Definitions of PAD, CLI, and ALI
Peripheral Artery Disease (PAD)
PAD is atherosclerotic disease of the lower extremity arteries affecting the aortoiliac, femoropopliteal, and infrapopliteal arterial segments. 1
- PAD affects 10 to 12 million individuals in the United States over age 40 and is associated with significant morbidity, mortality, and quality of life impairment. 1
- The disease encompasses a spectrum from asymptomatic to claudication to chronic limb-threatening ischemia. 1
- Claudication is the hallmark symptom: fatigue, cramping, aching, pain, or discomfort of vascular origin in lower extremity muscles that is consistently induced by walking and consistently relieved by rest (usually within approximately 10 minutes). 1
- Most patients with confirmed PAD do not have typical claudication but present with atypical leg symptoms or are asymptomatic. 1
Critical Limb Ischemia (CLI) / Chronic Limb-Threatening Ischemia (CLTI)
CLI (now termed CLTI) is a chronic condition (>2 weeks duration) characterized by ischemic rest pain, nonhealing wounds/ulcers, or gangrene attributable to objectively proven arterial occlusive disease. 1
Key Diagnostic Features:
- Chronicity is essential: Symptoms must persist for more than 2 weeks to distinguish from acute limb ischemia. 1
- The diagnosis requires both clinical symptoms AND objective arterial disease confirmation via ankle-brachial index (ABI), toe-brachial index (TBI), transcutaneous oxygen pressure (TcPO₂), or skin perfusion pressure. 1, 2
- A very low ABI or TBI alone does not establish CLI—the constellation of symptoms and objective findings is required. 1, 2
Clinical Presentations:
- Ischemic rest pain: Typically worse when supine and may improve with limb dependency. 2
- Tissue loss: Minor (nonhealing ulcer, focal gangrene with diffuse pedal ischemia) or major (extending above transmetatarsal level). 1, 2
- Gangrene: Focal or diffuse tissue necrosis. 1, 2
Objective Criteria:
- ABI typically <0.4 in nondiabetic individuals. 2
- Absolute ankle pressure ≤50 mmHg or toe pressure ≤30 mmHg often indicates severe ischemia requiring revascularization to prevent amputation. 2
- TBI may be more reliable in patients with noncompressible vessels (common in diabetes). 2
Important Clinical Pitfall:
- Diabetic patients may present with severe CLI and tissue loss but minimal pain due to concomitant neuropathy, making diagnosis more challenging. 2
- CLI should be suspected in any diabetic individual with known lower extremity PAD, regardless of ABI value. 2
Nomenclature Evolution:
- Current terminology has evolved from "Critical Limb Ischemia (CLI)" to "Chronic Limb-Threatening Ischemia (CLTI)" to emphasize the chronic nature, limb-threatening potential with amputation risk, and distinction from acute limb ischemia. 1
Acute Limb Ischemia (ALI)
ALI is acute hypoperfusion of the limb (≤2 weeks duration) that may be characterized by the "6 Ps": pain, pallor, pulselessness, poikilothermia (cold), paresthesias, and/or paralysis. 1
Rutherford Classification System:
ALI is further classified into three categories based on limb viability: 1
Category I (Viable): Limb not immediately threatened; no sensory loss; no muscle weakness; audible arterial and venous Doppler signals. 1
Category II (Threatened): Mild-to-moderate sensory or motor loss; inaudible arterial Doppler; audible venous Doppler.
Category III (Irreversible): Major tissue loss or permanent nerve damage inevitable; profound sensory loss (anesthetic); profound muscle weakness or paralysis (rigor); inaudible arterial and venous Doppler signals. 1
Critical Distinguishing Feature from CLI/CLTI:
- Time course is the key differentiator: ALI is acute (<2 weeks) versus CLI/CLTI which is chronic (>2 weeks). 1, 2
- ALI typically presents with the classic "6 Ps" whereas CLI/CLTI presents with chronic rest pain, wounds, or gangrene. 2
- Patients at risk for CLI who develop acute limb symptoms represent potential vascular emergencies and require immediate assessment. 2