Diabetic Neuropathic Foot Ulcers

Neuropathic foot ulcers form as a result of a loss of peripheral sensation and are typically seen in individuals with diabetes. Local paresthesias, or lack of sensation, over pressure points on the foot leads to extended microtrauma, breakdown of overlying tissue, and eventual ulceration. In addition, neuropathy can allow minor scrapes or cuts to go without proper treatment and eventually lead to the formation of foot ulcers. Typically, peripheral neuropathy affects the sensory nerves responsible for detecting sensations such as temperature or pain; however, it can also affect the motor nerves responsible for the contraction of muscles. Damage to motor nerves can lead to muscle wasting, resulting in a motor imbalance of flexor and extensor muscles that can result in foot deformities, such as claw toes or prominent metatarsal heads (the bones you feel under the ball of the foot). This then provides additional pressure points prone to ulceration. In addition to motor irregularities, ulceration frequently occurs at areas of high pressure on the surface of the foot, such as under the hallux (big toe), metatarsophalangeal joints (as mentioned above), the tops and ends of the toes, the middle and sides of the foot and the heel. Diabetic foot ulcers are typically a result of poor-fitting footwear, and regular visits to a podiatrist and pedorthist are recommended to help prevent foot ulceration from occurring.

Symptoms of Neuropathic Foot Ulcers

The appearance of neuropathic foot ulcers will vary based on the location and patient’s circulation and can appear as calloused blisters to open sores that are reddish to brown/black. The wound margins are usually undermined or macerated, and the surrounding skin will often be calloused, with the depth of the wound dependent on the amount of trauma the skin has be subjected to. Often, the undermining at the edges of the foot ulcer creates areas where infection can develop, which may lead to osteomyelitis (infection of the bone or bone marrow) if left untreated. The combination of pressure-related ischemia (restriction in the blood supply), neuropathy, and a delayed healing response response can allow infection to worsen before being treated when compared to other types of ulcers. The ulcer itself will typically be painless unless there is also infection or an arterial component to the wound that often only produces a minor discomfort. The limb will generally maintain a normal pulse, barring additional circulatory components to the neuropathic foot ulcer and patients often do not develop a fever in response to an infection.

Etiology

As mentioned above, neuropathic ulcers are caused by repeated stress on feet that have diminished sensation. However, if there is accompanying vascular impairment, the risk of amputation from an infection increases significantly and the ulcers appear more dry and punched out and form in areas less noted for pressure such as the sides of the foot or the digits. Neuropathic ulcers are multifactoral or caused by combination of many factors however neuropathy is a common factor in almost all of these wounds.

In addition to diabetes, other common factors that can cause peripheral neuropathy are:

• A primary neurological condition
• Alcoholic neuropathy
• Renal failure
• Herniated discs or spinal abnormalities
• Trauma
• Surgery

Some less common conditions that can lead to neuropathic ulcers are chronic leprosy, spina bifida, and syringomyelia.

Risk Factors

• Poor glycemic control
• Hypertension
• Hypercholesterolemia
• Kidney disease
• Smoking
• Foot deformities i.e. flatfoot, hammertoes, bunions, etc

Complications

Left untreated, neuropathic foot ulcers can lead to serious complications, including infection, tissue necrosis, and in extreme cases amputation of the affected limb.

Diagnostic Studies

• Peripheral nerve screening (Semmes Weinstein Filament Testing)
• Computed tomography (CT scan)
• Magnetic resonanace imaging (MRI)
• Electromyography
• Nerve conduction velocity
• Nerve biopsy
• Skin biopsy
• Wound cultures

Treatments of Neuropathic Foot Ulcers

The following precautions can help minimize the risk of developing neuropathic ulcers in at-risk patients and to minimize complications in patients already exhibiting symptoms:

• Consider regular podiatric care to remove excessive callouses and monitor for potential foot ulcerations.
• Examine feet daily for any unusual changes in color , temperature, or the development of sores or callouses.
• Ensure that footwear is properly fitted to avoid points of rubbing or pressure and to allow adequate room for any deformities by consulting a podiatrist or pedorthist.
• Protect feet from injury, infection and extreme temperatures.
• Never walk barefoot or wear open toed shoes or sandals. Wear your shoes or at the very least slippers while in the house.
• Avoid soaking feet. Insensate feet can easily be scalded without the patient realizing it.
• Manage diabetes or other applicable health conditions to expedite the healing process.

The first step in healing a diabetic neuropathic ulcer is to debride the wound down to healthy, bleeding tissue. Often there is infection underneath the superficial layer of necrotic tissue, even extending down into the bone and bone marrow. Debridement allows for better assessment of the ulcer and any underlying infections, as well as providing a better healing environment. Ideally, the wound environment should be moist while healing, but also allowed to breathe. The exact properties of the dressing used should be matched to those of the wound by your physician or wound care specialist.

One of the most essential components to effectively healing neuropathic ulcers is to reduce pressure on the affected area. However, relieving pressure from the wound needs to be balanced with encouraging proper circulation to the extremities, so excessive bed rest is not recommended. Contact casts or removable cast boots can be used to decrease pressure on the affected area while allowing the patient to remain ambulatory. Therapeutic shoes are also available to serve the same purpose, but are typically used for prevention or to avoid recurrence as opposed to during treatment.

If the ulcer does not resolve after more conservative measures, surgery to apply cellular or acellular tissue supplements, or correct deformities in the foot may be considered to remove excessive pressure.

Image Source: Medetec (www.medetec.co.uk). Used with permission.

References

Boulton AJM, Kirsner RS, Vileikyte L. "Neuropathic Diabetic Foot Ulcers." N Engl J Med 2004; 351:48-55. doi: 10.1056/NEJMcp032966

Cleveland Clinic. Lower Extremity (Leg and Foot) Ulcers. Cleveland Clinic. http://my.clevelandclinic.org/heart/disorders/vascular/legfootulcer.aspx. Updated November 2010. Accessed September 26, 2012.

Gabriel A. Vascular Ulcers. Medscape Reference. http://emedicine.medscape.com/article/1298345-overview. Updated July 11, 2012. Accessed September 26, 2012.

London Health Sciences Centre. Diabetic/Neuropathic Ulcer. London Health Sciences Centre. http://www.lhsc.on.ca/Health_Professionals/Wound_Care/diabetic.htm. Accessed September 26, 2012.

Mayo Foundation for Medical Education and Research. Diabetic neuropathy. Mayo Clinic. www.mayoclinic.com/health/diabetic-neuropathy/DS01045. Published March 6, 2012. Accessed September 26, 2012.

McGuire J. Transitional off-loading: an evidence-based approach to pressure redistribution in the diabetic foot. Advances Skin Wound Care. 2010; 23(4):175-8.

Takahashi P. Chronic Ischemic, Venous, and Neuropathic Ulcers in Long-Term Care. Annals of Long-Term Care. http://www.annalsoflongtermcare.com/article/5980. Published September 5, 2008. Accessed September 26, 2012.