What is the most appropriate initial diagnostic study for a woman with progressive right leg pain, a cool right lower extremity, and ulcerated lesions on several toes and the lateral malleolus?

Ankle-Brachial Index (ABI) is the Most Appropriate Initial Diagnostic Study for Peripheral Arterial Disease

The ankle-brachial index (ABI) should be the first diagnostic test performed for this patient with progressive right leg pain, cool right lower extremity, and ulcerated lesions on the toes and lateral malleolus, as these findings strongly suggest peripheral arterial disease (PAD). 1

Clinical Presentation Analysis

The patient's presentation shows classic signs of peripheral arterial disease:

• Progressive right leg pain
• Cool right lower extremity (decreased temperature)
• Ulcerated lesions on several toes and lateral malleolus

These findings represent a concerning clinical picture that requires prompt evaluation for limb-threatening ischemia.

Diagnostic Algorithm

Step 1: Initial Diagnostic Test - ABI

• The ABI is the recommended initial diagnostic test for suspected PAD 1
• It is simple, non-invasive, and inexpensive
• Normal ABI range: 0.9-1.4 2
• An ABI <0.9 confirms the diagnosis of PAD 1
• An ABI <0.6 indicates significant ischemia with respect to wound healing potential 1

Step 2: If ABI >1.4 or Non-Compressible Vessels

• Proceed to toe-brachial index (TBI) 1, 2
• This is particularly important in patients with diabetes or chronic kidney disease who may have calcified vessels 1
• A TBI <0.7 strongly suggests PAD 1

Step 3: Based on ABI/TBI Results

• If ABI <0.6 or toe pressure <30 mmHg: Severe ischemia requiring urgent vascular evaluation 1
• If ABI 0.6-0.9 or toe pressure 30-55 mmHg: Moderate ischemia requiring further assessment 1

Evidence Strength and Rationale

The ABI is strongly recommended by multiple guidelines:

• The American College of Cardiology/American Heart Association guidelines recommend ABI as the initial test to confirm the diagnosis of PAD 1
• The ABI has high specificity (83.3-99.0%) for detecting significant stenosis 3
• While sensitivity can vary (15-79%), especially in elderly and diabetic patients 3, it remains the most appropriate initial test due to its non-invasive nature and widespread availability

Important Considerations

• The presence of ulcerated lesions on the toes and lateral malleolus in combination with a cool extremity strongly suggests PAD rather than venous disease 4, 5
• Only 2.1% of leg ulcers are due to uncommon etiologies unrelated to arterial or venous pathology 5
• The ABI should be performed with the patient in a supine position using a Doppler device to measure systolic pressures at the ankles and arms 1
• If the ABI is abnormal, comprehensive vascular imaging will be necessary to evaluate revascularization options 1

Pitfalls to Avoid

1. Delay in diagnosis: Do not delay ABI measurement in a patient with signs of limb ischemia, as early diagnosis is crucial for limb salvage
2. Misinterpreting falsely elevated ABI: In patients with diabetes or renal disease, vessels may be non-compressible, resulting in falsely elevated ABI values (>1.4) 1
3. Relying solely on pulse examination: Palpable pulses do not exclude PAD; objective testing with ABI is necessary 1
4. Attributing ulcers to "small vessel disease" without proper vascular assessment: This common error can lead to delayed appropriate treatment 2

The ABI is a critical first step in the diagnostic pathway for this patient with suspected PAD, providing objective evidence to guide further management decisions and potentially prevent limb loss.