Restrictive Lung Disease USMLE Step 1 Practice Question
A 41-year-old man with a 6-year history of systemic sclerosis presents to clinic with progressive dyspnea on exertion over the past 8 months. He denies orthopnea or paroxysmal nocturnal dyspnea. Physical examination reveals normal lung sounds bilaterally, no clubbing, and normal jugular venous pressure. Vital signs: BP 138/86 mmHg, HR 102 bpm, RR 22/min, SpO2 88% on room air. Chest X-ray shows fine reticular opacities predominantly at the lung bases. Pulmonary function testing demonstrates: FVC 65% predicted, FEV1 62% predicted, FEV1/FVC ratio 78%, and DLCO 45% predicted. Transthoracic echocardiography shows normal left ventricular ejection fraction and estimated right ventricular systolic pressure of 55 mmHg. Which of the following best explains the disproportionately reduced DLCO relative to the reduction in FVC?
Answer choices
- AInterstitial pulmonary fibrosis with inflammation limiting gas diffusion surface area
- BSystemic anemia reducing effective hemoglobin available for oxygen binding
- CPulmonary vasculitis causing capillary dropout and reduced vascular bedCorrect answer
- DLeft ventricular diastolic dysfunction impairing alveolar fluid clearance
- EPleural thickening from systemic sclerosis reducing pleural compliance
- FBronchiolar obstruction from smooth muscle proliferation in small airways
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