The Role of Blood Flow in Diabetic Foot Ulcers

For a long time, many in the medical field have believed that diabetic foot ulcers (DFUs) are caused mainly by nerve damage, with blood flow playing only a minor role. But it’s time to rethink this idea. DFUs exist on a spectrum, ranging from those caused purely by nerve damage to those caused by severe blood flow problems. Recognizing this range is essential for accurate diagnosis, effective treatment, and, most importantly, saving limbs.

The Spectrum of Diabetic Foot Ulcers

DFUs can be categorized into three main types:

1. Neuropathic DFUs: Caused primarily by nerve damage.
2. Neuroischemic DFUs: A combination of nerve damage and reduced blood flow.
3. Ischemic DFUs: Primarily caused by inadequate blood flow.

Neuropathic DFUs: The Tip of the Iceberg

Neuropathic DFUs are common and often the first type of DFU that comes to mind for many healthcare providers. These ulcers occur due to loss of sensation in the feet, leading to unnoticed injuries and pressure points. While neuropathy is a significant factor, it’s crucial to recognize that neuropathy can affect vascular function through impaired blood flow regulation, and concurrent vascular issues cannot be ruled out. Therefore, even in seemingly “pure” neuropathic DFUs, a vascular assessment is essential to ensure optimal healing conditions.

Neuroischemic DFUs: The Hidden Danger

Neuroischemic diabetic foot ulcers (DFUs) make up a large portion of all DFUs, yet they often go undiagnosed. These ulcers result from nerve damage and reduced blood flow, creating a unique diagnostic challenge. Neuropathy can mask key symptoms of poor circulation, like claudication or rest pain, making it harder to identify vascular issues. Additionally, these ulcers often exhibit features of both neuropathic and ischemic wounds, further complicating their assessment. Recognizing and addressing this overlap is crucial for effective treatment. Assuming a DFU is purely neuropathic without a proper vascular assessment can lead to inadequate treatment and poor outcomes.

Ischemic DFUs: When Blood Flow is the Primary Culprit

At the far end of the spectrum are ischemic DFUs, primarily caused by inadequate blood flow to the foot. These ulcers:

• Often have a pale or bluish appearance
• May be painful (if neuropathy isn’t severe)
• Typically occurs on the toes, foot margins, or heel.

Ischemic DFUs are particularly challenging to heal without addressing the underlying vascular issues.

The Challenge of Vascular Assessment

When evaluating a patient with a lower extremity wound, particularly a DFU, one of the most critical steps is to exclude ischemia as a potential contributor and determine if revascularization is required. However, this process is complex and nuanced.

Limitations of Clinical Examination

While a thorough clinical examination, including identifying risk factors and physical examination findings, is crucial, it’s important to understand its limitations:

• Clinical examination helps identify patients who likely have Peripheral Arterial Disease (PAD) – in other words, to “rule in” PAD.
• However, clinical examination alone is not reliable for ruling out significant PAD. It has a poor negative predictive value and should not be used in isolation to triage patients with non-healing ulcers.
• Surprisingly, patients with palpable pulses may still have significant PAD contributing to their ulcer.

The Complexity of Objective Testing

Given the limitations of clinical examination, objective testing is essential. However, all currently available physiologic evaluation modalities have difficulties and limitations:

1. Ankle-Brachial Index (ABI): Often considered the gold standard for detecting PAD, the ABI has limited negative predictive value in the setting of Chronic Limb-Threatening Ischemia (CLTI). It can be falsely reassuring or negative in 30-40% of patients, particularly those with medial artery calcification (MAC).
2. Toe-Brachial Index (TBI) and Toe Systolic Pressures (TSP): Measuring blood flow at the toe level is crucial for improving the detection of significant ischemia. However, TBIs should be considered screening tests, while TSPs are diagnostic tests.
3. Skin Perfusion Pressure (SPP): While an option for vascular testing in patients with CLTI, SPP is not as well validated and is essentially no longer used.
4. Pedal Artery Acceleration Time (PAT): This emerging technique uses Doppler ultrasound to measure blood flow acceleration in the pedal arteries. While promising, particularly for patients with MAC, it’s a newer modality that requires further validation.

Best Practices for Vascular Assessment

Given these challenges, a comprehensive approach to vascular assessment is crucial:

1. Start with a detailed history and physical examination.
2. Follow up with objective testing, typically beginning with TBI/TSP.
3. Recognize that foot ulcers occur on a spectrum from neuropathic to neuro-ischemic to ischemic.
4. Be aware that diagnosing PAD is not always straightforward and may require multiple testing modalities.
5. Before any amputation, referral to a critical limb expert for catheter angiography should be mandatory.

The Promise of Pedal Artery Acceleration Time

While all current testing methods have limitations, the Pedal Artery Acceleration Time (PAT) test is emerging as a promising new approach to vascular assessment in patients with DFUs. Here’s why PAT is gaining attention:

1. Non-invasive and Pain-free: Unlike some traditional methods, PAT is completely non-invasive, making it comfortable for patients.
2. Highly Accurate: PAT provides a more precise measurement of blood flow in the foot, even in patients with arterial calcification where other tests might be less reliable.
3. Quick and Efficient: The test can be performed quickly, providing immediate results to guide treatment decisions.
4. Detects Subtle Changes: PAT can identify mild to moderate arterial disease that might be missed by other tests, allowing for earlier intervention.
5. Quantifiable Results: PAT provides objective, numerical data that can be used to track changes in blood flow over time.
6. Guides Treatment: The results of a PAT test can help determine whether a patient needs further vascular intervention, such as angioplasty or bypass surgery.

The Importance of Early Detection

At Vascular and Interventional Experts (VIE), we’ve found that the PAT test is particularly valuable for patients with diabetes, as it can detect vascular issues early, even before symptoms become apparent. This early detection is crucial for preventing the progression of DFUs and potentially saving limbs.

Accurate vascular assessment is critical in managing diabetic foot ulcers, as not all DFUs or vascular issues are alike. At VIE, we’re committed to providing thorough, expert evaluations to ensure no patient misses out on potentially limb-saving treatments due to inadequate vascular assessment. We specialize in thorough evaluations to ensure patients receive limb-saving care. Recognizing the spectrum of DFUs—neuropathic, neuroischemic, and ischemic—is critical. Advanced tools like the PAT test help us deliver precise diagnoses and effective treatments. Patients should advocate for comprehensive vascular assessments, and healthcare providers must consider vascular health a vital part of DFU care.  If you have a diabetic foot ulcer, contact us to benefit from our comprehensive and expert care.