Podiatrists play a critical role in the identification, treatment and management of patients with peripheral arterial disease (PAD). While an estimated 8 to 12 million Americans have PAD, the disease continues to remain largely underdiagnosed.1 Symptoms of pain, aching or cramping in the legs with walking (claudication) can occur in the buttock, hip, thigh, or calf.1 However, up to 75 percent of individuals with PAD are either asymptomatic, unaware of the signs of PAD or have symptoms that are not appropriately identified by their primary healthcare provider.2-5 Those with diabetes and neuropathy may not have any of the classic symptoms and instead complain only of lower extremity fatigue that rest relieves.
With the demographic changes in Western societies trending to older, more obese people prone to type 2 diabetes and hypertension, there is increasing interest in the comorbid effects of PAD and diabetes on the cardiovascular system. The standard estimates of prevalence of lower extremity PAD based on ankle-brachial index blood pressure ratios are approximately 10 to 20 percent of community-dwelling individuals aged 65 and older and 18 to 29 percent of patients aged 50 and older in general medicine practices.6-9 Individuals with diabetes have a much higher risk for PAD with a 1 in 3 chance of developing the disease. The risk of PAD increases four times for people who smoke or have a history of smoking. Consequently, PAD within these patient populations requires early disease identification, a structured treatment plan and close patient monitoring in order to avoid complex surgical procedures, critical limb ischemia and amputation.
Unfortunately, awareness of PAD symptoms almost always occurs first with issues on the patient’s foot as the cumulative effects of diabetes and diseased arterial flow result in a cascade of events that include loss of protective sensation, toe/foot deformities, tissue breakdown, non-healing ulcers and ultimately gangrene.
Recognizing The Pros And Cons Of The Ankle Brachial Index
The most common frontline test to assess for the presence of PAD is the ankle brachial index (ABI). One obtains the ABI by measuring the systolic pressures at the brachial arteries and comparing these to the systolic pressures at the dorsalis pedis (anterior tibial) and posterior tibial arteries. For many patients, the ABI exam is a reliable and accurate PAD indicator. While the United States Preventive Services Task Force has never endorsed ABI for use as a screening tool for PAD or cardiovascular disease, all professional societies endorse the use of ABI in patients who are positive for risk indicators and signs/symptoms.10
However, the ABI is not without its limitations. Tibial artery disease occurs at a much higher rate in patients with diabetes in comparison to patients without diabetes.11 As part of the complex disease process, patients with diabetes often develop medial calcinosis in the tibial arteries, stiffening arterial walls. The significance of these less compliant or compression resistant arteries related to the ABI test is that when taking pressures at the ankle, it often requires increased cuff pressure to stop arterial flow, resulting in an artificially normal or high ABI. When comparing the compression resistant tibial artery pressures to the brachial artery pressures to calculate the index, one can find an artificially elevated ABI resulting in a misdiagnosis or underdiagnosis of the patient’s true lower extremity arterial condition.12,13 The ABI may also be falsely normal in symptomatic patients with moderate aortoiliac stenosis.11
Contraindications to ABI are documented in the Society for Vascular Ultrasound’s Lower Extremity Arterial Duplex Evaluation guidelines.11 These contraindications to ABI include: