What are the signs and symptoms of critical limb ischemia?

Signs and Symptoms of Critical Limb Ischemia

Critical limb ischemia (CLI) is characterized by chronic (≥2 weeks) ischemic rest pain, nonhealing wounds/ulcers, or gangrene in one or both legs attributable to objectively proven arterial occlusive disease. 1

Clinical Presentation

Primary Symptoms

• Ischemic rest pain - typically worse when supine (e.g., in bed) and may lessen when the limb is in a dependent position 1
• Nonhealing wounds or ulcers 1
• Gangrene (focal or diffuse) 1

Physical Examination Findings

• Tissue loss - may be minor (nonhealing ulcer, focal gangrene with diffuse pedal ischemia) or major (extending above transmetatarsal level) 1
• Diminished or absent pulses in affected extremity 1
• Pallor of the affected limb, especially when elevated 1
• Cold extremity (poikilothermia) compared to the contralateral limb 1
• Dependent rubor (redness when limb is in dependent position) 1
• Trophic skin changes (thin, shiny skin; loss of hair; thickened nails) 1

Distinguishing Features from Acute Limb Ischemia

CLI must be distinguished from acute limb ischemia (ALI), which presents differently:

• CLI is chronic (≥2 weeks duration) whereas ALI is acute (<2 weeks) 1
• ALI presents with the classic "6 Ps": pain, pallor, pulselessness, poikilothermia (cold), paresthesias, and paralysis 1
• ALI often has a sudden onset with rapid progression, while CLI develops more gradually 1

Objective Diagnostic Criteria

The diagnosis of CLI requires both symptoms and objective evidence of arterial occlusive disease:

• Ankle-Brachial Index (ABI) typically <0.4 in nondiabetic individuals 1
• Toe-Brachial Index (TBI) may be more reliable in patients with noncompressible vessels 1
• Transcutaneous oxygen pressure (TcPO₂) measurements 1
• Skin perfusion pressure measurements 1
• Absolute ankle pressure ≤50 mmHg or toe pressure ≤30 mmHg often indicates severe ischemia that may require amputation if not revascularized 1

Risk Factors That Increase Severity

Several factors can increase the risk of limb loss in patients with CLI:

Factors that reduce blood flow to the microvascular bed:

• Diabetes 1
• Severe renal failure 1
• Severely decreased cardiac output (severe heart failure or shock) 1
• Vasospastic diseases (e.g., Raynaud's phenomenon) 1
• Smoking and tobacco use 1

Factors that increase demand for blood flow:

• Infection (e.g., cellulitis, osteomyelitis) 1
• Skin breakdown or traumatic injury 1

Clinical Implications

• CLI represents a medical emergency with high risk of limb loss if not promptly treated 2, 3
• Patients with CLI have a 3-fold higher risk of future myocardial infarction, stroke, and vascular death compared to patients with intermittent claudication 3
• The quality of life for patients with severe CLI can be worse than that of patients with terminal cancer 1
• Without revascularization, CLI patients are at high risk for limb loss and potentially fatal complications from progression of gangrene and development of sepsis 2

Common Pitfalls and Caveats

• A very low ABI or TBI alone does not necessarily mean the patient has CLI - the diagnosis requires both symptoms and objective evidence of arterial disease 1
• Diabetic patients may present with severe CLI and tissue loss but minimal pain due to concomitant neuropathy 1
• CLI should be suspected in any diabetic individual with known lower extremity PAD, regardless of ABI 1
• Patients with CLI and features suggesting atheroembolization should be evaluated for aneurysmal disease (e.g., abdominal aortic, popliteal, or common femoral aneurysms) 1
• Patients at risk for CLI (those with diabetes, neuropathy, chronic renal failure, or infection) who develop acute limb symptoms represent potential vascular emergencies and should be assessed immediately 1