Restrictive Lung Diseases

Restrictive Lung Disease

Volume Limitation & Compliance

FreeMedSite USMLE STEP 1 REVIEW

Interactive Diagnostics:

Pathophysiology

Characterized by Decreased Compliance (stiff lungs) and Increased Elastic Recoil. This leads to a Rightward Shift of the Pressure-Volume loop.

Spirometry (PFTs)

Defining Metric

TLC ↓ (Required)

Total Lung Capacity must be low

Flow/Volume Ratio

FEV₁/FVC ≥ 80%

Normal or Increased

FVC: ↓↓ FEV₁: ↓ Residual Vol (RV): ↓

Physical Exam

Auscultation

Inspiratory Crackles

"Velcro-like"

Inspections

Digital Clubbing

Late finding in fibrosis

Diagnostic Logic

Extrapulmonary (Obesity, Scoliosis, Polio)

DLCO

Normal

A-a Gradient

Normal

Pulmonary Parenchymal (IPF, Sarcoid)

DLCO

Decreased (↓)

A-a Gradient

Increased (↑)

Etiology Flashcards

Neuromuscular Weakness

Identify 4 causes: Polio, MG, Guillain-Barré, ALS

Drug-Induced Fibrosis

Recall the 4 main drugs: Bleomycin, Busulfan, Amiodarone, Methotrexate

Sarcoidosis Markers

Hilar nodes plus: ↑ ACE, ↑ Calcium, non-caseating granulomas

Radiation Injury

Cytokines involved: TNF-α, IL-1, IL-6

🔍

Core Concept

• • ↓ Lung volumes
• • ↓ FVC (Forced Vital Capacity)
• • ↓ TLC (Total Lung Capacity)
• • FEV₁/FVC ratio = Normal or ↑
• • Short, shallow breathing / Progressive dyspnea

📊 Types of Restrictive Lung Disease

1. Extrapulmonary

Problem is outside the lungs → lungs are normal but cannot expand properly

DLCO

Normal

A–a gradient

Normal

Muscle Weakness

Post-Polio, Myasthenia Gravis, GBS, ALS

Chest Wall

Scoliosis, Severe Obesity

2. Pulmonary (Parenchymal)

Problem is within lung tissue itself

DLCO

↓ Decreased

A–a gradient

↑ Increased

• Pneumoconiosis

• Sarcoidosis (Bilateral Hilar Nodes)

• Idiopathic Pulmonary Fibrosis

• Granulomatosis with Polyangiitis

• Langerhans Cell Histiocytosis

• Hypersensitivity Pneumonitis

• Drug-Induced Fibrosis

• ARDS

☢️ Radiation-Induced Injury

Mechanism:

Release of inflammatory cytokines: TNF-α, IL-1, IL-6

Timeline:

• • Acute Pneumonitis: 3–12 weeks
• • Radiation Fibrosis: 6–12 months later

🔥 High-Yield Summary

• Restrictive = ↓ lung expansion → ↓ TLC & FVC

• FEV₁/FVC = Normal or ↑

• DLCO helps differentiate: Normal (Extra) vs ↓ (Parenchymal)

• A–a gradient: Normal (Extra) vs ↑ (Lung pathology)