His temperature was 36.1°C, BP was 135/60 mm Hg, heart rate was 88 beats/min, respiratory rate was 18 breaths/min, and oxygen saturation was 98% on ambient air. His examination was notable for decreased breath sounds at the lung bases bilaterally, with scant inspiratory crackles at the left base. He did not have audible wheezes, rhonchi, or squeaks. Initial laboratory findings, including results of a complete blood count and comprehensive metabolic panel, were normal. Blood, urine, and sputum cultures were negative. Tests for HIV antibody, cryptococcal antigen, urine histoplasma antigen, cocciodiodes antibody, and blastomycosis antibody were negative. Serologic testing for rheumatologic disease was negative, including antinuclear antibody, rheumatoid factor, antineutrophil cytoplasmic antibody, and myositis antibodies. Bronchoscopy findings with BAL did not indicate infection. Transbronchial biopsy specimens revealed intraalveolar accumulation of histiocytes with focal organizing lung injury. Specimens from a surgical lung biopsy, performed to rule out malignancy, revealed multiple foci of organizing pneumonia with associated small nonnecrotizing granulomata (Fig 2A), as well as an organizing pleuritis (Fig 2B). The biopsy specimen observations and clinical picture were most consistent with BOOP.