An 84-year-old man presented to the ED with acute-onset shortness of breath. He denied cough, sputum production, hemoptysis, wheezing, pleuritic chest pain, fever, leg pain or swelling. He was active and in his normal state of health until the onset of this acute episode of dyspnea. He did not have a history of a recent hospitalization, surgery, or long travel. He denied chronic respiratory symptoms before the current episode. His medical history was unremarkable except for hypothyroidism for which he was taking levothyroxine. The patient had no history of pulmonary TB or fungal infection. He had a 5-pack-year smoking history and quit before age 40 years. He worked as a dental technician for > 40 years.