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 is the Most Appropriate Initial Investigation

For a patient with diabetes, hypertension, and known PAD presenting with sudden onset leg pain, paresthesia, and diminished pulse—consistent with acute limb ischemia—CT angiography (CTA) should be performed immediately as the initial diagnostic test. 1, 2, 3

Why CTA is the Definitive Choice

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

• The American College of Radiology explicitly rates CTA as "usually appropriate" for acute limb ischemia, emphasizing its ability to provide immediate diagnosis and treatment planning in a single study while being widely available in emergency settings 1, 3
• CTA allows evaluation of the entire arterial tree from aortoiliac vessels through pedal arteries, which is essential for determining the optimal revascularization approach (endovascular vs. surgical) 1, 2
• The test is fast—a crucial factor given that the principle of "time is tissue" applies, where delays beyond 4-6 hours significantly increase the risk of permanent muscle damage and limb loss 2

Why ABI is Inadequate in This Emergency

ABI is a screening tool for chronic PAD, not a diagnostic test for acute limb ischemia requiring urgent intervention. 2, 3

• 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 2, 3
• ABI only confirms the presence of arterial occlusion but provides no information about the location, cause, extent of disease, or treatment planning needed in acute limb ischemia 1, 2
• While ABI can be useful as a rapid bedside confirmation of arterial insufficiency when the diagnosis is unclear, it does not replace anatomic imaging in a patient with clear clinical signs of acute ischemia 1

Why Doppler Ultrasound Falls Short

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

• Doppler can confirm absent arterial signals but cannot provide the comprehensive anatomic mapping of the entire arterial tree needed for revascularization planning 1, 2
• The test is highly operator-dependent and has difficulty evaluating deep vessels, particularly in patients with severe calcification—common in diabetic patients with chronic kidney disease 2
• Doppler should only be considered in patients who are not suitable candidates for CTA 1

Critical Immediate Management Steps

While arranging CTA, initiate systemic anticoagulation immediately with intravenous unfractionated heparin to prevent thrombus propagation. 2, 3

• Assess the Rutherford classification by examining the "6 Ps": Pain, Pallor, Pulselessness, Poikilothermia (cold extremity), Paresthesias, and Paralysis 2, 3
• The presence of motor weakness or sensory loss beyond the toes indicates Rutherford Class IIb (immediately threatened) or Class III (irreversible), requiring urgent intervention 2
• Obtain vascular surgery consultation immediately, even before imaging is complete, as some patients with severe ischemia (profound sensory loss and paralysis) may need to proceed directly to surgical thromboembolectomy 2, 3

Special Considerations for This Patient's Comorbidities

Despite concerns about contrast-induced nephropathy in diabetic patients with potential chronic kidney disease, the benefit of rapid diagnosis and limb salvage outweighs the risk of worsening kidney function in acute limb ischemia. 2

• Modern CTA techniques with reduced tube voltage can minimize contrast dose and reduce nephropathy risk 2
• The patient's diabetes and PAD history place them at extremely high risk for major adverse cardiovascular events, all-cause mortality, and major amputation—making rapid, definitive diagnosis even more critical 2
• Atrial fibrillation should be assessed as a potential embolic source, as this changes long-term management and requires anticoagulation 2

Common Pitfalls to Avoid

• Do not delay definitive imaging to obtain an ABI first—this wastes precious time when "time is tissue" 2, 3
• Do not assume chronic PAD symptoms—the sudden onset distinguishes acute limb ischemia from chronic limb-threatening ischemia, which develops over more than 2 weeks 2
• Do not wait for laboratory results or risk stratification—proceed directly to CTA and anticoagulation based on clinical presentation 2, 3