A 42-year-old woman from Mumbai with a history of systemic sclerosis presents with progressive dyspnea and reduced exercise tolerance over 2 years. Physical examination reveals reduced chest expansion and fine end-inspiratory crackles at both lung bases. Spirometry shows: FEV₁ = 68% predicted, FVC = 62% predicted, FEV₁/FVC ratio = 0.82. DLCO = 55% predicted. What is the most likely spirometric pattern and its pathophysiologic basis?

Question

Accepted Answer

C. Restrictive pattern due to pulmonary fibrosis with reduced DLCO from alveolar-capillary thickening. ## Restrictive Pattern in Pulmonary Fibrosis

### Pattern Recognition

**Key Point:** FEV₁/FVC ratio of 0.82 (>0.70) with proportional reduction in both FEV₁ (68%) and FVC (62%) is diagnostic of a **restrictive pattern**. The key is that both volumes are reduced proportionally, preserving the ratio.

### Diagnostic Criteria Table

| Feature | This Patient | Restrictive | Obstructive | Normal |
|---------|-------------|------------|------------|--------|
| FEV₁/FVC | 0.82 | >0.70 | <0.70 | >0.80 |
| FEV₁ | 68% | ↓ | ↓ | Normal |
| FVC | 62% | ↓ | Normal/↑ | Normal |
| TLC | Expected ↓ | ↓ | Normal/↑ | Normal |
| DLCO | 55% | ↓ | Normal (unless emphysema) | Normal |

### Pathophysiology of DLCO Reduction in Fibrosis

**High-Yield:** In pulmonary fibrosis, DLCO is reduced because:
1. **Alveolar-capillary membrane thickening** (fibrotic tissue) increases diffusion distance
2. **Capillary bed destruction** reduces available surface area for gas exchange
3. **V/Q mismatch** from irregular ventilation in scarred lung

This is in contrast to emphysema (also obstructive + low DLCO), where the mechanism is capillary loss without membrane thickening.

### Clinical Correlation

**Clinical Pearl:** Systemic sclerosis (scleroderma) is a well-known cause of pulmonary fibrosis. The combination of:
- Fine end-inspiratory crackles (Velcro crackles typical of fibrosis)
- Progressive dyspnea
- Reduced chest expansion (skin thickening + lung restriction)
- Restrictive spirometry with low DLCO

...is pathognomonic for interstitial lung disease (ILD).

**Mnemonic for Restrictive Causes:** **CREST** (scleroderma) + **ABCDEFG** (other ILDs):
- **A**sbestosis, **A**ntigen exposure (hypersensitivity pneumonitis)
- **B**erylliosis, **B**eryllium
- **C**oal dust, **C**ryptogenic organizing pneumonia
- **D**rug-induced (bleomycin, nitrofurantoin), **D**ust (silicosis)
- **E**xtrinsic allergic alveolitis
- **F**ibrosis (idiopathic pulmonary fibrosis, sarcoidosis)
- **G**ranulomatosis (sarcoidosis, TB)

[cite:Harrison 21e Ch 248]

Answer

A. Mixed pattern indicating both airway obstruction and parenchymal disease

Answer

B. Normal spirometry with isolated DLCO reduction indicating early interstitial disease

Answer

D. Obstructive pattern with air trapping causing apparent FVC reduction

Explanation

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