A 68-year-old man presents to the pulmonary clinic complaining of worsening shortness of breath and a dry, hacking cough over the past 8 months. He previously enjoyed walking 2 miles daily but now struggles to walk even half a mile without resting. His symptoms have been insidious, without any acute episodes of fever, chills, or flu-like symptoms. His medical history is significant for hypertension and hyperlipidemia. He is a lifelong nonsmoker. He worked as an accountant before retiring 3 years ago. He moved into an older house 4 years ago and notes a persistent damp smell in the basement. He does not keep birds and has no known exposure to farming or industrial chemicals. His medications include lisinopril and atorvastatin.

He is in mild respiratory distress on exertion but comfortable at rest. He is afebrile. His blood pressure is 132/84 mmHg with a heart rate of 88 bpm. His respiratory rate is 18/min with an oxygen saturation of 94% on room air.