## Why option 1 is right The restrictive pattern marked **A** (reduced FVC with preserved FEV1/FVC ratio) in sarcoidosis results from the pathognomonic non-caseating granulomatous inflammation. The CD4+ Th1-mediated immune response (with BAL CD4/CD8 ratio >3.5) drives accumulation of epithelioid granulomas in the lung parenchyma, causing thickening of the alveolar-capillary membrane and reducing both lung volumes (FVC, TLC) and gas exchange (DLCO 55%). This is the defining histopathologic and functional signature of pulmonary sarcoidosis per ATS/ERS/WASOG 2020 and Harrison's 21st edition. ## Why each distractor is wrong - **Option 2 (Obstructive airway disease)**: Sarcoidosis produces a RESTRICTIVE pattern with preserved FEV1/FVC ratio (0.82), not an obstructive pattern. Obstruction would show FEV1/FVC <0.70 and air trapping on TLC. Mucus plugging is not the mechanism in sarcoidosis. - **Option 3 (IgE-mediated bronchospasm)**: Sarcoidosis is a Th1-mediated granulomatous disease, not an IgE-mediated allergic condition. Bronchospasm would produce obstruction, not restriction. This confuses sarcoidosis with asthma or atopy. - **Option 4 (Emphysematous destruction)**: Emphysema causes obstruction with air trapping (elevated TLC), not restriction. The DLCO may be reduced in emphysema, but the spirometric pattern differs fundamentally. This describes COPD, not sarcoidosis. **High-Yield:** Sarcoidosis = non-caseating granulomas + Th1/CD4+ response + RESTRICTION (low FVC, preserved FEV1/FVC) + reduced DLCO = parenchymal inflammation, not airway obstruction. [cite: ATS/ERS/WASOG Sarcoidosis Statement 2020; Harrison's Principles of Internal Medicine, 21st ed]
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