How to assess for atherosclerosis of the lower extremities

26th Feb 2021

There are three types of peripheral arterial disease (PAD) in the lower extremities:

  1. Atherosclerosis
  2. Aneurysm
  3. Trauma

First, let’s dive into atherosclerosis. Atherosclerosis involves the deposit of fatty materials that form plaque on arterial walls. This results in chronic wall damage and lumen blockage due to the plaque buildup. 

At severe stages, atherosclerosis can lead to chronic limb ischemia (CLI). Chronic limb ischemia increases the risk of infection and can eventually lead to amputation.

It is important to note that chronic limb ischemia (CLI) can refer to chronic limb ischemia, but it can also mean critical limb ischemia. Make sure to differentiate the two. Critical limb ischemia can also result from acute obstructive processes, whereas atherosclerosis (with resultant CLI) is a chronic disease. Medmastery note.

 

What are the risk factors for atherosclerosis?

There are three key risk factors for atherosclerosis that chronically contribute to arterial wall damage:

  1. Diabetes
  2. Smoking
  3. Hypertension 

Diabetes plays a large part in the development of arterial wall calcification and rigidity, which promote plaque collection. Smoking and hypertension are modifiable risk factors which also cause significant stress. Atherosclerosis is a long-term process and is commonly seen in older adults. 

Lower legs and a magnifying glass zoomed in on an arterial plaque, and a list of risk factors for atherosclerosis. Illustration.

Figure 1. Risk factors for atherosclerosis include diabetes, smoking, and hypertension.

 

What are the symptoms of atherosclerotic PAD?

Claudication

The first symptom a patient feels that indicates atherosclerotic PAD is claudication. Claudication is pain with activity that is relieved with rest. Claudication usually begins in the calf, but if the disease involves the aortoiliac system, the pain can be felt in the buttock and the thigh as well. 

that is relieved with rest. <alt text>Patient with calf pain and same patient sitting down with no pain. Illustration.

Figure 2. Claudication, a symptom of atherosclerotic peripheral arterial disease, involves pain with activity that is relieved with rest.

Rest pain

As mentioned previously, chronic and untreated atherosclerosis can evolve into advanced stages of CLI. The advanced stage typically presents with a constant, severe pain at rest which is referred to as rest pain. Rest pain usually occurs in the forefoot, heel, and toes. 

These patients are urgent surgical candidates. If left untreated, they are at risk for necrosis and amputation of the affected limb.

Typically, it is obvious when a patient is suffering from rest pain. The patient appears uncomfortable, as the pain is very severe. Often, the patient dangles their leg over the side of the bed, which helps alleviate the pain by increasing blood flow to the foot.

Patient on a hospital bed with severe leg pain, and same patient dangling the leg over the side of the bed with reduced pain. Illustration.

Figure 3. In patients suffering from rest pain due to chronic and untreated atherosclerosis, the severe pain can be reduced when the patient dangles their leg over the side of the bed. 

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How to assess a patient for atherosclerosis of the lower extremities

There are three steps to assessing a patient who presents with symptoms of lower extremity atherosclerosis: 

  1. Assess pedal pulses 
  2. Inspect the feet and lower legs
  3. Perform an ankle-brachial index (ABI) test

Hand taking a pedal pulse, lower legs and feet under a magnifying glass, Doppler pen and blood pressure cuff with a pump. Illustration.

Figure 4. The three steps to assessing a patient with symptoms of lower extremity atherosclerosis include, 1) assess pedal pulses, 2) inspect the feet and lower legs, and 3) perform an ankle-brachial index test.

Let’s get into each of these steps in more detail. 

Step 1: Assess pedal pulses 

The first step in the evaluation is to assess for pulses at the ankles. Remember that the posterior tibial artery (PTA) and dorsalis pedis artery (DPA) are the main runoff vessels. The PTA and anterior tibial artery (ATA) branch off of the distal popliteal artery, and then the ATA becomes the DPA at its distal end. 

The PTA and the DPA are routinely checked for pulse strength at the ankle level.

Lower legs showing the location of the posterior tibial artery (PTA) and dorsalis pedis artery (DPA). Illustration.

Figure 5. Pedal pulses are assessed by checking the pulse strength of the posterior tibial artery (PTA) and the dorsalis pedis artery (DPA). 

When assessing pedal pulse strength, the handheld Doppler pen is extremely helpful for hearing the volume intensity of the blood flow. It can also help you hear the blood flow sound (e.g., phasicity) which can tell you if there is a proximal disease. 

The Doppler should be readily available in most hospitals and clinics. To use the Doppler, you need gel, so don’t forget it! Medmastery note.

Diminished pedal pulses can be a sign of PAD. Sometimes these vessels naturally decrease in size as they reach the ankle and can become difficult to palpate, but the pulses aren’t technically diminished. This challenge increases when the extremity is edematous (where fluid accumulates in the extravascular tissue). Edema can interfere with palpation for a pedal pulse as well as with a Doppler pen.

Could it just be peripheral neuropathy?

It’s important to remember that diabetes is a risk factor for PAD. However, diabetes increases a patient’s risk for both PAD and peripheral neuropathy. 

Peripheral neuropathy can cause decreased sensation in the extremities, painful burning in the feet, or a pins-and-needles sensation in the feet. These symptoms are very similar to PAD symptoms. The similarity in symptoms can cause confusion and delays in the diagnosis of PAD. 

Since the symptoms of PAD and peripheral neuropathy are similar, make sure to diligently palpate the pedal pulses. If the pulses are strong, then the symptoms are not likely from PAD. 

Table summarizing how to use pedal pulse strength to distinguish between peripheral neuropathy and peripheral artery disease or edema in the lower extremities.

Table 1. Distinguishing between three potential causes of decreased sensation, burning, or pins-and-needles in the lower extremities using pedal pulse strength. 

Step 2: Inspect the feet and lower legs

As you perform the exam, you may recognize that some patients not only present with pain, but also have obvious signs of advanced disease. Ulcers and necrosis are the most severe signs of CLI and are visually obvious. Arterial ulcers usually occur over the tibia and feet. These ulcers are usually very painful.

Inspect both feet thoroughly! Peripheral neuropathy involves a loss of sensation in the extremities. Patients who have both peripheral neuropathy and peripheral artery disease (PAD) will not be able to feel the pain that is typically present with ulcers and necrosis, so it’s important to thoroughly inspect both feet. Medmastery note.

Step 3: Perform an ankle-brachial index (ABI) test

If the pedal pulses are diminished, it may be helpful to assess for arterial obstruction with an ABI test. An ABI is performed by obtaining blood pressure readings in the arms and the ankles and comparing them. 

An index for each leg is calculated from the readings. The calculation represents the amount of appropriate blood flow reaching the ankles from the heart. 

Ideally, the ratio should be one, meaning that 100% of the blood flow is reaching the ankles. If the ratio is 0.5, then 50% of the blood flow is reaching the ankles and 50% is being blocked by PAD. 

That’s it for now. If you want to improve your understanding of key concepts in medicine, and improve your clinical skills, make sure to register for a free trial account, which will give you access to free videos and downloads. We’ll help you make the right decisions for yourself and your patients.

Recommended reading

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