Diabetic Foot

Peripheral arterial occlusive disease is 4x more prevalent in diabetics than in nondiabetics. It tends to occur at an earlier age in diabetics, and the risk of disease increases with the duration of diabetes.

The calcification of atherosclerotic plaques in arteries of diabetic patients is more diffuse and occurs within the tunica media of the arteries, producing a lead pipe appearance on plain radiographs (as opposed to plaques in nondiabetic patients, which are patchy and occur in the tunica intima).

The arterial occlusion of the proximal large vessels is similar to that in nondiabetics; however, the macrovascular disease is more diffuse in diabetics distal to the popliteal trifurcation. Distal vascular procedures have proven to be helpful in diabetic patients.

Microvascular complications of diabetes (neuropathy, retinopathy, and nephropathy) and macrovascular complications (peripheral vascular disease, coronary artery disease, hypertension, hyperlipidemia, and cerebrovascular disease) together contribute to diabetic foot problems.

A detailed history should be obtained, including a history of smoking, hypertension, and hyperlipidemia. Patients with advanced disease will complain of claudication.

Pain due to vascular claudication is usually relieved with rest. However, ischemic foot pain can also occur at rest.

On physical examination, absent popliteal or posterior tibial pulses, thin or shiny skin, absence of hair on the foot or leg, thickened nails, and dependent rubor are all signs of vascular insufficiency.

Any patient with signs of advanced vascular disease (such as a history of claudication, nonhealing ulcers, or nonpalpable pulses) should be evaluated by a vascular specialist.

Noninvasive vascular tests include the ankle-brachial index (ABI) using Doppler ultrasound pressures, transcutaneous oxygen (TcpO2) measurement (oximetry), the absolute toe systolic pressure (plethysmography), Doppler waveform analysis, and segmental Doppler limb pressures and pulse volume recordings.

Arterial pressure readings can be falsely elevated due to rigid arterial calcification in diabetics, which may artificially raise the ABI to > 1.00. Despite that, an ABI of < 0.80 is generally considered abnormal and < 0.45 in a diabetic patient is suggestive of limb-threatening ischemia.

Absolute toe pressures may be more predictive of distal wound healing with toe systolic pressure < 45 mm Hg indicating poor wound-healing potential and < 30 mm Hg indicating critical limb ischemia.

Transcutaneous oxygen measurement < 20-30 mm Hg represents poor wound-healing potential.

When assessing Doppler waveform recordings, a triphasic waveform is normal. Biphasic (loss of reverse flow in early diastole) and monophasic waveforms suggest advanced occlusive disease. If lower extremity ischemia is strongly suspected, arteriography, magnetic resonance angiography, or computed tomography angiography should be performed to assess the vascular flow.

Peripheral neuropathy is the most common cause of diabetic foot complications. The presence of neuropathy (diabetic or otherwise) greatly increases the risk of complications from any surgery.

Diabetic neuropathy can involve the sensory, motor, and autonomic pathways.

Diabetic neuropathy has been estimated to occur in 58% of patients with longstanding disease, although 1 study noted that close to 80% of diabetic patients having surgery had some degree of neuropathy.

The earliest finding in diabetic neuropathy is vibratory and proprioceptive loss. Signs and symptoms are variable but include paresthesias, burning sensations, hyperpathia, and dysesthesias and usually reveal a symmetric sensory loss in a "stocking-glove" distribution.

Due to the loss of protective (pain) sensation, foot ulceration generally occurs by repetitive trauma in areas of high mechanical pressure.

The 5.07 (10-g monofilament) Semmes-Weinstein monofilament (SWM) test of 7-10 plantar foot sites is the recommended screening test for a patient at risk for ulcer formation due to loss of protective sensation. However, up to 10% of patients who pass the SWM test may still develop skin breakdown.

A simplified screening test has been described. If a patient cannot sense the touch of a 4.5-g/4.65 SWM when it is pressed under the 1st metatarsal head with just enough pressure to bend the filament, the patient should be considered at risk for ulceration.

Denervation of the eccrine and apocrine glands and arteries leads to abnormal thermoregulation and interference with the normal hyperemic response to infection.

There is decreased sweating and loss of skin temperature regulation, causing dry, cracked skin and fissure formation, which predispose to infection by allowing a portal for bacterial entry.

Autonomic neuropathy can also cause orthostatic hypotension; cardiovascular, urinary, and gastrointestinal problems; and erectile dysfunction. It may produce chronic venous swelling, usually requiring management with compression stockings.