What is Peripheral Arterial Disease (PAD)?
Peripheral arterial disease (PAD) is atherosclerotic narrowing or blockage of the arteries supplying the lower extremities, diagnosed by an ankle-brachial index (ABI) ≤0.90, and represents a marker of systemic atherosclerosis that dramatically increases the risk of myocardial infarction, stroke, amputation, and death. 1, 2
Definition and Pathophysiology
PAD is primarily caused by atherosclerotic plaque progressively occluding the arterial lumen of the lower extremities 3, 4. The disease affects approximately 230 million people worldwide, with prevalence reaching 10-20% in adults over 65 years and up to 29% in high-risk populations aged 50-69 with smoking or diabetes 1, 5, 4.
The critical point: PAD is not just a leg problem—it's a cardiovascular disease equivalent. Patients with PAD face 3-6 times higher risk of cardiovascular death compared to those without PAD 6, 2.
Clinical Presentations
PAD manifests in four distinct clinical subsets 2, 7:
1. Asymptomatic PAD (40-50% of cases)
- No leg symptoms but may have functional impairment
- Detected by abnormal ABI or absent pulses
- Often "masked" by reduced walking capacity from other conditions 1, 7
2. Chronic Symptomatic PAD/Intermittent Claudication (only 10-11% present classically)
Classic claudication has three features 1:
- Muscle cramping pain (typically calf) distal to arterial stenosis
- Pain develops only with exercise
- Pain resolves within 10 minutes of rest
Common pitfall: Only 5-10% present with classic claudication symptoms. Most patients (70-80%) have atypical leg pain, nonspecific discomfort, or are completely asymptomatic 1, 8, 9.
3. Chronic Limb-Threatening Ischemia (CLTI)
4. Acute Limb Ischemia
- Requires urgent evaluation to preserve limb viability 10
Diagnosis
The ankle-brachial index (ABI) is the primary diagnostic test 1, 11:
- ABI ≤0.90 = PAD diagnosis confirmed (95% sensitive and specific) 1, 11
- ABI 0.91-0.99 = Borderline; consider exercise ABI if symptomatic 2
- ABI >1.30-1.40 = Non-compressible vessels (common in diabetes/chronic kidney disease); use toe-brachial index or other tests 3, 7, 10
Exercise ABI: If resting ABI is normal but clinical suspicion remains high, perform post-exercise ABI. A >20% decrease confirms PAD 3, 7.
Risk Factors
The major atherosclerotic risk factors apply 3:
- Cigarette smoking
- Diabetes mellitus
- Dyslipidemia
- Hypertension
- Hyperhomocysteinemia
- Age ≥70 years or age 50-69 with smoking/diabetes 3
Physical Examination Findings
Key findings to document 3:
- Pulse assessment (0=absent, 1=diminished, 2=normal, 3=bounding) at brachial, radial, femoral, popliteal, dorsalis pedis, posterior tibial sites
- Femoral bruits on auscultation
- Foot inspection: color, temperature, skin integrity, ulcerations
- Signs of severe PAD: distal hair loss, trophic skin changes, hypertrophic nails
Cardiovascular Risk
Critical understanding: Cardiovascular ischemic events (MI, stroke) are MORE frequent than limb events in PAD patients, regardless of symptom status 3. This is why aggressive cardiovascular risk reduction is paramount—PAD patients have concomitant coronary and cerebrovascular disease in the majority of cases 3.
Non-Atherosclerotic Causes
While atherosclerosis dominates, PAD can also result from 3:
- Thromboembolism
- Inflammatory arteritides
- Trauma
- Adventitial cysts or entrapment syndromes
- Congenital abnormalities
- Aneurysmal disease
Screening Recommendations
Who should be screened 3:
- Age <50 with diabetes AND one other atherosclerosis risk factor
- Age 50-69 with smoking or diabetes history
- Age ≥70 (all patients)
- Any age with leg symptoms, abnormal pulses, or known atherosclerotic disease elsewhere
Underdiagnosis Problem
Major clinical gap: In the PARTNERS study, 55% of PAD cases were newly diagnosed, and only 49% of physicians were aware of their patients' PAD diagnosis despite 83% of patients knowing they had it 9. This underdiagnosis leads to inadequate cardiovascular risk management and worse outcomes 9, 12.
Health Disparities
The 2024 guidelines emphasize: Clinicians must actively pursue evidence of health disparities in PAD diagnosis, treatment, and outcomes, as these disparities are associated with poor limb and cardiovascular outcomes 2, 7.