A 42-year-old woman with a history of systemic sclerosis presents with progressive dyspnea over 6 months. She reports dyspnea on exertion climbing one flight of stairs. Chest examination is unremarkable. Spirometry reveals FEV₁ = 68% predicted, FVC = 62% predicted, FEV₁/FVC ratio = 0.88. Total lung capacity is 58% predicted, and residual volume is 35% predicted. Diffusion capacity (DLCO) is 45% predicted. Which spirometric pattern is demonstrated, and what is the most likely underlying pathophysiology?

Explanation

## Restrictive Pattern in Pulmonary Fibrosis **Key Point:** The FEV₁/FVC ratio of 0.88 (> 0.70) with reduced FVC (62% predicted) and reduced TLC (58% predicted) defines a **restrictive pattern**. The markedly reduced DLCO (45% predicted) confirms interstitial lung disease (ILD), consistent with systemic sclerosis-associated pulmonary fibrosis. ### Spirometric Pattern Analysis | Parameter | Value | Interpretation | |-----------|-------|----------------| | FEV₁ | 68% predicted | Mildly-moderately reduced | | FVC | 62% predicted | **Reduced (primary defect)** | | FEV₁/FVC | 0.88 | **Restrictive** (> 0.70) | | TLC | 58% predicted | **Reduced (confirms restriction)** | | RV | 35% predicted | Reduced | | DLCO | 45% predicted | **Severely reduced** | ### Pathophysiology of Restrictive Pattern **High-Yield:** In pulmonary fibrosis: 1. **Reduced elastic compliance** → lungs cannot expand normally → ↓ TLC, ↓ FVC 2. **Proportional reduction in FEV₁ and FVC** → FEV₁/FVC ratio remains normal or elevated (> 0.70) 3. **Alveolar-capillary thickening** → ↓ DLCO (out of proportion to spirometric reduction) **Clinical Pearl:** The disproportionate reduction in DLCO (45%) relative to FVC (62%) is a hallmark of ILD. This "DLCO out of proportion" pattern is highly suggestive of fibrosis rather than simple restriction from chest wall disease. **Mnemonic:** **RESTRICTIVE = R**educed **FVC** (primary), **R**aised **FEV₁/FVC** (> 0.70), **R**educed **TLC**. Remember: "Restrictive lungs are small lungs" — all volumes shrink proportionally. ### Systemic Sclerosis and Pulmonary Involvement - Pulmonary fibrosis occurs in 40–75% of systemic sclerosis patients - Pattern: usual interstitial pneumonia (UIP) or nonspecific interstitial pneumonia (NSIP) - DLCO reduction is often the **earliest functional abnormality**, preceding spirometric changes - Progressive dyspnea on exertion is the typical presenting symptom