A patient has a blood pressure of 160/100 in the right arm and 105/65 in the left arm with a heavy smoking history. What is the most likely diagnosis?

• A. Renal Artery Stenosis
• B. Subclavian Steal Syndrome Due to Atherosclerosis
• C. Aortic Dissection
• D. Peripheral Artery Disease

Answer: (B)

A large difference in blood pressure between the arms points to a blockage in the artery supplying the higher-pressure arm, most commonly a stenosis of the subclavian artery on that side. Here the right arm reads 160/100 while the left is 105/65, and the patient has a heavy smoking history, which strongly suggests atherosclerosis. When the subclavian artery proximal to the vertebral artery origin is narrowed, distal pressure falls in that arm. To compensate, blood can be shunted from the vertebral (posterior circulation) toward the affected arm, creating retrograde flow in the vertebral artery—a phenomenon known as subclavian steal. This not only lowers the left arm pressure but can also cause vertebrobasilar (brainstem/cerebellar) symptoms, especially with arm activity.

The other conditions don’t fit this pattern. Renal artery stenosis mainly causes systemic hypertension rather than a marked inter-arm pressure difference. Aortic dissection can cause unequal BP between arms but typically presents with sudden, severe chest or back pain and a tearing sensation. Peripheral artery disease involves the limbs, usually the legs, with claudication and diminished distal pulses there rather than a isolated, large arm BP discrepancy.