A 36-year-old woman presents with dry cough and dyspnea on exertion, which have progressed over the past 2 years. She is dyspneic after climbing two flights of stairs. This surprises her because she was able to run an 8-min mile 2 years ago. She does not have wheezing, fever, chills, weight loss, skin rash, or joint pain, but she does have conjunctival injection. She is a life-long nonsmoker and has no pets. She does not have any history of asbestos exposure and works as a diamond polisher for a large-volume diamond buyer. Physical examination shows mild clubbing, conjunctival injection, and dry crackles bilaterally in the lower third of the lung fields. She does not have hepatosplenomegaly or a skin rash. Her chest radiograph is shown in Figure 1
. Pulmonary function tests show FVC of 2.67 L (60% of predicted), FEV1 of 2.35 L (63% of predicted), and oxygen saturation by pulse oximetry of 93% at rest and 87% after walking 300 feet in 3 min. Bronchoscopy with BAL and transbronchial lung biopsy are performed. A few hours later, the pathologist calls to report bizarre-appearing, multinucleated giant cells with a cell within a cell, or a “cannibalistic” appearance in the BAL specimen (Fig 2
). Which of the following diseases is most likely?