Chronic interstitial (restrictive) lung diseases

Overview: Restrictive vs. Obstructive

• Restrictive (interstitial) lung diseases: ↓ lung compliance → ↓ total lung capacity + ↓ FVC; FEV₁ is normal → FEV₁/FVC ratio ~normal (vs. COPD where ratio is ↓)
• Divided into: Acute (ARDS) and Chronic (below)

Chronic restrictive diseases:

• Fibrosing: IPF, non-specific interstitial pneumonia, pneumoconioses
• Granulomatous: Sarcoidosis
• Smoking-related: desquamative interstitial pneumonia, respiratory bronchiolitis

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Pneumoconiosis (Overview)

• Disease of the lung due to inhalation of dust (occupational exposure)
• Most common:
  • Coal dust → coal worker’s pneumoconiosis (CWP)
  • Silica → silicosis
  • Asbestos → asbestosis

Pathogenesis (shared)

• Particles 1–5 µm are the most dangerous (lodge at distal airway bifurcations)
• Particles trapped in alveolar duct bifurcation → endocytosed by macrophages →:
  1. Reactive particles kill the macrophage → lysosomal enzyme release
  2. Particles trigger macrophages to release inflammatory mediators → necrosis → fibrosis → alveolar/capillary destruction → ↑ lung resistance → cor pulmonale
• Coal dust is relatively inert; silica and asbestos are more reactive at lower concentrations
• Tobacco smoke worsens all pneumoconioses

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1. Coal Worker’s Pneumoconiosis (CWP)

Categories

Asymptomatic anthracosis (most harmless)

• Inhaled carbon phagocytosed by alveolar macrophages → transported to lymph nodes → black pigmentation
• Seen in smokers and urban residents

Simple CWP (3 findings):

• Coal macule: dust-laden macrophages (<7 mm)
• Coal nodule: dust-laden macrophages + collagen fibers (≥2 cm)
• Centrilobular emphysema may coexist

Complicated CWP = Progressive Massive Fibrosis (PMF):

• Background of simple CWP + merging of coal nodules
• Macroscopy: intensely blackened scars >2 cm (usually multiple)
• Only PMF produces pulmonary dysfunction, pulmonary hypertension, and cor pulmonale

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2. Silicosis

• Inhalation of crystalline silica (highly toxic, insoluble)
• Pathogenesis: silica → macrophage phagocytosis → macrophage death (SiOH) → lysosomal enzyme release → necrosis → fibrosis → fibrotic nodules → alveolar/capillary destruction → cor pulmonale
• Morphology: fibrotic nodule, progressive massive fibrosis, alveolar proteinosis (abnormal surfactant accumulation → impairs gas exchange)
• Clinical: dyspnea develops late; increased susceptibility to tuberculosis (inhibits macrophage function)

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3. Asbestosis

• Inhalation of asbestos (crystalline hydrated silicates with fibrous geometry)
• Occupational exposure linked to:
  • Parenchymal interstitial fibrosis (asbestosis)
  • Localized fibrous pleural plaques or diffuse pleural fibrosis
  • Pleural effusions
  • Bronchogenic carcinoma
  • Malignant mesothelioma (pleural + peritoneal)
  • Laryngeal carcinoma
• Asbestos = tumor initiator and promoter

Morphology

• Diffuse pulmonary interstitial fibrosis
• Distinguishing feature: asbestosis bodies — golden-brown, fusiform-shaped with translucent center; central asbestos fiber core coated with iron-protein-mucopolysaccharide layer
• Detected with Prussian blue iron stain
• Histology: bronchiolocentric fibrosis to honeycomb lung
• Pleural plaques: dense collagen + calcium; most common manifestation of asbestos exposure

Clinical

• Dyspnea, cough, sputum (like any diffuse interstitial lung disease)
• May remain static or progress to CHF, cor pulmonale, death
• Increased cancer risk

💡 High-yield: Restrictive = ↓ TLC + ↓ FVC; FEV₁/FVC normal. Pneumoconioses: particles 1–5 µm most dangerous. CWP: PMF is only dangerous form. Silicosis: ↑ TB susceptibility. Asbestosis: mesothelioma risk + asbestosis bodies (Prussian blue+) + pleural plaques.