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

In a patient with diabetes, hypertension, and known PAD presenting with sudden onset leg pain, paresthesia, and diminished pulse—classic signs of acute limb ischemia—CT angiography should be performed immediately as the initial diagnostic test. 1, 2

Why CTA is the Correct Choice

• The American College of Radiology explicitly recommends CTA as the preferred initial imaging modality for acute limb ischemia, rating it 7-8 out of 10, because it rapidly reveals both the exact level of arterial occlusion and the underlying atherosclerotic disease necessary for immediate revascularization planning 1, 2

• CTA evaluates the entire lower extremity arterial circulation in a single study, including aortoiliac, femoral-popliteal, and tibial-pedal vessels, providing comprehensive anatomic detail that is critical when "time is tissue" 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 1

• 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 <0.9 is useful for detecting chronic PAD in asymptomatic patients 3, this patient's acute presentation with the "6 Ps" (pain, paresthesia, pulselessness, pallor, poikilothermia, and potential paralysis) demands immediate anatomic imaging 1, 2

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

• Ultrasound is particularly limited by heavy calcification (common in diabetic patients), poor vessel accessibility, and inability to evaluate multilevel disease 1

Critical Management Principles

• 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 (Rutherford Class IIb) or paralysis (Class III) is present, as skeletal muscle tolerates ischemia for only 4-6 hours before permanent damage occurs 1, 2

• The principle of "time is tissue" applies: delays beyond 4-6 hours dramatically increase the risk of amputation and death 1

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

• The combination of diabetes, hypertension, and known PAD places this patient at extremely high cardiovascular risk, making prompt revascularization even more critical 1

• Triphasic pedal Doppler waveforms would help exclude PAD in chronic settings 3, but this patient's acute presentation with diminished pulse already indicates arterial compromise requiring anatomic imaging