Final answer:
Clubbing and sudden joint pain in a chronic smoker most likely suggest lung cancer, especially when coupled with a history of smoking and the presence of systemic symptoms that are characteristic of paraneoplastic syndromes.
Step-by-step explanation:
If you see clubbing and sudden onset joint pain in a chronic smoker, you should suspect lung cancer. Clubbing, which is the swelling of the fingers and toes with certain characteristic changes, can sometimes be associated with lung cancer. Chronic smokers are at a higher risk for developing lung cancer, and paraneoplastic syndromes associated with lung cancer can include symptoms like clubbing and hypertrophic pulmonary osteoarthropathy, which can manifest as joint pain.
Lung cancer can also cause non-specific symptoms such as fatigue, weight loss, and anorexia, and it's the presence of these systemic symptoms along with a history of smoking that would steer a clinician toward considering lung cancer over joint-specific diseases like rheumatoid arthritis or gout.