A 62-year-old woman with rheumatoid arthritis presents with progressive exertional dyspnea and dry cough over 14 months. Examination reveals fine end-inspiratory crackles at lung bases, SpO2 91% at rest, and desaturation to 85% on 6-minute walk. HRCT shows UIP pattern with basal honeycombing. Spirometry shows FEV1 1.65 L (72% predicted), FVC 2.10 L (68% predicted), and FEV1/FVC 0.79. The flow-volume loop demonstrates a narrow, tall morphology with reduced volume and preserved peak expiratory flow. Body plethysmography shows TLC 3.85 L (65% predicted).
The pattern marked **A** in the diagram — normal FEV1/FVC >0.70 with proportional reduction in both FEV1 and FVC, and reduced TLC <80% — confirms which diagnosis?
A. Asthma with incomplete post-bronchodilator reversibility and normal lung volumes
B. Mixed obstructive-restrictive defect with elevated residual volume and reduced FVC
C. Obstructive airway disease with air trapping and preserved FEV1/FVC ratio
D. Restrictive lung disease secondary to rheumatoid arthritis-associated interstitial lung disease (RA-ILD) with UIP pattern
Explanation
Why "Restrictive lung disease secondary to rheumatoid arthritis-associated interstitial lung disease (RA-ILD) with UIP pattern" is right
The pattern marked A — characterized by normal or elevated FEV1/FVC ratio (>0.70), proportional reduction in both FEV1 and FVC, and confirmed TLC <80% on body plethysmography — is the hallmark of restrictive lung disease. This patient's clinical presentation (progressive dyspnea, fine crackles, HRCT showing UIP pattern with honeycombing, and disproportionately reduced DLCO at 55% predicted) is pathognomonic for RA-ILD. The preserved FEV1/FVC ratio distinguishes restriction from obstruction, and the reduced TLC (65% predicted) definitively confirms the restrictive physiology. Per Harrison's Chapter 289 and ATS/ERS 2017 standards, this spirometric and lung volume pattern is diagnostic of restrictive disease, with RA-ILD being the most likely etiology given her RA history, RF/anti-CCP positivity, and imaging findings.
Why each distractor is wrong
Obstructive airway disease with air trapping and preserved FEV1/FVC ratio: Obstruction is defined by FEV1/FVC <0.70; this patient's ratio is 0.79 (normal). Additionally, obstructive disease shows elevated TLC and RV/TLC ratio due to air trapping, not reduced TLC as seen here (TLC 65% predicted).
Asthma with incomplete post-bronchodilator reversibility and normal lung volumes: Asthma typically presents with FEV1/FVC <0.70 and reversibility post-bronchodilator. This patient showed no significant reversibility and has reduced TLC (65% predicted), not normal lung volumes. The HRCT UIP pattern is incompatible with asthma.
Mixed obstructive-restrictive defect with elevated residual volume and reduced FVC: Mixed defects show FEV1/FVC <0.70 with reduced TLC. This patient's FEV1/FVC is normal (0.79), and RV is actually reduced (72% predicted), not elevated—a key feature distinguishing restriction from obstruction.
High-YieldNEET PG
In restrictive lung disease, FEV1/FVC is normal or elevated (>0.70), both FEV1 and FVC are proportionally reduced, TLC is <80% predicted, and RV/TLC ratio is normal or low—opposite of obstruction where FEV1/FVC <0.70 and RV/TLC is elevated.
Harrison's Principles of Internal Medicine, 21st ed., Chapter 289: Interstitial Lung Diseases; ATS/ERS 2017 Pulmonary Function Test Standards
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