L67: Diffuse Interstital Lung Diseases Flashcards
Pulmonary interstitium
Tissue and space around air sacs of lung
- Alveolar septa
- Peribronchiolar tissue
- Perivascular
Diffuse interstitial lung disease
Acute mild:
- interstitial pneumonitis (viral)
Acute severe:
- Diffuse alveolar damage (DAD)
Chronic:
- Idiopathic pulmonary fibrosis
- Pneumoconiosis: Silicosis, Asbestosis
- heterogeneous pattern
- ALL result in diffuse fibrosis —> Restrictive lung function
Diffuse alveolar damage
Caused by:
- lung injuries: gastric aspiration, viral / mycoplasma pneumonitis, toxic fume, drowning
- general injuries: sepsis, shock, pancreatitis
Pathogenesis:
- injury to epithelium / endothelium
—> inflammatory cytokines
—> alveolar wall necrosis
- Capillary leak —> oedema, RBC, serum protein leakage
- Loss of surfactant —> alveolar collapse —> decreased compliance, increased stiffness
- Damage to pneumocyte, interstitial cells, lymphocyte infiltration (Type 2 pneumocyte hyperplasia replacing type 1 pneumocyte) —> cell debris, fibrinous exudate —> hyaline membrane —> impaired diffusion capacity —> VQ mismatch
Result:
- Decreased lung compliance
- Impaired diffusion capacity
- VQ mismatch
Symptoms:
- rapidly deteriorating respiratory failure (Type 1: gas exchange failure)—> hypoxaemia
- Acute Respiratory Distress Syndrome (ARDS)
- 30-40% mortality
- fibrosis in surviving patients
Chronic interstitial lung disease
**Chronic inflammation + **Fibrosis of lung
Caused by:
- result from recurrent / continuous / severe lung damage
- toxic damages: toxic fume, irradiation, prolonged hyperbaric oxygen
- mineral dust: pneumoconiosis
- auto-immune: SLE, systemic sclerosis
- sarcoidosis, allergic condition
- Idiopathic pulmonary fibrosis
- Pneumoconiosis
Idiopathic pulmonary fibrosis and Pathogenesis
- slow progressive changes: not notice until late fibrotic stage
- diffuse, chronic damage, interstitial inflammation (advanced stage: honeycomb lung)
Pathogenesis:
- B, T cell produce immunocomplex + cytokines to activate macrophage
—> activated macrophage recruit neutrophil + fibroblast
—> together damage type 1 pneumocyte
—> type 2 pneumocyte proliferate and recruit more fibroblast
—> 1. Fibroblast proliferation
—> 2. Ingrowth of bronchiolar epithelium
—> 3. Chronic inflammation
Pathology of idiopathic pulmonary fibrosis
- Interstitial fibrosis (stained pink)
- ↓ compliance —> stiff, rigid lung
- reduced capillaries —> ↓ gas exchange —> impaired perfusion
- alveolar fibrosis —> ↓SA + ↓ diffusion capacity —> VQ mismatch - Obliteration and cystic dilation of air space
Gross appearance (restrictive pattern):
- Rigid shrunken lung (sense/fibrosis)
- Thickened alveolar wall (pinhole alveolar space)
- Honeycomb lung (End stage changes)
Symptoms of end-stage diffuse ILD
- Dry cough
- SOB but no wheeze
- chronic hypoxia —> cyanosis
- coarse lines and nodules on CXR
- risk of lung cancer
Diagnosis of ILD
History: no caused found - idiopathic
Clinically:
Restrictive lung function (FEV1/FVC > 80%, disproportionately larger decrease in FVC)
Radiologically:
Interstitial thickening
Pathologically:
Tissue reaction pattern (acute inflammation vs fibrosis)
Pneumoconiosis
**Chronic inflammation + **Fibrosis due to inhalation of inorganic dust
- depends on chemical nature, physical state, particle size, duration and concentration of exposure
- Silicosis
- Asbestosis
Silicosis
Prolonged and massive exposure to Silica (silicon dioxide): quartz-mining, rock-cutting, glass-making, sand-blasting
Silicotic nodules
- Fibroblast proliferation —> interstitial fibrosis
- Chronic inflammation
Advanced stage:
- Honeycomb lung
- Respiratory failure
- Cor pulmonale
Asbestosis
Asbestos: Fibrous magnesium silicate
- Long, thin, curved/straight fibre
- needle-like —> caused bleeding —> iron deposition
Asbestos bodies:
- asbestos fibre covered by film of protein impregnated with haemosiderin
- long, beaded, brownish
- Hallmark of asbestos exposure
- found in bronchial fluids and sputum
—> Fibroblast proliferation —> interstitial fibrosis
—> Chronic inflammation
Asbestos-related conditions
- Malignant Mesothelioma (cancer of mesothelium: pleura)
Effects of chronic hypoxia
—> Pulmonary vasoconstriction
- Early: reversible
- Late: irreversible structural change: increased fibroblast and smooth muscle cell —> thickening of tunica media and intima
—> Polycythaemia: increased blood viscosity
—> Pulmonary hypertension (type 3)
—> Right ventricular hypertrophy / dilatation (systemic venous congestion)
—> Cor pulmonale
Acute vs Chronic ILD
Acute:
- Interstitial pneumonitis
- DAD
Chronic
- heterogeneous pattern
- ALL result in diffuse fibrosis —> Restrictive lung function
