intersit ld

### Interstitial Lung Disease (ILD) Lecture Notes

#### Learning Outcomes

1. Describe the pathogenesis of interstitial lung diseases.

2. List the causes of interstitial lung diseases.

3. Describe the pathological changes in pulmonary fibrosis.

4. List the causes of occupational lung diseases.

5. Describe the pathology of coal dust, silica, and asbestos-induced lung changes.

6. Describe the pathological features, clinical presentation, and investigations of extrinsic allergic alveolitis.

7. Describe the pathological features, clinical presentation, and investigations of sarcoidosis.

8. Describe the pathological features, clinical presentation, and investigations of Acute Respiratory Distress Syndrome (ARDS).

#### Interstitial Lung Disease (ILD) / Pulmonary Fibrosis

- Definition: A group of diseases causing fibrosis of the pulmonary parenchyma/interstitium, resulting in restrictive defects on pulmonary function.

- Categories:

- Occupational/Environmental (inorganic and organic)

- Idiopathic (e.g., IPF, sarcoidosis, Langerhans cell histiocytosis)

- Drug/Treatment-induced (e.g., amiodarone, bleomycin, radiotherapy)

- Connective Tissue Disorder-associated (e.g., SLE, rheumatoid arthritis, scleroderma, dermatomyositis)

- Post-infectious (e.g., TB)

#### Interstitial Space

- Definition: Loose connective tissue throughout the lung (alveolar walls and septae).

- Subdivisions:

- Bronchovascular: surrounding the bronchi, arteries, and veins from the lung root to respiratory bronchiole.

- Parenchymal: between alveolar and capillary basement membranes.

- Subpleural: beneath the pleura, including interlobular septae.

#### Diagnosis

- Combination of radiographic features and clinical signs/symptoms.

- Radiographic Hallmark: Fibrosis or scarring of the interstitium, which is normally invisible unless involved in disease.

- Clinical Hallmark: Hypoxaemia due to impaired gas diffusion from fibrotic alveolar walls.

#### Classification of ILD

- Based on aetiology, radiology, and histology.

- Radiology: Classified by zones of fibrosis (upper, mid, lower, widespread).

#### Aetiology

- Occupational/Environmental:

- Inorganic (e.g., asbestosis, silicosis, coal)

- Organic (e.g., hypersensitivity pneumonitis from moldy hay, bird faeces)

- Idiopathic: IPF, sarcoidosis, Langerhans cell histiocytosis.

- Drug/Treatment: Amiodarone, bleomycin, radiotherapy.

- Connective Tissue Disorder-Associated: SLE, rheumatoid arthritis, scleroderma, dermatomyositis.

- Post-Infectious: TB.

#### Occupational/Environmental Lung Diseases

- Pneumoconiosis: Lung disease from inhalation of dusts/particles, often related to occupation.

- Inorganic: Asbestosis, silicosis, coal, beryllium.

- Organic: Extrinsic allergic alveolitis/hypersensitivity pneumonitis.

#### Pathogenesis of Pneumoconiosis

- Inhaled particles (1-5 µm most dangerous) reach alveoli, causing lung destruction and fibrosis.

- Factors Influencing Pathogenicity: Size, shape, chemical composition, concentration, solubility, particle reactivity, duration of exposure, co-existing lung diseases.

#### Specific Pneumoconioses

1. Coal Workers’ Pneumoconiosis (CWP):

- Simple CWP: Focal dust accumulation, coal macules, and nodules, usually not disabling.

- Complicated CWP (PMF): Coalescence of coal nodules into black scars, potential pulmonary dysfunction, pulmonary hypertension, and cor pulmonale.

2. Silicosis:

- Caused by inhalation of crystalline silica.

- Acute Silicosis: Rapid onset, severe symptoms, interstitial inflammation.

- Chronic Silicosis: Prolonged exposure, fibrotic nodules.

- Complicated Silicosis (PMF): Coalescence of nodules, progressive respiratory failure, pulmonary hypertension, and cor pulmonale.

3. Asbestosis:

- Due to inhalation of asbestos fibers, leading to interstitial fibrosis (lower zone predominant).

- Asbestos-Related Disorders: Pleural plaques, effusions, mesothelioma, bronchogenic carcinoma.

#### Idiopathic Pulmonary Fibrosis (IPF)

- Definition: Chronic fibrosing interstitial pneumonia of unknown cause.

- Pathogenesis: Persistent alveolar wall injury, inflammatory cell accumulation, fibroblast proliferation, interstitial fibrosis.

- Clinical Features: Gradual onset of dry cough, progressive dyspnoea, clubbing, "velcro crackles," cyanosis, cor pulmonale, peripheral oedema.

#### Sarcoidosis

- Definition: Multisystem granulomatous disease, often involving lungs.

- Aetiology: Unknown; likely immune regulation disorder.

- Clinical Features: Often asymptomatic, but can present with respiratory symptoms, lymphadenopathy, skin lesions, eye involvement, and systemic symptoms.

- Diagnosis: CXR, CT thorax, PFTs, blood tests, lymph node biopsy (non-caseating granulomas).

#### Hypersensitivity Pneumonitis

- Definition: Immune-mediated lung disease from inhalation of organic antigens.

- Pathogenesis: Type III and IV hypersensitivity reactions, leading to pulmonary fibrosis.

- Clinical Features: Acute episodes with fever, malaise, cough, dyspnoea; chronic disease with pulmonary fibrosis.

- Management: Avoidance of allergen, use of air-driven masks, steroids.

This overview condenses the lecture into key points and concepts, focusing on the most crucial information for understanding interstitial lung diseases.