Chronic Limb Ischaemia

Introduction

Chronic limb ischaemia is a form of peripheral arterial disease that results in a symptomatic reduced blood supply to the limbs.

It is typically caused by atherosclerosis (rarely vasculitis) and will commonly affect the lower limbs (however the upper limbs and gluteals can also be affected).

Around 15-20% individuals over 70yrs have peripheral arterial disease, although the majority are asymptomatic. The Framingham study demonstrated an increase in the prevalence of the disease from 0.4 per 1000 males aged 35-45yrs to 6 per 1000 males aged >65yrs.

In this article, we shall look at the clinical features, investigations and management of chronic limb ischaemia.

Risk Factors

The main risk factors for chronic limb ischaemia are smoking, diabetes mellitus, hypertension, hyperlipidaemia, increasing age, a strong family history, and obesity or physical inactivity

Clinical Features

The clinical features of chronic limb ischaemia depend on its severity (Table 1)

One of the earlier symptoms is intermittent claudication, a cramping-type pain in the calf, thigh, or buttock after walking a fixed distance (the ‘claudication distance’), that is relieved by rest within minutes. As the disease progresses, the pain becomes constant, even at rest, termed Critical Limb Threatening Ischaemia.

Table 1 – Fontaine classification of chronic leg ischaemia

On examination, affected limbs will often be colder than unaffected limbs. There may be evidence of arterial ulcers present, especially in advanced cases, and patients will typically have reduced or absent peripheral pulses. A femoral bruit may be present in advanced cases

Buerger’s test involves lying the patient supine and raising their legs until they go pale and then lowering them until the colour returns (or even becoming hyperaemic). The angle at which limb goes pale is termed Buerger’s angle; an angle of less than 20 degrees indicates severe ischaemia.

Critical Limb Threatening Ischaemia

Critical Limb Threatening Ischaemia is the advanced form of chronic limb ischaemia.

It can be clinically defined in three ways:

• Ischaemic rest pain for greater than 2 weeks duration, requiring opiate analgesia
• Presence of ischaemic lesions or gangrene objectively attributable to the arterial occlusive disease (Fig. 1)
• ABPI less than 0.5

On examination, the limbs may be pale and cold, with weak or absent pulses. Other signs include limb hair loss, skin changes (atrophic skin, ulceration, or gangrene), and thickened nails.

By James Heilman, MD (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Figure 1 – Gangrene as a result of peripheral vascular disease, indicating critical limb threatening ischaemia

Differential Diagnoses

There are two major differential diagnoses* for a patient presenting with limb ischaemia symptoms:

• Spinal stenosis (‘neurogenic claudication’)
  • Typically have pain from the back radiating down the lateral aspect of the leg (tensor fascia lata), often have symptoms on initial movement or symptoms that are relieved by sitting rather than standing
• Acute limb ischaemia
  • Clinical features that are less than 14 days duration, often presenting within hours.

Other rare causes of non-atherosclerotic lower limb ischaemia include popliteal artery entrapment syndrome, persistent sciatic artery, iliac endofibrosis, cystic adventitial disease, or Buerger’s disease.

*Acute-on-chronic ischaemia is a more complex condition whereby there is an acute often embolic event in a patient with previous peripheral arterial disease. These patients are sub-classified as they typically have a longer duration in which the limb is salvageable.

Investigations

The diagnosis of chronic limb ischaemia is clinical. The ankle-brachial pressure index (ABPI) is used to confirm the diagnosis and quantify severity of chronic limb ischaemia (Table 2); important to remember that any ABPI value >1.2 should be interpreted with caution, as calcification and hardening of the arteries may cause a falsely high ABPI.

Table 2 – Severity and ABPI measurement

Any critical limb threatening ischaemi (in the presence of a femoral pulse) should have initial radiological assessment with a Doppler ultrasound, used to assess the severity and anatomical location of any occlusion should be undertaken. Further imaging can be achieved via CT angiography (CTA) or MR angiography (MRA).

Due to concurrent cardiovascular risk factors seen in patients with chronic limb threatening ischaemia, patients should also have a cardiovascular risk assessment. This includes blood pressure, blood glucose, lipid profile and ECG.

In addition, any patient presenting with chronic limb threatening ischaemia <50yrs without significant risk factors should also have a thrombophilia screen and homocysteine levels* checked.

*A lower homocysteine level has been associated with reduced risk of cardiovascular events

Management

Medical Management

Most patients with chronic limb ischaemia require cardiovascular risk factor modification:

• Lifestyle advice (smoking cessation, regular exercise, weight reduction)
• Statin therapy (ideally atorvastatin 80mg OD)
• Anti-platelet therapy (ideally clopidogrel 75mg OD)
• Optimise diabetes control

Enrollment into a local supervised exercise programme has been shown to improve walking distance and claudication distance, and should be used as first line therapy in any patient without critical limb ischaemia

The course of chronic limb ischaemia is variable and most patients’ symptoms do improve on lifestyle changes and medical management alone. It is important to encourage patients to walk through the pain to encourage the development of new blood vessels and establishment of a collateral circulation.

Surgical Management

Current guidance states that surgical intervention can be offered in suitable patients if (i) risk factor modification has been discussed; and (ii) supervised exercise has failed to improve symptoms.

Any patients with critical limb ischaemia should be urgently referred for surgical intervention. Patients who are an inpatient should be treated within 5 days; if they are stable, and suitable for an outpatient pathway, they should be treated within 2 weeks.

There are two main surgical options available:

• Angioplasty with or without stenting (Fig. 2)
• Bypass grafting, typically used for diffuse disease or in younger patients

A combination, such as initial surgery to clean a specific lesion allowing access for angioplasty to another region, can often be trialled. Amputations are considered for any patients who are unsuitable for revascularisation with ischaemia causing incurable symptoms or gangrene leading to sepsis.

By TeachMeSeries Ltd (2024)

Figure 2 – Schematic demonstrating angioplasty and stenting for patients with limb ischaemia

Complications

Chronic limb ischaemia can result in sepsis (secondary to infected gangrene), acute-on-chronic ischaemia, amputation, and reduced mobility and quality of life.

Over a 5 year period, of those patients with intermittent claudication:

• Most will have stable claudication or improve
• 10-20% develop worsening symptoms
• 5-10% develop critical limb ischaemia

Two years following a below-knee amputation for chronic limb ischaemia, 15% require a further above knee amputation, 30% have died, and only 40% have full mobility.

The 5 year mortality rate in those diagnosed with chronic limb ischaemia is around 50%. Amputation is eventually required in 1-2% of all cases (increases to 5% in people with diabetes mellitus)