Mnemonic: "1-2-3 sign" (Right paratracheal + bilateral hilar LAPs); perilymphatic "beading".
  • Hypersensitivity Pneumonitis (HP): Immune response to inhaled antigens.

    • HRCT:
      • Acute/Subacute: Centrilobular GGO nodules, mosaic attenuation (air trapping on expiration).
      • Chronic: Fibrosis (often mid/upper zone or diffuse), honeycombing (can mimic UIP but distribution differs), significant air trapping.

HRCT Sarcoidosis vs UIP

⭐ "Three-density pattern" ("headcheese sign": normal lung, GGO, air trapping) on HRCT strongly suggests subacute HP.

Pneumoconioses & CTD‑ILDs - Occupational & Systemic

  • Pneumoconioses: ILDs from inhaled inorganic dusts.
    • Silicosis: Upper lobe nodules, hilar eggshell calcification. Risk of Progressive Massive Fibrosis (PMF).
    • CWP: Similar to silicosis; simple vs. complicated (PMF).
    • Asbestosis: Lower lobe fibrosis, pleural plaques (parietal, diaphragmatic), benign effusions. Possible causes of pleural thickening
  • CTD-ILD: Systemic autoimmune disease-associated ILD.
    • Patterns:
      CTDCommon ILD Pattern(s)
      SclerodermaNSIP (most common)
      MyositisNSIP, OP
      RAUIP (most common)
      Sjögren'sLIP, NSIP

    ⭐ Asbestosis: only pneumoconiosis significantly ↑ mesothelioma risk, esp. in smokers.

High‑Yield Points - ⚡ Biggest Takeaways

  • UIP/IPF: Characterized by basal, subpleural honeycombing.
  • NSIP: Shows ground-glass opacities with subpleural sparing; linked to CTDs.
  • Sarcoidosis: Presents with bilateral hilar lymphadenopathy and upper lobe predominant reticulonodular patterns.
  • Silicosis/CWP: Features upper lobe nodules and eggshell calcification of hilar nodes.
  • HP: Key findings include centrilobular nodules, air trapping, and the headcheese sign.
  • LCH: Upper lobe cysts and nodules in smokers, typically spares costophrenic angles.
  • LAM: Diffuse thin-walled cysts in women of childbearing age; associated with tuberous sclerosis.

Practice Questions: Interstitial Lung Diseases

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Sarcoidosis is least likely to be associated with:

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Flashcards: Interstitial Lung Diseases

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_____ on HRCT is a sign of alveolitis signifying active and reversible stage of the disease.

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_____ on HRCT is a sign of alveolitis signifying active and reversible stage of the disease.

Ground glass haze

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