What is the most appropriate initial investigation for a patient with Diabetes Mellitus (DM), Hypertension (HTN), and Peripheral Artery Disease (PAD) presenting with sudden onset leg pain, paresthesia, and a diminished pulse?

CT Angiography (CTA) is the Most Appropriate Initial Investigation

For a patient presenting with sudden onset leg pain, paresthesia, and diminished pulse—the hallmark features of acute limb ischemia—CT angiography should be performed immediately as the primary diagnostic test. 1, 2

Why CTA is the Definitive Choice

The American College of Radiology explicitly rates CTA as the preferred initial imaging modality (rating 7-8 out of 10) for acute limb ischemia because it rapidly reveals both the exact level of arterial occlusion and the underlying atherosclerotic disease necessary for immediate revascularization planning. 3, 2

CTA provides comprehensive anatomic detail of the entire lower extremity arterial circulation in a single study—including aortoiliac, femoral-popliteal, and tibial-pedal vessels—which is critical when "time is tissue" in acute limb ischemia. 1, 2 The sudden onset of symptoms distinguishes this as acute limb ischemia (ALI), not chronic PAD, which requires urgent anatomic imaging within hours to prevent permanent tissue damage and limb loss. 1

Why ABI is Inadequate in This Emergency

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, 1, 2

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, 2 While ABI measurement and handheld Doppler are simple methods to confirm arterial occlusion when the cause is not obvious 3, in this case the clinical presentation is already diagnostic—the patient needs anatomic localization for immediate revascularization, not confirmation of occlusion.

Why Doppler Ultrasound is Insufficient

Doppler ultrasound is too time-consuming, operator-dependent, and limited in scope for acute limb ischemia evaluation in the emergency setting. 1, 2 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 diabetic patients), and poor overall accuracy if multilevel disease is present. 1

Ultrasound cannot provide the comprehensive anatomic mapping of the entire arterial tree needed for revascularization planning in this emergency. 1, 2

Critical Management Principles

Immediate Actions Before Imaging

• Start intravenous unfractionated heparin immediately to prevent thrombus propagation while awaiting CTA 1, 2
• Obtain vascular surgery consultation emergently—do not delay for imaging if motor weakness or paralysis is present 1, 2

Time-Critical Nature

The principle of "time is tissue" applies: skeletal muscle tolerates ischemia for only 4-6 hours before permanent damage occurs. 1 Delays beyond this window dramatically increase the risk of amputation and death. 1, 2

Special Considerations for 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, 2 The combination of diabetes, hypertension, and known PAD places this patient at extremely high cardiovascular risk, making prompt revascularization even more critical. 2

Modern techniques such as reduced tube voltage can minimize contrast dose and reduce the risk of nephropathy. 1

Clinical Algorithm

1. Assess for the "6 Ps" of acute limb ischemia: pain, paralysis, paresthesias, pulselessness, pallor, and poikilothermia (cold extremity) 1
2. Start IV heparin immediately 1, 2
3. Order CTA of abdomen/pelvis with bilateral lower extremity runoff 3, 1, 2
4. Obtain emergent vascular surgery consultation (can be done simultaneously with imaging) 1, 2
5. Proceed to urgent revascularization (endovascular or surgical) based on CTA findings 1

Common Pitfall to Avoid

Do not waste time obtaining ABI or Doppler ultrasound as the primary investigation—these tests only confirm what is already clinically apparent (arterial occlusion) and provide no information about location, cause, or treatment planning needed in acute limb ischemia. 1, 2 The patient needs anatomic imaging for immediate revascularization planning, not screening tests designed for chronic disease evaluation. 3, 1