How to assess for atherosclerosis of the lower extremities
There are three types of peripheral arterial disease (PAD) in the lower extremities:
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.
What are the risk factors for atherosclerosis?
There are three key risk factors for atherosclerosis that chronically contribute to arterial wall damage:
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.
Figure 1. Risk factors for atherosclerosis include diabetes, smoking, and hypertension.
What are the symptoms of atherosclerotic PAD?
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.
Figure 2. Claudication, a symptom of atherosclerotic peripheral arterial disease, involves pain with activity that is relieved with rest.
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.
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.
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:
- Assess pedal pulses
- Inspect the feet and lower legs
- Perform an ankle-brachial index (ABI) test
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.
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.
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 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.
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.
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