Restrictive Lung Disease USMLE Step 1 Practice Question
A 55-year-old man with a 3-year history of sarcoidosis presents to clinic with progressive dyspnea on exertion over the past 6 months. He denies fever, night sweats, or weight loss. Physical examination reveals clear lung fields bilaterally. Vital signs are stable with SpO2 92% on room air at rest. Laboratory studies show serum calcium 11.8 mg/dL (normal 8.5-10.5), elevated angiotensin-converting enzyme (ACE) at 72 U/L, and normal liver and renal function. Chest radiograph demonstrates bilateral hilar lymphadenopathy with clear lung parenchyma and no evidence of pulmonary fibrosis. Pulmonary function tests show FVC 75% predicted, FEV1 78% predicted, FEV1/FVC ratio 93% (normal), and DLCO 58% predicted. Which of the following best explains the disproportionately reduced DLCO relative to the preservation of spirometric lung volumes?
Answer choices
- AGranulomatous inflammation and infiltration of the alveolar-capillary membraneCorrect answer
- BEndobronchial granulomas causing small airway obstruction with air trapping
- CCardiac involvement with reduced pulmonary capillary blood flow
- DMediastinal lymphadenopathy compressing the pulmonary veins
- ERespiratory muscle involvement limiting maximal inspiration effort
- FHypercalcemia-induced nephrogenic diabetes insipidus reducing plasma volume
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