Differential Diagnosis

• Single most likely diagnosis
  • Emphysema: The patient's 50 pack-year history of cigarette smoking, symptoms of worsening dyspnea on exertion, and physical examination findings of cachexia, moderate respiratory distress, and pursed-lip breathing are highly suggestive of emphysema. The prolonged expiratory phase of respiration and decreased breath sounds also support this diagnosis.
• Other Likely diagnoses
  • Chronic bronchitis: Although the patient stopped smoking 2 weeks earlier, his long history of smoking and symptoms of a dry, hacking cough and dyspnea on exertion could also be consistent with chronic bronchitis.
  • Bronchiectasis: This condition can also present with chronic cough and dyspnea, although it is less likely given the patient's smoking history and lack of other suggestive symptoms such as hemoptysis or recurrent infections.
• Do Not Miss
  • Pulmonary fibrosis: Although less likely, pulmonary fibrosis can present with progressive dyspnea and cough, and it is essential to consider this diagnosis to avoid missing a potentially treatable condition.
  • Lung cancer: Given the patient's significant smoking history and recent onset of symptoms, lung cancer must be considered, especially if there are any "red flag" symptoms such as hemoptysis, weight loss, or chest pain.
• Rare diagnoses
  • Sarcoidosis: This condition can present with respiratory symptoms, but it is less likely given the patient's smoking history and lack of other suggestive symptoms such as skin lesions, eye involvement, or lymphadenopathy.
  • Other rare conditions: Such as lymphangitic carcinomatosis, pulmonary lymphoma, or cystic fibrosis, although these are highly unlikely given the patient's presentation and history.