45-year Smoking 1 in Medicine / Internal Medicine — 68yo Man | Respiratory / Pulmonology | SMLE Q#11591

A 68-year-old man with a 45-year history of smoking 1.5 packs/day has progressively worsening dyspnea for 2 years and markedly reduced exercise tolerance. He reports a chronic minimally productive cough and unintentional weight loss of 4 kg over 6 months. Examination shows a thin man using accessory muscles, increased anteroposterior chest diameter, decreased breath sounds, diminished diaphragmatic excursion, and hyperresonant percussion without crackles. Spirometry shows an obstructive pattern with markedly reduced FEV1, increased total lung capacity, and reduced DLCO. Which of the following is the most likely diagnosis?