An 83-year-old man with a 20-year history of seropositive rheumatoid arthritis (RA) presented to the emergency department with 2 weeks of progressive dyspnea and dry cough. His arthritis had been treated with leflunomide monotherapy for 4.5 months. His medical history included hypertension. He had quit smoking > 30 years ago and denied recent travel, sick contacts, bird exposure, or suggestive occupational history. His medications included leflunomide, spironolactone, terazosin, and dyazide. He had used methotrexate > 10 years prior but did not recall any particular adverse reaction.