In rare cases, a major difference in blood pressure between arms can be a symptom of a tear in the wall of the aorta. (Canva Image)If you have been taking your blood pressure (BP) reading by strapping your left arm to the device so far, it may cost you nothing to take a second reading by strapping your right arm too. One of my patients, a 37-year-old woman, now knows why this drill matters as she recorded very low BP (70/40 mm Hg) on her left arm during an OPD visit. I did it with a conventional device and also had trouble finding her pulse. But she didn’t experience dizziness or any significant discomfort. In fact, she told me that her BP had never gone higher than 90/60 mm Hg for about a decade and that she had reconciled herself to having a low BP.But just because she seemed normal, I insisted on measuring her BP on the right arm. I was surprised to find that her reading was normal at 110/70 mm Hg. After a gap, I checked the left arm reading again and found it to be hovering at 80/45 mm Hg. She really had a big left arm-right arm discrepancy. A persistent BP difference of more than 10 mm Hg clearly indicates an underlying cardio-vascular condition.What does the difference in BP indicate?This is associated with an increased risk of stroke, heart attack and peripheral artery disease (PAD) — a condition caused by clogged arteries in the limbs. In older adults, it is often linked to plaque buildup in the arteries supplying blood to the arm with the lower reading. This can be an early warning sign of blockages in other critical areas, including the heart and brain. In rare cases, a major difference in blood pressure between arms can be a symptom of a tear in the wall of the aorta.In her case, tests revealed inflammation that had damaged the large artery that carries blood from her heart to the left arm. This inflammation led to the thickening, narrowing or complete blockage of the artery. Sometimes the weakened artery walls may bulge and tear. This condition is known as Takayasu’s arteritis, also known as pulseless disease, where you cannot feel the pulse because of reduced blood flow to the arm. It’s possible for inflammation to damage arteries for years before you realise something is wrong.What causes this blockage in the left arm?No research has found a cause. The condition is likely an autoimmune disease in which your immune system attacks your own arteries by mistake. The disease may be triggered by a virus or other infection.Who is most vulnerable?Women report this the most, it is rare in men. Usually, it happens in women under 40 in India, Japan and southeast Asia.What about diagnosis?If there is differential limb pressure, we check for inflammatory markers in the blood like the ESR (Erythrocyte Sedimentation Rate) test, which measures how quickly red blood cells settle at the bottom of a test tube, with a faster settling rate indicating more inflammation. A CRP test measures C-reactive protein, a substance produced by the liver in response to inflammation in the body. If inflammation is very high, we go for imaging tests like CT angiograms.What about therapy?Story continues below this adThe first line is steroids. Then we administer immunosuppressants as it is an autoimmune condition. If these don’t work, then we administer a new class of drugs called biologics.If women diagnosed with Takayasu’s arteritis are planning on becoming pregnant, they should work with their doctor to limit complications before they conceive. Due to the risk of relapse and progression, patients require monitoring throughout their lives, even during periods of remission.(Dr Tickoo is Director, Internal Medicine, Max Healthcare)© The Indian Express Pvt Ltd