Chronic Limb Ischaemia

The Concept

Chronic limb ischaemia is a persistent reduction in the arterial blood supply to a limb, almost always caused by atherosclerosis of the lower-limb arteries. It represents a spectrum of severity — from pain only on exertion (intermittent claudication) at the mild end, through pain at rest, to tissue loss (critical limb ischaemia) at the severe end. Understanding it as a supply-versus-demand problem that worsens as the arteries narrow makes the whole clinical picture logical.

Pathophysiology & Risk Factors

Atherosclerotic plaques narrow the arteries (aorto-iliac, femoro-popliteal, and tibial segments), reducing perfusion. When demand exceeds the limited supply on exercise, ischaemic muscle pain (claudication) occurs; as disease progresses, the supply is inadequate even at rest. The risk factors are those of atherosclerosis generally: smoking (the strongest), diabetes, hypertension, hyperlipidaemia, increasing age and male sex.

Clinical Features — the Fontaine Classification

Severity is graded by the Fontaine classification:

Critical limb ischaemia is defined as rest pain for more than 2 weeks, ulceration or gangrene, and is limb-threatening.

Examination

Signs of chronic ischaemia include absent or weak peripheral pulses, a cold and pale limb, hair loss, thin shiny skin, slow capillary refill, and arterial ulcers (painful, 'punched-out', on pressure points and toes). Buerger's test is positive — the leg goes pale on elevation (a low 'Buerger's angle' indicating poor perfusion) and shows reactive hyperaemia (a dusky red colour) on dependency.

Investigation & Management

The key bedside investigation is the ankle-brachial pressure index (ABPI): normal is ~1.0, <0.9 indicates pad, and <0.5 indicates critical ischaemia — but it can be falsely high in diabetics because of calcified, incompressible vessels. Duplex ultrasound and CT/MR angiography map the disease before intervention. Management combines:

• Risk-factor modification — above all smoking cessation, plus control of diabetes, blood pressure and lipids (a statin), and an antiplatelet agent (aspirin or clopidogrel).
• Supervised exercise therapy for claudication (promotes collateral flow).
• Revascularisation — angioplasty ± stenting or bypass surgery — for critical ischaemia or severely disabling claudication.
• Amputation for an unsalvageable limb.

Arterial VS Venous Ulcers — the Key Contrast

A favourite exam distinction is between arterial and venous leg ulcers, and it follows from their pathology. An arterial (ischaemic) ulcer is painful, 'punched-out' with a well-defined edge, and lies over pressure points or the toes/heel, on a cold leg with absent pulses and a low ABPI. A venous ulcer is relatively painless, shallow with sloping edges, and lies in the 'gaiter area' around the medial malleolus, on a warm leg with skin changes of venous insufficiency and a normal ABPI. Getting this contrast right determines whether compression (safe for venous, dangerous for arterial) can be used.

Buerger's Test Explained

Buerger's test is a valuable bedside sign worth understanding. The leg is elevated, and the angle at which it turns pale (the Buerger's angle) indicates the severity of ischaemia — a low angle (the leg going white when only slightly raised) means poor perfusion. The leg is then hung down over the edge of the couch: in significant ischaemia it turns first blue, then a dusky reactive hyperaemic red, as the ischaemic tissue reperfuses. A positive test confirms significant arterial insufficiency.

Prognosis & the Systemic Picture

It is important to appreciate that pad is a marker of widespread atherosclerosis: a patient with limb ischaemia very often has coronary and cerebrovascular disease too, so their main risk is actually myocardial infarction and stroke. This is why 'best medical therapy' (antiplatelet, statin, blood-pressure and diabetes control, smoking cessation) is prescribed not just to save the leg but to reduce cardiovascular death — reframing claudication as a whole-body cardiovascular problem rather than a purely local one.

A Note on the Abpi Pitfall in Diabetes

One practical pitfall deserves emphasis: in diabetic patients (and those with chronic kidney disease), the tibial arteries are often calcified and incompressible, so the cuff cannot occlude them and the ABPI reads falsely high or normal despite significant ischaemia. In these patients the ABPI is unreliable, and the circulation is better assessed with toe pressures (the digital vessels are usually spared calcification) or the Doppler waveform. Being aware of this prevents falsely reassuring a diabetic patient with a limb-threatening problem.

• Fontaine: I asymptomatic, II claudication, III rest pain, IV tissue loss; critical limb ischaemia = rest pain >2 weeks/ulcer/gangrene.
• ABPI: normal ~1.0, <0.9 = PAD, <0.5 = critical; falsely high in diabetics (calcified vessels).
• Manage: stop smoking (key) + statin + antiplatelet + risk factors; exercise for claudication; revascularise (angioplasty/bypass) for critical ischaemia.

Fontaine staging tracks progression from claudication to tissue loss.

• Chronic limb ischaemia = atherosclerotic reduction in limb arterial supply; spectrum from claudication to critical limb ischaemia.
• Risk: smoking (strongest), diabetes, hypertension, hyperlipidaemia, age, male.
• Fontaine: I asymptomatic, II claudication, III rest pain (relieved hanging foot down), IV tissue loss; signs — absent pulses, cold pale limb, arterial ulcers, positive Buerger's test.
• ABPI <0.9 = PAD, <0.5 = critical (falsely high in diabetes); duplex/CT-MR angiography for mapping.
• Stop smoking + statin + antiplatelet + risk-factor control; exercise for claudication; revascularise (angioplasty/bypass) for critical ischaemia; amputation if unsalvageable.