What are the differential diagnoses for a persistent inter‑arm systolic blood‑pressure difference ≥10 mm Hg?

Differential Diagnosis for Persistent Inter-Arm Systolic Blood Pressure Difference ≥10 mm Hg

A persistent inter-arm systolic blood pressure difference ≥10 mm Hg requires systematic evaluation to distinguish between benign physiologic variation (present in approximately 20% of normal individuals) and pathologic vascular disease, with differences ≥15-20 mm Hg strongly indicating arterial obstruction that demands urgent vascular imaging. 1, 2

Measurement-Related Causes (Must Exclude First)

Before pursuing pathologic diagnoses, confirm the finding with proper technique, as technical errors are the most common cause of apparent inter-arm differences:

• Improper arm positioning: Each inch above or below heart level (mid-sternum/fourth intercostal space) alters systolic pressure by approximately 2 mm Hg, creating artificial differences ≥10 mm Hg 2, 3
• Mismatched cuff sizes: Using cuffs that are not at least 40% of arm circumference or different sizes between arms generates false pressure gradients 2, 3
• Unsupported arms: Having the patient hold their arm up causes isometric muscle contraction that falsely elevates readings 2, 3
• Sequential measurement variability: Normal beat-to-beat blood pressure variation can produce transient differences; simultaneous bilateral measurement is preferred when available 2, 4

Critical action: Repeat measurements with both arms at heart level, fully supported, using appropriately sized cuffs after 5 minutes of rest to confirm persistence of the difference 1, 2

Physiologic Variation (Benign)

• Normal inter-arm asymmetry: Mean absolute differences of 3-6 mm Hg for systolic and 2-5 mm Hg for diastolic pressure occur in healthy individuals 5, 4
• Prevalence of ≥10 mm Hg difference: Present in 18-20% of asymptomatic hypertensive and normotensive individuals without vascular disease 6, 4
• Anatomic dominance: Slight differences in arterial geometry and stiffness between arms can produce measurable but clinically insignificant pressure gradients 7

Key threshold: Differences of 10-14 mm Hg warrant documentation and use of the higher-reading arm for future measurements, but do not automatically indicate pathology if confirmed measurements remain <15 mm Hg 1, 2

Pathologic Vascular Causes (Require Urgent Evaluation)

When the difference is ≥15-20 mm Hg or accompanied by vascular signs, consider:

Upper Extremity Arterial Obstruction

• Subclavian artery stenosis: The most common pathologic cause of significant inter-arm differences, creating a pressure gradient across the narrowed vessel 2
• Innominate (brachiocephalic) artery stenosis: Particularly when the right arm shows lower pressure, as this vessel supplies both right subclavian and right carotid arteries 2
• Complete subclavian occlusion: May render one arm completely unmeasurable with absent pulses 2

Vascular examination findings: Diminished or absent brachial/radial pulses in the lower-pressure arm, supraclavicular/infraclavicular bruits, pulse delay between arms, signs of arm claudication or ischemia 2

Aortic Pathology

• Aortic coarctation: Especially in younger patients; may present with upper-extremity hypertension and lower-extremity hypotension 2
• Aortic dissection: Medical emergency—suspect when difference ≥20 mm Hg occurs with acute chest pain, back pain between shoulder blades, syncope, or neurological symptoms 2

Large Vessel Vasculitis

• Takayasu arteritis: Inflammatory stenosis of aortic arch branches, more common in young women 2
• Giant cell arteritis: Consider in patients >50 years with systemic inflammatory symptoms 2

Laboratory clues: Elevated ESR and CRP suggest inflammatory vasculitis 2

Diagnostic Algorithm

Step 1: Confirm the Finding

• Remeasure bilaterally with proper technique (both arms at heart level, appropriately sized cuffs, fully supported, after 5-minute rest) 1, 2
• If difference persists ≥10 mm Hg, document which arm is higher and use that arm for all future measurements 1, 3

Step 2: Focused Vascular Examination

• Palpate bilateral brachial, radial, and ulnar pulses; grade quality (0-3 scale) 2
• Auscultate supraclavicular, infraclavicular, carotid, and femoral regions for bruits 2
• Assess for signs of limb ischemia (pallor, coolness, muscle atrophy) 2
• Check for symptoms of subclavian steal (dizziness, vertigo, ataxia with arm use) 2

Step 3: Risk Stratification by Magnitude

Difference 10-14 mm Hg:

• Document finding and use higher-reading arm for ongoing management 1
• Perform ankle-brachial index (ABI) using the higher arm pressure as denominator; ABI <0.9 increases suspicion for concurrent upper-extremity disease 8
• Consider duplex ultrasound of subclavian/axillary arteries if vascular examination is abnormal 2

Difference ≥15-20 mm Hg:

• Definitively abnormal—strongly suggests arterial pathology 2
• Order duplex ultrasound of subclavian and axillary arteries as first-line imaging 2
• If ultrasound equivocal or clinical suspicion for aortic pathology, obtain CT angiography or MR angiography of aortic arch and great vessels 2
• Refer to vascular surgery or cardiology for further management 2

Difference ≥20 mm Hg with acute symptoms (chest pain, back pain, syncope, neurological deficits):

• Medical emergency—obtain immediate CT angiography to exclude aortic dissection 2
• Do not delay imaging for additional testing 2

Step 4: Associated Cardiovascular Evaluation

• Patients with confirmed subclavian stenosis have high prevalence of coronary artery disease; perform ECG and cardiac risk assessment 2
• An inter-arm difference ≥10 mm Hg is independently associated with increased cardiovascular mortality and peripheral artery disease 9

Critical Pitfalls to Avoid

• Do not dismiss a 10-14 mm Hg difference as "normal variation" without proper confirmation with repeat measurements using correct technique 2, 6
• Do not use the lower-reading arm for hypertension management, as this leads to systematic underestimation of true blood pressure and undertreatment 1, 2
• Do not fail to pursue urgent vascular imaging when the difference is ≥20 mm Hg, even in asymptomatic patients, as this strongly indicates clinically significant arterial disease 2
• Do not use different cuff sizes or measurement techniques between arms during confirmation, as this creates artificial differences 2, 3
• Do not overlook the need for emergency evaluation when large differences occur with acute symptoms (chest pain, syncope, neurological deficits), as aortic dissection carries high mortality if missed 2

Management Implications

• Always use the arm with the higher systolic pressure for all subsequent blood pressure measurements and treatment decisions to avoid underdiagnosis and undertreatment of hypertension 1, 2, 3
• Asymptomatic chronic subclavian stenosis may be managed conservatively with medical therapy if collateral circulation is adequate, but symptomatic patients (arm claudication, subclavian steal syndrome) require revascularization 2
• Document the higher-reading arm prominently in the medical record to ensure consistency across providers 2, 3