Final answer:
Leg pain worsening at night in a smoker is likely related to Peripheral artery disease (PAD), due to the narrowing of arteries from atherosclerosis, exacerbated by the patient's smoking history.
Step-by-step explanation:
The subject of this question is Medicine, and it pertains to differentiating between causes of leg pain in a patient with a substantial smoking history. Leg pain that worsens at night in a 60-pack-year-old smoker could be suggestive of numerous conditions. However, given the history of smoking and the typical profile, Peripheral artery disease (PAD) is of high concern. PAD is caused by the narrowing of the peripheral arteries, typically in the legs due to atherosclerosis, and it can result in intermittent pain which is characteristic of the condition known as intermittent claudication. This pain is generally experienced when walking and tends to resolve with rest but may also worsen at night. It's also important to note that patients with a history of smoking have a higher risk of developing PAD due to the detrimental effects of tobacco on the vascular system, including contributing to the development of plaque in the arteries.