Add to ORKGNo abstract available. Article truncated at 140 words. History of Present Illness A 69 year old woman was seen with a three day history of nonproductive cough and shortness of breath. PMH, SH and FHShe has a past history of atrial fibrillation and hypothyroidism. Her present medications include:•Diltiazem•Amiodarone•Aspirin•Levothyroxine•Multi vitaminsThere is a 20 pack-year smoking history but she quit in 1998. She is employed as a law school professor. Physical ExaminationHer physical examination is normal. Chest X-rayHer admission chest x-ray is shown in Figure 1. Figure 1. Chest x-ray showing the PA (Panel A) and lateral (Panel B) views. An electrocardiogram showed normal sinus rhythm. Which of the following is the most likely cause o...