Diabetic Ulcers Workup

Patient workup for diabetic ulcers includes blood tests, pulse-volume recording, ultrasonography, ankle-brachial index, radiography, computed tomography, magnetic resonance imaging, bone scans, and angiography.

A complete blood count should be done. Leukocytosis may signal plantar abscess or other associated infection. Wound healing is impaired by anemia. In the face of underlying arterial insufficiency, anemia may precipitate rest pain.^[15]

Assessment of serum glucose, glycohemoglobin, and creatinine levels helps to determine the adequacy of acute and chronic glycemic control and the status of renal function.

Blood testing should also include hemoglobin A1C assessment because a normal value is a surrogate marker for wound healing.^[16]

Pulse-volume recording (PVR), or plethysmography, uses pneumatic cuffs encircling the thighs, calves, ankles, feet, and, occasionally, toes to sense segmental volume changes with each pulse beat. The resulting tracings provide useful information about the hemodynamic effects of the arterial disease at each level. In severe disease, tracings at the transmetatarsal level may become nearly flat. In mild disease, particularly involving the aortoiliac segment, PVR tracings may appear normal at rest and become abnormal only after the patient walks until symptoms occur.

PVR is noninvasive and rapid and, therefore, may be repeated frequently to help assess the overall hemodynamic response to medical or surgical treatment. Ordinarily, if pedal pulses are satisfactory, arterial evaluation PVR provides no useful information.

Duplex ultrasonography can provide images of arterial segments that help localize the extent of disease, and simultaneous Doppler measurement of flow velocity can help estimate the degree of stenosis. Duplex scanning is quite useful in visualizing aneurysms, particularly of the aorta or popliteal segments. Use of this technique probably is best left to the discretion of the vascular specialist.

A handheld Doppler scanner may be used to assess arterial signals, to localize arteries to facilitate palpation of pulses, or to determine the loss of Doppler signal as a proximal blood pressure cuff is inflated (as in measurement of systolic pressure in extremity arteries).

Laser Doppler studies also have been used but may not be reliable.

The systolic pressure in the dorsalis pedis or posterior artery divided by the upper extremity systolic pressure is called the ankle-brachial index (ABI) and is an indication of severity of arterial compromise. Normal ABI averages 1.0. An ABI less than 0.9 suggests atherosclerotic disease, with a sensitivity of approximately 95%. In general, an ABI below 0.3 suggests a poor chance for healing of distal ischemic ulcerations. Unfortunately, the ABI often is falsely elevated (and thus may be unreliable) if the underlying arteries are heavily calcified, a finding common in diabetic persons.

See recommendations for the workup of patients with atherosclerotic disease of the extremities in the eMedicine article Infrainguinal Occlusive Disease.

Plain radiographic studies of the diabetic foot may demonstrate demineralization and Charcot joint and occasionally may suggest the presence of osteomyelitis. Plain radiographs are not routinely obtained in the workup of peripheral arterial occlusive disease. This is because arterial calcification seen on plain radiographs is not a specific indicator of severe atherosclerotic disease. Calcification of the arterial media is not diagnostic of atherosclerosis, and even calcification of the arterial intima, which is diagnostic of atherosclerotic disease, does not necessarily imply hemodynamically significant stenosis.

Although an experienced clinician usually can diagnose a plantar abscess by physical examination alone, computed tomography (CT) scanning or magnetic resonance imaging (MRI) is indicated if a plantar abscess is suspected but not clear on physical examination.

Bone scans are of questionable use because of a sizable percentage of false-positive and false-negative results. A recent study suggests Technetium-99m-labeled ciprofloxacin is a somewhat useful marker for osteomyelitis.^[17]

If vascular or endovascular surgical treatment is contemplated, angiography is needed to delineate the extent and significance of atherosclerotic disease. Major risks associated with conventional contrast-injection angiography are related to the puncture and to the use of contrast agents. See also Infrainguinal Occlusive Disease.

Technique

Typically, a catheter is inserted retrograde via a femoral puncture, and contrast is power-injected into the infrarenal aorta. Films are taken as the contrast is followed down to both feet. In certain cases, as with aortic occlusion, a femoral approach to the aorta may not be possible. In this case, the interventionalist (interventional cardiologist, vascular surgeon, or interventional radiologist) may use an alternative entry point, such as via the brachial or axillary artery. The arterial catheter is usually passed through a 5F sheath that is 1.6 mm in diameter. This is a sizable hole in the femoral artery, which may be only 6-10 mm in diameter. After the catheter is removed, gentle pressure must be applied to the puncture site for approximately 30 minutes. In most cases, the physician performing the angiogram may elect to use a small device to aid in closing the puncture site (“closure device”). Successful deployment of these devices eliminates the need for prolonged pressure application.

Puncture-related complications

Risks associated with catheter insertion include hemorrhage, pseudoaneurysm formation, and clotting or dislodgement of an intimal flap, which may acutely occlude the artery at or near the entry site. Use of percutaneous closure devices on the puncture sites has significantly reduced site complication rates.

Contrast-related risks

Angiographic contrast material is nephrotoxic. The risk of precipitating acute renal failure is highest in patients with underlying renal insufficiency and those with diabetes. Patients with both of these risk factors have a 30% rate of acute renal failure following contrast angiography. Hence, an acceptable serum creatinine level must be confirmed prior to elective angiography. Avoid contrast angiography (if possible) for patients with any significant degree of renal impairment. If contrast angiography is absolutely required despite renal impairment, use a minimal volume of contrast material. In addition, providing adequate hydration prior to, during, and after the procedure is essential. Oral administration of the antioxidant acetylcysteine (Mucomyst) the night prior to and then just before angiography may be protective of renal function for patients at risk of contrast-induced nephropathy.^[18]

Metformin warning

To prevent the possibility of fatal lactic acidosis, patients with diabetes who are taking metformin (Glucophage) must not take this medication immediately following contrast angiography. Patients may resume taking the medication when normal renal function is confirmed 1-2 days after contrast exposure.

Magnetic resonance angiography

Magnetic resonance angiography (MRA) is an alternative for patients who are allergic to iodinated contrast material. MRA is not innocuous. Gadolinium chelates, the contrast agents used in MRA, have been linked recently to 3 potentially serious side effects in patients with renal insufficiency: acute renal injury, pseudohypocalcemia, and nephrogenic systemic fibrosis. MRA is contraindicated in patients with implanted hardware such as a hip prostheses or pacemakers.

The resolution provided by MRA may be inadequate for the vascular surgeon in planning reconstructive procedures, particularly in the smaller infrapopliteal arteries, although MRA technology and contrast agents continue to improve.^[19]

Multidetector CT angiography

Multidetector CT (MDCT) angiography avoids arterial puncture. By using precisely timed intravenous contrast injection, multidetector (16 or 64 channel) CT scanners can generate angiographic images of excellent resolution and at a relatively high acquisition speed. MDCT angiography carries the contrast-related risks described above.^[20]

Carbon dioxide angiography

Carbon dioxide angiography is an alternative for patients with renal insufficiency; however, it is not widely available and requires some iodinated contrast material in addition to the carbon dioxide gas in order to provide useful images.

Transcutaneous tissue oxygen studies are reserved for borderline situations in which the advisability of arterial bypass surgery may be unclear.

Stage diabetic foot wounds based on the depth of soft tissue and osseous involvement.^{[2, 3, 4]} Any ulcer that seems to track into or is deep to the subcutaneous tissues should be probed gently, and if bone is encountered, osteomyelitis is likely.