A 68-year-old man with chronic obstructive pulmonary disease (COPD) comes to the clinic due to a 9-kg (20-lb) weight loss over the last 2 years. He describes his appetite as "all right" but does say that he is eating less. The patient reports poor taste, fatigue, chronic dyspnea, productive cough, and occasional nausea. He also reports insomnia most nights of the week with poor concentration during the day. He has no night sweats, fevers, chills, dysphagia, change in bowel habits, blood in the stool, or dysphoria. He has had 3 hospitalizations for COPD exacerbation over the past 2 years during which he was treated with short courses of prednisone. The patient has smoked 2 packs of cigarettes daily for 42 years. He reports feeling "bad" for smoking all these years and is trying to quit but says, "It's just very hard." The patient lives alone and often feels lonely. His other medical problems include hypertension and hyperlipidemia. His last colonoscopy was 5 years ago and included removal of 2 hyperplastic polyps. He does not use alcohol or recreational drugs. Family history is not significant. Temperature is 36.7 C (98 F), blood pressure is 130/80 mm Hg, pulse is 80/min, and respirations are 18/min. BMI is 17 kg/m2. Pulse oximetry shows 91% on ambient air. Physical examination reveals moist mucous membranes, normal jugular venous pressure, and distant S1 and S2. Lung examination reveals prolonged expiration, increased resonance to percussion bilaterally, and increased anterior-to-posterior diameter of the chest. The abdomen is soft and nontender. There is no hepatomegaly, splenomegaly, or masses. Testing of the stool for occult blood is negative. No edema or lymphadenopathy is present. Neurologic examination is within normal limits. The patient's affect is normal. Laboratory results are as follows: Chest x-ray reveals hyperexpansion of bilateral lung fields with diaphragmatic flattening. Which of the following is the most likely cause of this patient's weight loss?
B)Chronic lung disease
D)Major depressive disorder