A 68-year-old male smoker with a 2-year history of progressive exertional dyspnoea and dry cough presents with fine bibasilar inspiratory crackles on examination. HRCT shows subpleural, basal-predominant reticulation with traction bronchiectasis and honeycombing consistent with usual interstitial pneumonia (UIP) pattern. Pulmonary function testing reveals the pattern marked **A** in the diagram. Which of the following best describes the expected physiological findings in this patient?

Question

Accepted Answer

B. Reduced FVC and TLC with preserved FEV1/FVC ratio >0.80, and DLCO disproportionately reduced out of proportion to lung volumes. ## Why option 1 is correct

The pattern marked **A** in the diagram represents the restrictive physiology characteristic of idiopathic pulmonary fibrosis (IPF). According to the ATS/ERS/JRS/ALAT 2022 IPF Guideline and INPULSIS trials, IPF presents with a restrictive defect showing reduced FVC and TLC with a preserved or elevated FEV1/FVC ratio (typically >0.80). Critically, DLCO is disproportionately reduced out of proportion to lung volumes, reflecting the alveolar membrane destruction and epithelial-capillary injury that characterizes UIP histology. This disproportionate DLCO reduction is a hallmark physiological finding in IPF and helps distinguish it from other restrictive diseases.

## Why each distractor is wrong

- **Option 2**: This describes an obstructive pattern (pattern **B** in the diagram) with reduced FEV1/FVC ratio <0.70 and reversibility, typical of asthma or COPD, not the restrictive physiology of IPF.
- **Option 3**: This describes a mixed obstructive-restrictive pattern (pattern **C** in the diagram), which does not fit the pure restrictive defect seen in uncomplicated IPF.
- **Option 4**: This describes normal lung function (pattern **D** in the diagram) or very early disease, which would not be consistent with the clinical presentation of progressive dyspnoea, bibasilar crackles, and definite UIP on HRCT.

**High-Yield:** In IPF, DLCO is disproportionately reduced relative to FVC—this mismatch is a key diagnostic clue and prognostic marker; a ≥15% decline in DLCO over 6–12 months signals disease progression and triggers therapeutic escalation.

[cite: ATS/ERS/JRS/ALAT IPF Guideline 2022; INPULSIS NEJM 2014]

Answer

A. Reduced FEV1/FVC ratio <0.70 with normal TLC, indicating airway obstruction with reversibility on bronchodilator challenge

Answer

C. Mixed reduction in FEV1 and FVC with FEV1/FVC ratio 0.65–0.75, reflecting combined airway and parenchymal disease

Answer

D. Normal FVC, TLC, and DLCO with only mild reduction in FEV1, indicating early-stage disease without significant functional impairment

Explanation

Why option 1 is correct

Why each distractor is wrong

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