Restrictive Pulmonary Diseases

RLDs Overview - Lungs Under Pressure

RLDs: Group of disorders causing ↓ lung expansion & ↓ Total Lung Capacity (TLC).

• Pathophysiology: ↑ Lung stiffness (↓ compliance) or chest wall/neuromuscular dysfunction.
• Key PFTs:
  • Hallmark: ↓ TLC (<80% predicted)
  • ↓ FVC, ↓ FEV1
  • FEV1/FVC ratio: Normal or ↑ (typically >0.7 as both ↓ proportionally or FVC ↓ more)
  • ↓ DLCO (common in parenchymal RLDs)
• Types:
  • Intrinsic (Parenchymal): IPF, Sarcoidosis
  • Extrinsic: Kyphoscoliosis, Myasthenia Gravis

⭐ Hallmark of RLDs is a decreased Total Lung Capacity (TLC) with a normal or increased FEV1/FVC ratio.

IIPs Deep Dive - Mysterious Fibrosis

Idiopathic Interstitial Pneumonias (IIPs): Group of diffuse parenchymal lung diseases of unknown cause, characterized by varying degrees of inflammation and fibrosis. Focus on IPF.

• Idiopathic Pulmonary Fibrosis (IPF): Most common and severe IIP.
  • Etiology: Unknown; associations: smoking, genetics (e.g., MUC5B, TERT, TERC).
  • Pathology: Usual Interstitial Pneumonia (UIP) pattern is the hallmark.
    • Key features: Temporal heterogeneity (old & new fibrosis), spatial heterogeneity (patchy), fibroblastic foci (active fibrosis), architectural distortion.
    • Gross/CT: Honeycomb lung (esp. subpleural, basal).
  • Clinical: Insidious onset dyspnea, dry cough, digital clubbing, bibasilar inspiratory crackles ("velcro rales").
  • Diagnosis: HRCT (typical UIP: subpleural, basal predominant reticulation, honeycombing, traction bronchiectasis). Biopsy if HRCT atypical.
  • Prognosis: Poor, median survival ~3-5 years post-diagnosis.

  ⭐ Fibroblastic foci are crucial microscopic findings in UIP, representing sites of ongoing, active collagen deposition by myofibroblasts.

• Other notable IIPs:
  • Non-Specific Interstitial Pneumonia (NSIP): Better prognosis than IPF; cellular or fibrotic patterns.
  • Cryptogenic Organizing Pneumonia (COP): Good response to steroids.

Occupational & Environmental RLDs - Inhaled Insults

• Pneumoconioses: Inorganic dust inhalation → macrophage activation → fibrosis.

  • Coal Worker's Pneumoconiosis (CWP): Coal dust. Simple (macules/nodules <1cm, upper lobes); Complicated (Progressive Massive Fibrosis, PMF >2cm). Caplan Syndrome (CWP + RA nodules).

  • Silicosis: Silica dust (mining, sandblasting). ↑ TB risk (impaired macrophage function). Eggshell calcification of hilar lymph nodes. Apical fibronodules.

  • Asbestosis: Asbestos fibers. Ferruginous bodies. Pleural plaques (most common manifestation, parietal). Basilar predominant fibrosis. ↑ Risk: Bronchogenic carcinoma (most common cancer), mesothelioma.

  • Berylliosis: Beryllium exposure. Non-caseating granulomas; mimics sarcoidosis.

• Hypersensitivity Pneumonitis (HP): Immune-mediated (Type III/IV hypersensitivity) response to inhaled organic antigens.
  • Examples: Farmer's lung (Saccharopolyspora rectivirgula), Bird fancier's lung (avian proteins).
  • Acute: Fever, cough, dyspnea 4-8 hrs post-exposure; reversible. Chronic: Insidious onset, progressive dyspnea, irreversible fibrosis; non-caseating granulomas.

⭐ In asbestosis, bronchogenic carcinoma is a more common malignancy than mesothelioma, especially with co-existing smoking (synergistic effect).

Systemic & Other RLDs - Wider Connections

• Connective Tissue Diseases (CTDs) causing RLD:
  • Systemic Sclerosis (Scleroderma): Most common CTD to cause ILD (NSIP pattern common).
  • Rheumatoid Arthritis (RA): Usual Interstitial Pneumonia (UIP) pattern common; Caplan syndrome (RA + pneumoconiosis).
  • Systemic Lupus Erythematosus (SLE): Pleuritis, pleural effusions, acute lupus pneumonitis, diffuse alveolar hemorrhage, shrinking lung syndrome.
  • Polymyositis/Dermatomyositis: NSIP, organizing pneumonia.
  • Sjögren's Syndrome: Lymphocytic interstitial pneumonia (LIP).
• Drug-Induced RLDs:
  • Amiodarone: Pneumonitis, fibrosis.
  • Bleomycin: Dose-dependent pneumonitis, fibrosis.
  • Methotrexate: Hypersensitivity pneumonitis.
  • Nitrofurantoin: Acute pneumonitis, chronic fibrosis.
  • 📌 Mnemonic: "Bad Air Makes No Lungs Happy" (Bleomycin, Amiodarone, Methotrexate, Nitrofurantoin, Lomustine (CCNU), Heroin)
• Radiation-Induced Lung Disease:
  • Radiation Pneumonitis: Acute (1-6 months post-radiation); lymphocytic alveolitis.
  • Radiation Fibrosis: Chronic (>6-12 months post-radiation); dense fibrosis.

⭐ Amiodarone lung toxicity classically shows foamy macrophages on BAL or biopsy due to phospholipidosis, and high-attenuation areas on CT scan due to iodine content.

• Other Causes:
  • Neurofibromatosis
  • Tuberous Sclerosis (LAM - Lymphangioleiomyomatosis)
  • Graft-versus-Host Disease (GVHD) post-transplant (Bronchiolitis Obliterans).

High‑Yield Points - ⚡ Biggest Takeaways

• Restrictive diseases: ↓ lung volumes (↓TLC, ↓FVC), normal/↑ FEV1/FVC ratio.
• IPF: Usual Interstitial Pneumonia (UIP) pattern, honeycomb lung on HRCT.
• Sarcoidosis: Non-caseating granulomas, bilateral hilar lymphadenopathy, ↑ACE.
• Pneumoconioses: Caused by inorganic dust inhalation (e.g., silica, asbestos), leading to fibrosis.
• Asbestosis: Associated with pleural plaques, ↑ risk of mesothelioma and bronchogenic carcinoma.
• Hypersensitivity Pneumonitis: Immune reaction to inhaled organic antigens (e.g., farmer's lung).
• ARDS: Characterized by Diffuse Alveolar Damage (DAD) and hyaline membrane formation.