A 54-year-old woman with primary Sjögren syndrome (anti-RO/SSA and anti-LA/SSB positive) presents with progressive dry cough and exertional dyspnea over 12 months. HRCT chest shows diffuse bilateral centrilobular nodules, thin-walled cysts, and ground-glass opacities. Bronchoalveolar lavage reveals lymphocytic alveolitis with >30% lymphocytes. The pulmonary function pattern marked **B** in the diagram is demonstrated. Which of the following best explains why the DLCO is disproportionately reduced compared to the reduction in FVC and FEV1 in this patient?
A. Small airway obstruction from peribronchiolar lymphoid hyperplasia causing air trapping
B. Emphysematous destruction of alveolar walls leading to loss of surface area
C. Bronchial wall thickening and mucus plugging from follicular bronchiolitis
D. Alveolar-capillary membrane thickening and inflammation from lymphoplasmacytic infiltrate disrupting gas exchange
Explanation
Why "Alveolar-capillary membrane thickening and inflammation from lymphoplasmacytic infiltrate disrupting gas exchange" is right
The restrictive pattern marked B — with proportional reduction in FVC and FEV1, preserved/elevated FEV1/FVC, decreased TLC, and markedly reduced DLCO — is the hallmark of parenchymal interstitial lung disease. In Sjögren-associated LIP, the pathology is diffuse interstitial expansion by polyclonal lymphoplasmacytic infiltrate with germinal centers along bronchovascular bundles and interlobular septa. This infiltrate thickens the alveolar-capillary membrane and impairs oxygen diffusion across the blood-gas interface. The disproportionate reduction in DLCO (48% predicted) relative to the modest reduction in lung volumes reflects a vascular or alveolar-capillary process rather than simple volume loss. This is the defining physiologic signature of LIP and distinguishes it from obstructive patterns (pattern A) or mixed patterns (pattern C). Harrison's 21e and ATS guidelines emphasize that reduced DLCO out of proportion to spirometric reduction indicates parenchymal/interstitial disease.
Why each distractor is wrong
Small airway obstruction from peribronchiolar lymphoid hyperplasia causing air trapping: This describes follicular bronchiolitis, a different Sjögren pulmonary manifestation that produces an obstructive pattern (pattern A: FEV1/FVC <70%, no bronchodilator response), not the restrictive pattern marked B. Air trapping would elevate TLC and preserve or increase DLCO relative to FVC reduction.
Emphysematous destruction of alveolar walls leading to loss of surface area: Emphysema is an obstructive disease (pattern A) with elevated TLC from air trapping. It does not produce the restrictive pattern with decreased TLC shown in B. Additionally, emphysema is not a recognized feature of Sjögren-associated lung disease.
Bronchial wall thickening and mucus plugging from follicular bronchiolitis: Again, this is the pathology of follicular bronchiolitis, which causes small airway disease and an obstructive pattern, not the restrictive pattern B with markedly reduced DLCO characteristic of LIP.
High-YieldNEET PG
In interstitial lung disease, disproportionate DLCO reduction (>10–15% more severe than FVC reduction) signals alveolar-capillary membrane pathology; in Sjögren LIP, this reflects lymphoplasmacytic infiltration and inflammation.
