L29 Diffuse parenchymal lung disease (part I)

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L29 Diffuse parenchymal lung disease (part I)
2013-02-20 22:38:03
Pulmonary II

Diffuse parenchymal lung disease (part I)
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  1. Basic alveolar anatomy

    • Type I pneumocytes
    • ->95% of alveolar surface area
    • -thin, limited organelles
    • -minority of alveolar cell population (?)
    • -primary role: gas exchange
    • -some ion exchange, regulation of fluid
    • -susceptible to injury
    • -unable to replicate

    • Type II pneumocytes
    • -Cuboidal
    • -Majority of alveolar cell population (?)
    • -primary role: surfactant production, fluid balance, stem cells for type I
    • -lamellar bodies
    • -replicate on demand
    • -differentiate to replace injured type I cells
  2. Gas exchange
    • 1. Diffusion gradient from alveolus to capillaries
    • -PAO2 = FiO2*(Patm - PH2O) - (PaCO2/RQ)

    • 2. Time for diffusion
    • -typically requires ~0.25 seconds
    • -capillary travel time ~0.75 seconds

    • 3. Alterations of parenchyma have variable effects on oxygenation
    • -increased diffusion time (typically insignificant; time remains below 0.75sec)
    • -V/Q mismatching (always important)
  3. Diffuse parenchymal lung disease
    general characteristics
    • Destruction and distortion of the parenchymal anatomy
    • Thickening of alveolar/capillary interface
    • infiltration with immune cells
    • alveolar filling
    • bronchialar destruction or narrowing
    • granulomas
    • fibroblastic foci
    • traction bronchiectasis
    • fibrosis and honeycombing
  4. Diffuse parenchymal lung disease
    • Autoimmune disease
    • inhaled toxins or particulates
    • drug-induced
    • radiation-induced
    • hormonal contributions
    • associations with smoking
    • idiopathic
    • "classic" CT for parenchymal disease
    • (i.e. pulmonary fibrosis)
    • -some cystic changes
    • -honeycombing
    • -ground glass
  5. Compliance
    • Compliance is the change in volume for a given change in pressure
    • C=ΔV/ΔP
    • parenchymal lung disease decreases lung compliance
    • increased effort (pressure) to fill lung to same volume --> Sx
  6. Diffuse parenchymal lung disease
    general symptoms and findings
    • -Dry cough
    • -Shortness of breath
    • -Shallow breathing
    • -Swelling in ankles (R heart failure)
    • -Syncope
    • -asymptomatic (incidental finding on CXR)
    • -Acute respiratory decompensation

    • Exam findings:
    • -Dry crackles ("Velcro" crackles)
    • -Clubbing
    • -Enhanced or split P2
    • -Hypoxemia (especially with exertion)
    • -Cachexia --increased work of breathing
    • -Rheumatologic findings (arthritis, dermatitis, myositis, joint deformities)
  7. Pulmonary Function
    in diffuse parenchymal lung disease
    • May find restrictive, obstructive, or combined pattern
    • -Restriction is the most common pattern

    • Reduced DLCO "out of proportion" with volumes
    • -i.e. vital capacity ~70%, and DLCO ~30%

    may find hypocapnia and hypoxemia

    • Oxygen deseaturation with exertion is very common
    • -V/Q mismatching
    • -+/- impaired diffusion
  8. Pneumoconioses
    Chronic inhalation of small particulates that deposit into smallest airways, alveoli

    Disease is caused by immune system reaction to the accumulated particulates (i.e. alveolar macrophages)

    • Tx: Avoidance, protective equipment
    • -most industries now regulate exposure and require protective equipment

    **Predisposition for pulmonary infections, especially Mycobacteria
  9. Silicosis
    • Chronic inhalation of very fine silicates (quartz)
    • -sandblasters, miners, demolition, sanders

    • Pathophysiology:
    • -engulfed by alveolar macrophages
    • -activation, destruction, re-engulfment cycle

    Presentation: progressive parenchymal destruction

    • Simple silicosis: small nodules on imaging

    • Complicated silicosis: coalescence of nodules, extensive fibrosis, cavities, ...
    • -demonstrates volume loss: R mainstem bronchi is higher than it should be
  10. Coal-worker's pneumoconiosis
    • Coal dust exposure
    • Fibrous and emphysema seen in respiratory bronchioles
    • Classifications: simple vs complicated
    • Coal macules seen on pathology

  11. Asbestosis
    Derivative of silica: straight, sharp, crystalline fibers

    -Chronic exposure: insulation, shipworkers, pipefitters, break pads, Turkey! (NAVY)

    • Deposition of fibers into respiratory bronchioles and alveoli
    • -engulfment by macrophages...
    • -Alveolitis, peribronchial fibrosis, subpleural cysts
    • -Ferruginous bodies: Asbestos fibers coated in iron/protein complex by alveolar macrophages:

    • Pleural disease is common
    • -Benign asbestos pleural effusion (BAPE)
    • -Calcified pleural plaques (calcified lesions mostly benign) ... easy to see on CT

    • Associated with neoplasia:
    • -Adenocarcinoma (especially increased risk when combined with smoking)
    • -Mesothelioma (less common)
  12. Asbestosis ≠ exposure
    • Asbestosis
    • -Fibrotic, destructive process, which can lead to progressive symptoms, disability or death

    • Asbestos exposure along:
    • -may find calcified nodes, effusions, or pleural plaques
    • -fibrotic parenchymal changes are ABSENT
  13. Berylliosis
    • Chronic exposure to beryllium dust
    • -Electronic industry, military jet pilots or mechaniccs, aerospace workers, nuclear weapons

    Clinically may mimic sarcoidosis

    • Dx: Beryllium Lymphocyte Proliferation Test (BeLPT)
    • -Measures response of pt's lymphocytes to beryllium exposure
    • -Pts with berylliosis will show hypersensitive (T cells)
    • -68% sensitive; 97% specific
  14. Hypersensitivity pneumonitis
    • Collection of parenchymal diseases that are characterized by extrinsic allergic alveolitis
    • -Robust immunologic reaction to inhaled organic matter

    • *typically improves with avoidance
    • -pts often asked to change habits to see test exposures

    -Type III or Type IV hypersensitivity reaction

    • Acute:
    • -Sx within hrs
    • -fever, chills, dyspnea, cough
    • -May mimic pneumonia

    • Subacute:
    • -similar to acute, slower onset and less severe

    • Chronic: Most common
    • -Progressive to fibrosis, permanent disease
    • -Historical link may be difficult to find

    • Dx: 
    • -History
    • Pathology: Noncaseating granulomas
    • -cholesterol clefts
    • -Foamy macrophages

    • Radiography:
    • -infiltrates seen along the bronchovascular bundles
    • -fibrosis and honeycombing when advanced or chronic
  15. Hypersensitivity pneumonitis
    • Bird fancier's lung
    • Hot tub lung
    • Farmer's lung
    • Crack lung
    • Maltworker's lung
    • Popcorn worker's lung
    • Penguin humidifier lung
    • Cheese-washer's lung
    • Japanese summer house hypersensitivity pneumonitis
    • Wine-grower's lung
    • ...