A 42-year-old woman with a history of rheumatoid arthritis presents with insidious onset of dyspnea and dry cough over 4 months. Chest X-ray shows bilateral lower lobe interstitial infiltrates. Spirometry reveals: FEV₁ = 68% predicted, FVC = 62% predicted, FEV₁/FVC ratio = 0.88, TLC = 65% predicted, DLCO = 55% predicted. Which of the following best describes the pattern of lung dysfunction?

Explanation

## Restrictive Lung Disease with Impaired Diffusion ### Spirometry Pattern Recognition **Key Point:** The FEV₁/FVC ratio of 0.88 (> 0.70) is **normal or elevated**, which immediately excludes obstructive disease. Both FEV₁ and FVC are proportionally reduced, and TLC is markedly low (65% predicted). **High-Yield:** Restrictive pattern criteria: - FEV₁/FVC ratio **≥ 0.70** (normal or elevated) - FEV₁ reduced (68% predicted) - FVC reduced (62% predicted) - **TLC < 80% predicted** (diagnostic hallmark) - RV reduced ### Pathophysiology: Interstitial Lung Disease This patient's clinical presentation (rheumatoid arthritis, bilateral interstitial infiltrates, dyspnea, dry cough) is consistent with **rheumatoid arthritis-associated interstitial lung disease (RA-ILD)**. The restrictive pattern reflects: 1. **Reduced lung compliance** due to pulmonary fibrosis 2. **Reduced TLC** (65%) — lungs cannot expand normally 3. **Proportional reduction in FEV₁ and FVC** — both limited by stiffness, not airway obstruction ### Diffusing Capacity Impairment **Clinical Pearl:** DLCO = 55% predicted is significantly reduced. In restrictive disease, DLCO reduction indicates: - Destruction of alveolar-capillary interface (fibrosis) - Reduced alveolar surface area - Thickened alveolar membrane This is characteristic of **pulmonary fibrosis** (idiopathic or secondary to RA). ### Differential: Why Not Obstructive? Obstructive disease would show: - FEV₁/FVC ratio **< 0.70** (this patient: 0.88 ✓ normal) - Elevated TLC and RV (this patient: TLC 65% ✗ low) **Mnemonic: RESTRICTIVE DISEASE** - **R**educed FVC, FEV₁, TLC, RV - **E**levated FEV₁/FVC ratio (≥ 0.70) - **S**tiff lungs (low compliance) - **T**hick alveolar walls (low DLCO) - **R**educed gas exchange ```mermaid flowchart TD A["Dyspnea + Interstitial Infiltrates"]:::outcome --> B{"FEV₁/FVC ratio?"}:::decision B -->|"< 0.70"| C["Obstructive Pattern"]:::outcome B -->|"≥ 0.70"| D{"TLC reduced?"}:::decision D -->|"Yes (< 80%)"|E["Restrictive Pattern"]:::outcome D -->|"No (≥ 80%)"|F["Normal spirometry"]:::outcome E --> G["Check DLCO"]:::action G -->|"Low (< 80%)"|H["Interstitial/Fibrotic Disease"]:::outcome G -->|"Normal"|I["Chest wall/Neuromuscular"]:::outcome ``` [cite:Harrison 21e Ch 246]