How should I differentiate between acute limb ischaemia and other causes of limb pain in a primary care setting?

To differentiate acute limb ischaemia (ALI) from other causes of limb pain in primary care, focus on the sudden onset of symptoms and the classical clinical features known as the '6 Ps': pain, pallor, pulselessness, paresthesia, paralysis, and poikilothermia (coldness). Acute limb ischaemia typically presents with severe, sudden limb pain accompanied by absent or diminished pulses distal to the affected area, pale or mottled skin, sensory loss, motor weakness, and a cold limb. These signs indicate an urgent vascular emergency requiring immediate referral to a vascular specialist.

In contrast, other causes of limb pain such as musculoskeletal injury, neuropathy, or chronic peripheral arterial disease usually have a more gradual onset, less severe pain, and preserved pulses. Examination should include palpation of femoral, popliteal, and foot pulses and assessment for signs of critical limb ischaemia such as ulceration or gangrene.

Measurement of the ankle brachial pressure index (ABPI) can aid diagnosis but may be less reliable in acute settings or in patients with diabetes. Immediate referral is warranted if ALI is suspected due to the risk of limb loss.

This approach aligns with NICE guidance on peripheral arterial disease diagnosis and management emphasizing clinical assessment of symptoms and pulses to identify critical limb ischaemia and the need for urgent specialist input.