In a patient with diabetes mellitus (DM), hypertension (HTN) and peripheral arterial disease (PAD) presenting with sudden leg pain, paresthesia and a diminished pulse, what is the most appropriate initial investigation: CT angiography, ankle‑brachial index (ABI), or Doppler ultrasound?

Most Appropriate Initial Investigation for Acute Limb Ischemia

CT angiography is the most appropriate initial investigation for this patient presenting with sudden onset leg pain, paresthesia, and diminished pulse. 1, 2, 3

Why CT Angiography is the Correct Answer

CT angiography provides rapid, comprehensive anatomic detail of the entire lower extremity arterial circulation in a single study, which is essential for immediate revascularization planning in this emergency. 1, 2, 3 The American College of Radiology explicitly rates CTA as the preferred initial imaging modality (rating 7-8 out of 10) because it rapidly reveals both the exact level of arterial occlusion and the underlying atherosclerotic disease necessary for treatment planning. 3

Key Advantages of CTA in This Clinical Scenario

• CTA evaluates the entire arterial tree including aortoiliac, femoral-popliteal, and tibial-pedal vessels, providing the anatomic roadmap needed for urgent revascularization. 1, 2, 3

• Time is tissue: The sudden onset of symptoms distinguishes this as acute limb ischemia (ALI), not chronic PAD, requiring urgent anatomic imaging within hours to prevent permanent tissue damage and limb loss. 1, 3

• CTA identifies both the occlusion site and underlying atherosclerotic disease, allowing simultaneous assessment of acute thrombosis superimposed on chronic PAD—critical information in this patient with known PAD. 1, 3

• Widely available in emergency settings and can be performed rapidly (typically 10-15 minutes), which is crucial when skeletal muscle tolerates ischemia for only 4-6 hours before permanent damage occurs. 1, 3

Why ABI is Incorrect

The American College of Cardiology explicitly states that ABI is indicated for screening and diagnosis of chronic lower extremity arterial disease, NOT for acute presentations requiring urgent revascularization. 3

• ABI only confirms that arterial occlusion exists but provides no information about the location, cause, or anatomic details needed for treatment planning in acute limb ischemia. 1, 3

• ABI is a screening tool for chronic PAD, not a diagnostic test for acute emergencies—this patient already has known PAD, making screening redundant. 4, 3

• In diabetic patients, ABI has limited performance due to medial arterial calcification causing falsely elevated or non-compressible readings (ABI >1.40), which is common in this population. 4, 5

Why Doppler Ultrasound is Incorrect

Doppler ultrasound is too time-consuming, operator-dependent, and limited in scope for acute limb ischemia evaluation in the emergency setting. 1, 3

• Cannot provide comprehensive anatomic mapping of the entire arterial tree needed for revascularization planning in this emergency. 3

• The American College of Radiology notes that duplex ultrasound is limited by the need for operator expertise, poor accessibility of vessels, heavy calcification (common in diabetics), and poor overall accuracy if multilevel disease is present. 1

• Duplex ultrasound is indicated as first-line imaging for chronic stable PAD, not for acute presentations where rapid comprehensive assessment is mandatory. 4

Critical Management Principles

Immediate Actions While Awaiting CTA

• Start intravenous unfractionated heparin immediately to prevent thrombus propagation while awaiting imaging. 1, 2, 3

• Obtain vascular surgery consultation emergently—do not delay for imaging if motor weakness or paralysis is present, as this indicates Rutherford Class IIb or III requiring intervention within 6 hours. 1, 3

Special Considerations in This Patient

• Despite concerns about contrast-induced nephropathy in patients with diabetes and hypertension, the benefit of rapid diagnosis and limb salvage outweighs the risk of worsening kidney function in this emergency. 1, 3

• The combination of diabetes, hypertension, and known PAD places this patient at extremely high cardiovascular risk, making prompt revascularization even more critical. 3

• Assess the "6 Ps" while preparing for CTA: Pain, Pallor, Pulselessness, Poikilothermia (cold limb), Paresthesias, and Paralysis to determine Rutherford classification and urgency. 2

Common Pitfalls to Avoid

• Do not waste time obtaining ABI or Doppler when clinical presentation clearly indicates acute limb ischemia—proceed directly to CTA. 3

• Do not delay CTA for echocardiography to assess for embolic source—this can be done after limb salvage is secured. 1

• If profound sensory loss and paralysis are present (Rutherford Class III), proceed directly to surgery without delay for imaging, as revascularization must occur within 4-6 hours. 2