We evaluated a 49-year-old woman who had worsening shortness of breath, non-productive cough and recurrent low-grade fevers over 6 months despite several courses of antibiotics. Her medical history was remarkable for suspected immunodeficiency that had been treated with intravenous immunoglobulin and recurrent pneumonia, including methicillin-resistant Staphylococcus aureus empyema requiring left decortication 2 years earlier. Repeated CT scans of her lung showed progressive patchy ground-glass and consolidative opacities bilaterally with septal prominence (figure 1A).

We performed bronchoscopy. Bronchoalveolar lavage cultures and special stains for bacteria, acid-fast bacilli and fungi were negative. Transbronchial biopsies revealed clusters of alveolar macrophages with …