In a patient with diabetes mellitus, hypertension, and peripheral arterial disease presenting to the emergency department with sudden leg pain, paresthesia, and diminished pulses, what is the most appropriate initial investigation?

CT Angiography is the Most Appropriate Initial Investigation

In a patient presenting with sudden onset leg pain, paresthesia, and diminished pulses—the classic signs of acute limb ischemia—CT angiography (CTA) should be performed immediately as the initial investigation. This is a vascular emergency requiring rapid anatomic diagnosis to plan urgent revascularization and prevent limb loss. 1, 2, 3

Why CT Angiography is the Correct Answer

Acute Limb Ischemia Requires Immediate Anatomic Imaging

• The sudden onset of symptoms distinguishes this as acute limb ischemia, not chronic PAD, which demands emergent vascular diagnostic testing to establish the ischemic cause and guide immediate revascularization. 4

• The ACC/AHA guidelines explicitly state that sudden onset ischemic leg symptoms with signs of acute limb ischemia (the five "Ps": pain, pulselessness, pallor, paresthesias, and paralysis) should lead to emergent vascular diagnostic testing. 4

• CTA provides rapid, comprehensive anatomic detail of the entire lower extremity arterial circulation—including the level of occlusion, degree of atherosclerotic disease, and below-knee vessel patency—all critical information needed for immediate revascularization planning. 1, 2, 3

CTA is Guideline-Recommended for Acute Presentations

• The American College of Radiology rates CTA as the preferred initial imaging modality (rating 7-8) for acute limb ischemia because it is fast and reveals both the thrombosis and underlying atherosclerotic plaque to plan an appropriate treatment strategy. 1, 2, 3

• CTA evaluates the entire arterial tree including aortoiliac, femoral-popliteal, and tibial-pedal vessels in a single study, allowing immediate diagnosis and treatment planning while being widely available in emergency settings. 1, 2, 3

• The principle of "time is tissue" applies—delays beyond 4-6 hours increase amputation risk, making rapid anatomic imaging essential. 1, 2

Why ABI is Incorrect

ABI is for Screening Chronic Disease, Not Acute Emergencies

• The ACC/AHA guidelines state that ABI is indicated for screening and diagnosis of chronic lower extremity arterial disease, not for acute presentations requiring urgent revascularization. 1, 2

• ABI only confirms arterial occlusion but provides no information about the location, cause, or anatomic details needed for treatment planning in acute limb ischemia. 1, 2, 3

• While ABI is useful for establishing PAD diagnosis in stable patients with claudication or asymptomatic disease, this patient's sudden onset symptoms with diminished pulses indicate acute arterial occlusion requiring immediate anatomic imaging, not a screening test. 4

ABI Can Be Falsely Elevated in Diabetics

• In diabetic patients, ABI >1.3 indicates non-compressible vessels due to medial arterial calcification, rendering the test unreliable for assessing perfusion severity. 4, 1

• This patient's diabetes and PAD history make medial calcification likely, further limiting ABI utility in the acute setting. 4

Why Doppler Ultrasound is Incorrect

Doppler is Too Limited for Acute Limb Ischemia

• Duplex ultrasound is too time-consuming, operator-dependent, and limited in scope for acute limb ischemia evaluation in the emergency setting. 1, 2, 3

• The ACC/AHA guidelines state that duplex ultrasonography should generally be reserved for use in symptomatic patients in whom anatomic diagnostic data are required for care, but it cannot provide the comprehensive anatomic mapping of the entire arterial tree needed for urgent revascularization planning. 4

• Doppler is limited by operator expertise requirements, poor accessibility of deep vessels, heavy calcification (common in diabetics), and poor overall accuracy if multilevel disease is present. 1, 2

Critical Management Principles

Immediate Actions While Obtaining CTA

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

• Obtain vascular surgery consultation emergently—do not delay for imaging if Rutherford Class IIb (motor weakness) or III (paralysis) is present, as some patients should proceed directly to surgical thromboembolectomy. 1, 2

Revascularization Planning

• The potential for limb salvage, duration of ischemia, and arterial anatomy are critical factors in determining the method of revascularization (endovascular vs. surgical). 4

• An endovascular-first approach is preferred for most patients, with similar 1-year outcomes to open surgery. 1, 2

Common Pitfalls to Avoid

• Do not order ABI as the primary investigation in acute limb ischemia—it wastes precious time and provides no actionable anatomic information for revascularization. 1, 2, 3

• Do not delay CTA for concerns about contrast nephropathy in this patient's CKD—the benefit of rapid diagnosis and limb salvage outweighs the risk of worsening kidney function in this emergency. 1, 2

• Do not dismiss rest pain as neuropathy in diabetic patients—the presence of sudden onset pain with diminished pulses demands arterial evaluation regardless of neuropathy history. 4, 1

• Do not delay treatment for echocardiography—while useful later to identify embolic sources (e.g., atrial fibrillation), it is not part of the acute workup and should not delay revascularization. 1, 2