A 45-Year-Old Man Comes to the Office Due to Progressive

A 45-year-old man comes to the office due to progressive dyspnea on exertion and cough for the past several weeks.  He has had no fever, chills, chest pain, or leg swelling.  The patient is a former smoker with 5-pack-year history.  Temperature is 37.2 C (99 F) , blood pressure is 120/70 mm Hg, pulse is 82/min, and respirations are 16/min.  The patient is hypoxemic at rest, with an oxygen saturation of 88% on room air.  Jugular venous pressure is normal.  Lung auscultation shows scattered crackles.  Heart sounds are normal.  Chest x-ray reveals bilateral midalveolar and lower alveolar opacities.  Transbronchial lung biopsy reveals lipoproteinaceous material that is positive on periodic acid-Schiff stain and fills up the terminal bronchioles and alveoli.  Electron microscopy of the substance shows lamellar bodies.  Impaired function of which of the following most likely caused excessive accumulation of the substance in this patient's alveoli?

A) Alveolar macrophages
B) Ciliated airway epithelium
C) Club cells
D) Fibroblasts
E) Type 1 pneumocytes

Correct Answer:

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