ALI can be as a result of thrombosis, embolism or trauma.2
Thrombosis (80-85%) is most commonly due to plaque rupture in an atherosclerotic segment (thrombosis-in-situ) in patients with peripheral arterial disease (PAD).
A thrombus may also form in the context of:
Embolism (10-15%) mainly arises from a thrombus in the left atrium (in association with atrial fibrillation) or a mural thrombus (following a myocardial infarction).
Other sources include:
Prostheses (heart valves or bypass grafts)
Aneurysms (especially popliteal and abdominal aortic aneurysms)
Trauma (including iatrogenic, 5%) can be as a result of iatrogenic injury during interventional procedures, such as percutaneous coronary intervention. These have increased prevalence over the last two decades.
The risk factors for ALI are similar to the risk factors for peripheral arterial disease (PAD):1
However, not all patients with ALI will have the presence of risk factors.
The classical features of ALI are summarised as the six P’s (developing over a period of less than 2 weeks):1
The six P’s of acute limb ischaemia
Perishingly cold (poikilothermia)
Typical symptoms of ALI include:
Pain in the affected limb usually present at rest
Altered sensation (paresthesia)
Paralysis in the affected limb (this is a late sign)
Other important areas to cover in the history include:
Past medical history: if an embolic cause is suspected, a detailed history should explore potential sources (e.g. atrial fibrillation, recent myocardial infarction).
Predisposing risk factors: ask about conditions predisposing to peripheral arterial disease (PAD), especially diabetes mellitus (a major risk factor), hypertension and hypercholesterolaemia.
Medication history: if the patient has established PAD, ask about medications (e.g. antiplatelets), and whether they are compliant with them.
Social history: it is important to establish the patient’s smoking habits, as smoking is the single biggest risk factor associated with PAD.1
In the context of suspected ALI, a thorough peripheral vascular examination is necessary. See the Geeky Medics guide here for more information.
The clinical presentation of ALI can vary greatly but the most common findings are:1
Marble white appearance of the skin
Absent limb pulses on palpation
Less common findings, which usually appear in later stages, include:1
Paraesthesia (with reduced or complete loss of light touch sensation in the distal limb)
Paralysis (with the inability to wiggle toes or move fingers)
When assessing for limb ischaemia, a normal contralateral limb with palpable pulses is a sensitive sign for embolic occlusion in the abnormal limb.1
Embolic vs thrombotic acute limb ischaemia
It is important to try and distinguish embolic from thrombotic ALI.
As opposed to thrombotic ALI, the sudden nature of embolic ALI does not provide the body with sufficient time to build up compensatory collaterals. This makes urgent intervention in embolic ALI a necessity if the limb is to be salvaged.1,2,3
This table summarises the key differences between thrombotic and embolic ALI:
Peripheral arterial disease
History of PAD symptoms
Previous vascular surgery or endovascular interventions
History of AF, recent MI
Appearance and feel
Less cold, cyanotic
Palpation of artery
Contralateral leg pulses
The Rutherford classification
In addition, the Rutherford classification for grading the severity of ALI is useful in determining limb viability. The Rutherford classification highlights the variability in the presentation of ALI.2
Limb viable, not immediately threatened
Limb marginally threatened, salvageable if promptly treated
Limb immediately threatened, salvageable with immediate revascularisation
More than toes, pain at rest
Mild or moderate
Limb irreversibly damaged, major tissue loss or permanent nerve damage inevitable
The main differential diagnosis to consider is critical limb ischaemia (CLI). It is important to differentiate between ALI and CLI due to differences in urgency and management.
CLI is caused by chronic arterial occlusion due to peripheral arterial disease with symptoms lasting longer than 2 weeks. It is characterised by rest pain, non-healing ulcers and gangrene.1,2
Acute limb ischaemia
Critical limb ischaemia
≤ 2 weeks
≥ 2 weeks
Sudden, at rest, calf tenderness
Gradual, at rest
Pale, “marble white”
Other diagnoses to consider include:1,2
Acute deep vein thrombosis
Thromboangiitis obliterans (Buerger disease)
Duplex ultrasound/Doppler scan: to confirm the absence of pulses.