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?

Initial Investigation for Acute Limb Ischemia

For a patient presenting with sudden onset leg pain, paresthesia, and diminished pulse—classic signs of acute limb ischemia—CT angiography (CTA) is the most appropriate initial investigation. 1, 2

Why CTA is the Correct Answer

CTA provides rapid, comprehensive anatomic detail of the entire arterial tree from the aorta to the pedal vessels, which is essential for planning urgent revascularization. 3, 1 The American College of Radiology rates CTA as "usually appropriate" for acute limb ischemia, emphasizing that it allows immediate diagnosis and treatment planning while being widely available in emergency settings. 1, 2

Key Advantages of CTA in This Clinical Scenario:

• Speed is critical: The principle of "time is tissue" applies—delays beyond 4-6 hours dramatically increase the risk of permanent damage and limb loss. 1, 2 CTA can be obtained rapidly without delaying definitive therapy. 2

• Comprehensive visualization: CTA evaluates the exact level of occlusion, degree of underlying atherosclerotic disease, and below-knee arteries—all crucial for revascularization planning. 3, 2

• Simultaneous assessment of comorbidities: In this patient with DM, HTN, and PAD, CTA can identify concurrent pathology such as aneurysmal disease or multilevel occlusions. 3

Why NOT ABI or Doppler Alone

ABI Limitations:

• ABI only confirms arterial occlusion but provides no anatomic information about the location, extent, or cause of the occlusion. 1, 2 While it establishes objective baseline measurements, it cannot guide revascularization strategy. 1

• ABI is useful as a rapid screening test and for post-treatment follow-up, but not as the definitive initial investigation in acute limb ischemia requiring urgent intervention. 2

Doppler Ultrasound Limitations:

• Duplex ultrasound is NOT recommended as the primary investigation for acute limb ischemia due to significant operator dependence, poor accessibility of deep vessels, and interference from heavy calcification (common in diabetic patients with PAD). 1

• The American College of Radiology explicitly notes these limitations make Doppler unreliable in emergency acute limb ischemia settings. 1

Clinical Algorithm for This Patient

Immediate Actions (While Arranging CTA):

1. Start systemic anticoagulation immediately with intravenous unfractionated heparin to prevent thrombus propagation. 1, 2, 4

2. Assess Rutherford classification by examining the "6 Ps": Pain, Pallor, Pulselessness, Poikilothermia (cold), Paresthesias, and Paralysis. 3, 1, 4

3. Contact vascular surgery immediately before completing imaging if any motor weakness or sensory loss beyond the toes is present—this indicates Rutherford Class IIb (immediately threatened) or Class III (irreversible) requiring emergency intervention. 1, 2

Imaging Strategy:

• Obtain CTA of the entire lower extremity including aortoiliac, femoral-popliteal, and tibial-pedal vessels. 2, 4

• If Rutherford Class III (profound sensory loss and paralysis), proceed directly to surgery without delay for imaging. 1

Special Consideration for Chronic Kidney Disease:

While this patient has DM (which may involve renal impairment), the benefit of rapid diagnosis and limb salvage outweighs the risk of contrast-induced nephropathy in acute limb ischemia. 2 Modern reduced-contrast techniques can minimize nephrotoxicity risk. 1, 2

Critical Pitfalls to Avoid

• Do not delay imaging to obtain ABI first—this wastes precious time without providing actionable anatomic information. 1, 2

• Do not rely on Doppler ultrasound as the primary diagnostic tool in acute presentations; it is too limited and operator-dependent. 1

• Do not wait for imaging if paralysis is present—this indicates irreversible ischemia requiring immediate surgical intervention. 1, 4

• Do not forget anticoagulation—start heparin immediately upon clinical suspicion, even before imaging confirmation. 2, 4

Alternative: Digital Subtraction Angiography (DSA)

For patients with severe ischemia (Rutherford Class IIb or III), proceeding directly to catheter-based DSA with intent to treat may be the most appropriate strategy, as it allows simultaneous diagnosis and endovascular intervention. 3, 1 However, CTA remains the standard initial investigation for most acute limb ischemia presentations. 1, 2