What diagnosis explains high blood pressure in the right arm and both legs with low blood pressure in the left arm?

Aortic Coarctation or Aortic Arch Syndrome (Takayasu Arteritis)

The most likely diagnosis is aortic coarctation or aortic arch syndrome (such as Takayasu arteritis), which characteristically presents with lower blood pressure in the left upper extremity compared to the right arm and both legs.

Diagnostic Reasoning

This blood pressure pattern—elevated in the right arm and both legs but reduced in the left arm—is pathognomonic for obstruction of the left subclavian artery or involvement of the aortic arch affecting left-sided vessels. The key clinical guidelines emphasize:

Critical Diagnostic Features

Inter-arm blood pressure difference >15-20 mmHg is abnormal and highly suggestive of subclavian or innominate artery stenosis 1. In your case, the left arm shows significantly lower pressure, indicating left subclavian artery involvement.

• In children specifically, the right arm is the preferred location for BP measurement because of the possibility of coarctation of the aorta, which might result in an erroneously low BP measurement in the left arm 2
• Guidelines mandate measuring BP in both arms simultaneously at first visit, and when there's a consistent difference, use the arm with higher BP for ongoing monitoring 3

Why Both Legs Are Also Elevated

The preserved or elevated blood pressure in both lower extremities distinguishes this from:

• Subclavian steal syndrome alone (which wouldn't elevate leg pressures)
• Peripheral arterial disease (which would reduce leg pressures, not elevate them)

When leg pressures are higher than or equal to arm pressures, this suggests:

1. Aortic coarctation: Obstruction typically occurs distal to the left subclavian artery origin, causing reduced flow to the left arm while maintaining high pressure below the coarctation (both legs)
2. Aortic arch syndrome: Inflammatory or atherosclerotic disease affecting the arch vessels, particularly the left subclavian artery origin

Immediate Diagnostic Workup

Physical examination must include 4, 1:

• Palpation of all four extremity pulses (brachial, radial, femoral, dorsalis pedis, posterior tibial)
• Auscultation for bruits: precordial, chest, and abdominal murmurs suggesting aortic coarctation or aortic disease 4
• Assessment for diminished and delayed femoral pulses compared to brachial pulses (classic for coarctation) 4
• Check for radiofemoral delay

Confirmatory imaging required 5, 6:

• CT angiography or MR angiography of the aortic arch to identify:
  • Coarctation site and severity
  • Left subclavian artery stenosis or occlusion
  • Aortic arch vessel involvement
  • Signs of Takayasu arteritis (wall thickening, inflammation)

Age-Dependent Considerations

• If patient is a child or young adult: Congenital aortic coarctation is most likely, often associated with bicuspid aortic valve 6
• If patient is middle-aged or older: Consider acquired causes:
  • Takayasu arteritis (more common in women <40 years)
  • Atherosclerotic disease of aortic arch vessels
  • Giant cell arteritis (if >50 years old)

Critical Pitfalls to Avoid

1. Do not assume essential hypertension when there's significant inter-arm BP difference—this pattern demands vascular imaging 1
2. Do not measure BP only in one arm going forward—the higher reading (right arm) should be used for hypertension management 1
3. Do not delay imaging if clinical suspicion is high—acute aortic dissection can present similarly and requires emergency intervention 6, 7

Acute Aortic Dissection Must Be Excluded

While less likely given the specific pattern (both legs elevated), acute aortic dissection can present with inter-arm BP differences 6, 7:

• Type A dissection characteristically shows left arm BP > right arm BP with low right arm pressure (opposite of your case) 7
• Your pattern (low left, high right and legs) is more consistent with chronic obstruction
• However, if patient has acute chest/back pain, emergency CT angiography is mandatory 6, 8

Next Steps Algorithm

1. Immediate: Four-limb BP measurement with proper technique (patient supine, 5-10 minutes rest) 9
2. Urgent: Auscultation for murmurs and pulse examination of all extremities 4, 1
3. Definitive: CT or MR angiography of entire aorta and arch vessels 5, 6
4. If coarctation confirmed: Cardiology/vascular surgery referral for intervention consideration
5. If inflammatory arteritis suspected: ESR, CRP, and rheumatology consultation

The combination of low left arm BP with elevated right arm and bilateral leg BPs is virtually diagnostic of left subclavian artery obstruction with preserved distal aortic flow, most commonly from coarctation or aortic arch syndrome.