Figure 1. A 26-year-old man presented with nonproductive cough and exertional dyspnea. Physical examination disclosed acrocyanosis. Chest radiography showed patchy alveolar and interstitial disease in a perihilar “batwing” distribution (Panel A). High-resolution computed tomography of the chest (Panel B) revealed extensive bilateral air-space disease (arrows) and a “crazy paving” appearance within the affected air spaces (arrowheads). Pulse oximetry revealed oxyhemoglobin desaturation to 79 percent when the patient was walking. Pulmonary-function testing demonstrated a moderate restrictive ventilatory defect and severe reduction in lung volumes and diffusion capacity. Fiberoptic bronchoscopy with transbronchial lung biopsies showed alveolar filling with amorphous, granular eosinophilic material . . .