A 42-year-old woman with a history of rheumatoid arthritis presents with insidious dyspnea and a dry cough for 3 months. Chest X-ray shows bilateral lower lobe interstitial infiltrates. Spirometry reveals FEV₁ = 68% predicted, FVC = 62% predicted, FEV₁/FVC ratio = 0.88. DLCO is 58% predicted. What is the most likely spirometric pattern?

Explanation

## Restrictive Lung Disease Pattern **Key Point:** FEV₁/FVC ratio >0.80 (here 0.88) with reduced FVC (<80% predicted) defines a **restrictive pattern**. Both FEV₁ and FVC fall proportionally, preserving the ratio. ### Spirometric Pattern Breakdown | Parameter | Value | Interpretation | | --- | --- | --- | | FEV₁ | 68% predicted | Reduced | | FVC | 62% predicted | **Significantly reduced** | | FEV₁/FVC | 0.88 | **Preserved (>0.80)** | | DLCO | 58% predicted | **Markedly reduced** | **High-Yield:** In restriction, the lungs cannot expand fully (reduced TLC). Both FEV₁ and FVC decrease together, so their ratio remains normal or even supranormal. The hallmark is **reduced FVC with normal/high FEV₁/FVC ratio**. ### Clinical Context: Interstitial Lung Disease (ILD) - **Rheumatoid arthritis** — major risk factor for RA-associated ILD (RA-ILD) - **Bilateral lower lobe infiltrates** — typical ILD distribution - **Markedly reduced DLCO (58%)** — indicates alveolar-capillary inflammation/fibrosis; DLCO is the most sensitive early marker of ILD - **Dry cough, insidious dyspnea** — classic ILD presentation **Clinical Pearl:** DLCO reduction out of proportion to spirometric changes is a red flag for early ILD. This patient's DLCO (58%) is much worse than FEV₁ (68%), suggesting active alveolar disease. **Mnemonic: RESTRICTIVE SPIROMETRY** = FVC ↓↓, FEV₁/FVC >0.80, DLCO ↓ [cite:Harrison 21e Ch 309]