What is the most appropriate initial investigation for a 60-year-old patient with a history of Diabetes Mellitus (DM) and Hypertension (HTN) who is asymptomatic but has a family history of Peripheral Artery Disease (PAD)?

Ankle-Brachial Index (ABI) is the Most Appropriate Initial Investigation

For this 60-year-old asymptomatic patient with diabetes and hypertension concerned about PAD due to family history, the ankle-brachial index (ABI) is the recommended first-line diagnostic test. 1

Rationale for ABI as Initial Test

Guideline-Based Recommendations

• The 2016 AHA/ACC guidelines explicitly recommend resting ABI for patients ≥65 years of age, or ≥50 years with risk factors including diabetes mellitus and hypertension 1

• This patient meets multiple criteria for ABI testing: age 60 with both diabetes and hypertension, placing him in the high-risk category even without symptoms 1

• The ABI should be measured in both legs to establish baseline values and confirm diagnosis, with results reported as: abnormal (≤0.90), borderline (0.91-0.99), normal (1.00-1.40), or noncompressible (>1.40) 1

Why Not the Other Options

• CT and CT angiography are NOT appropriate for asymptomatic patients - the 2016 AHA/ACC guidelines give a Class III (Harm) recommendation against invasive and noninvasive angiography (including CTA) for anatomic assessment of asymptomatic PAD 1

• Doppler ultrasound (duplex) is reserved for symptomatic patients in whom revascularization is being considered, not for initial screening of asymptomatic individuals 1

• Anatomic imaging studies (CT angiography, duplex ultrasound) are generally reserved for highly symptomatic patients being considered for revascularization and may confer procedural risk 1

Clinical Context and Epidemiology

• Approximately 21-23% of patients older than 55-65 years have PAD, with more than 40% being asymptomatic 1

• Patients with diabetes, hypertension, and family history have synergistically increased risk for PAD and critical limb ischemia 2

• The ABI test demonstrates high specificity (83.3-99.0%) for detecting ≥50% stenosis, though sensitivity varies (15-79%), particularly in elderly and diabetic patients 3

Important Caveats for This Patient

Diabetes-Related Considerations

• In diabetic patients, ABI may be falsely elevated (>1.40) due to arterial calcification from medial wall sclerosis (Mönckeberg sclerosis) 2, 4

• If the ABI is >1.40 (noncompressible vessels) or between 0.91-1.40 but clinical suspicion remains high, proceed to toe-brachial index (TBI) measurement 1

• The TBI should be used when ABI is unreliable due to noncompressible vessels, which commonly occurs in patients with long-standing diabetes 1

Follow-Up Algorithm

• If ABI is abnormal (≤0.90): PAD is confirmed - initiate aggressive cardiovascular risk reduction including smoking cessation, statin therapy, antiplatelet agents, and blood pressure control 2, 4

• If ABI is borderline (0.91-0.99): Consider exercise ABI testing if symptoms develop or clinical suspicion increases 1

• If ABI is >1.40: Measure TBI immediately as this indicates noncompressible vessels and the ABI result is unreliable 1

Prognostic Importance

• Early detection of PAD is crucial as it classifies patients as "very high cardiovascular risk," requiring aggressive risk factor modification 2

• Patients with PAD are at increased risk for cardiovascular death and all-cause mortality, making identification important even in asymptomatic individuals 1

• The presence of PAD in diabetic patients indicates increased risk for other cardiovascular diseases, necessitating comprehensive cardiovascular risk assessment 2

Answer: B - ABI (Ankle-Brachial Index)