How do we classify peripheral arterial disease?

Classification of Peripheral Arterial Disease

Peripheral arterial disease is classified into four distinct clinical subsets based on symptom presentation: asymptomatic PAD, chronic symptomatic PAD (including claudication), chronic limb-threatening ischemia (CLTI), and acute limb ischemia (ALI). 1

Primary Clinical Classification System

The most current approach recognizes these four clinical subsets, which reflect disease severity and guide treatment urgency 1:

1. Asymptomatic PAD

• Patients have objectively confirmed PAD (ABI <0.90) but report no leg symptoms 1
• Affects 20-59% of patients with proven PAD, depending on the population studied 1
• Critical caveat: Many "asymptomatic" patients have "masked LEAD"—they self-limit activity to avoid symptoms or have reduced pain sensitivity from conditions like diabetic neuropathy 1
• These patients still demonstrate functional impairment comparable to those with claudication and face increased risk of major adverse cardiovascular events and mortality 1

2. Chronic Symptomatic PAD (Claudication)

• Most common clinically evident subset, reported in up to 80% of patients with proven PAD 1
• Characterized by exertional leg symptoms (pain, aching, cramping, fatigue, tingling, numbness, burning) in buttocks, thigh, calf, or foot 1
• Key diagnostic features: symptoms occur consistently during walking, absent at rest, do not improve during continued walking, and resolve within approximately 10 minutes of rest 1
• Anatomic correlation: iliac disease causes hip/buttock/thigh pain; femoral-popliteal disease causes calf pain; tibial disease causes calf or foot pain 1

3. Chronic Limb-Threatening Ischemia (CLTI)

• Defined by chronic (>2 weeks) ischemic rest pain, non-healing wounds/ulcers, or gangrene with objectively proven arterial occlusive disease 1
• This terminology has replaced the older term "critical limb ischemia" (CLI) to emphasize the chronic nature and limb-threatening risk 1
• Typically associated with ankle pressure <50 mmHg or toe pressure <30 mmHg 1
• Rest pain is characteristically located in the foot or toes, experienced when lying down, and severely disrupts sleep 1
• Carries 3-fold increased risk of MI, stroke, and vascular death compared to claudication 1

4. Acute Limb Ischemia (ALI)

• Acute (<2 weeks) hypoperfusion threatening tissue viability 1
• Classic presentation: the "5 Ps"—pain, paralysis, paresthesias, pulselessness, and pallor (some add a sixth "P" for poikilothermia/coldness) 1, 2
• Requires emergent evaluation and prompt revascularization for salvageable limbs 1

Severity Grading Systems

Rutherford Classification (Most Widely Used)

The Rutherford system provides granular severity grading from 0-6 1:

• Category 0: Asymptomatic 1
• Category 1: Mild claudication 1
• Category 2: Moderate claudication 1
• Category 3: Severe claudication 1
• Category 4: Ischemic rest pain (threshold for CLTI) 1
• Category 5: Minor tissue loss 1
• Category 6: Major tissue loss 1

Fontaine Classification (Alternative System)

A simpler four-stage system 1:

• Stage I: Asymptomatic 1
• Stage IIa: Claudication at walking distances >200 meters 1
• Stage IIb: Claudication at walking distances <200 meters 1
• Stage III: Rest pain 1
• Stage IV: Ulceration or gangrene 1

Anatomic Classification

PAD is also classified by anatomic level of disease 1:

• Aortoiliac: Infrarenal abdominal aorta, common iliac, external and internal iliac arteries 1
• Femoropopliteal: Common femoral, profunda femoris, superficial femoral, and popliteal arteries 1
• Infrapopliteal: Tibial-peroneal trunk, anterior tibial, posterior tibial, peroneal, and pedal vessels 1

Patients commonly have multilevel disease across multiple segments 1

Critical Clinical Pitfalls

The "asymptomatic" designation can be misleading—elderly patients with multiple comorbidities, heart failure limiting walking capacity, or diabetic neuropathy may have severe disease without typical symptoms and can present suddenly with toe necrosis after minor trauma 1. These patients require identification through systematic pulse examination and ABI screening, not symptom inquiry alone 1.

Pain intensity varies significantly between patients with similar disease severity, influenced by factors like neuropathy, pain sensitivity, and psychological factors 1. Therefore, classification should integrate objective hemodynamic measures (ABI, toe pressures, TcPO2) with clinical presentation 1.

Patients move between clinical subsets over time—chronic symptomatic PAD can deteriorate to CLTI or ALI, or improve after treatment 1. This dynamic nature requires ongoing surveillance rather than one-time classification 1.