Diabetic foot ulcers challenge caregivers

Many untreated wounds lead to amputation

One reason for hospital admissions among patients with diabetes mellitus in the United States and Europe is foot ulceration. According to one source, 6% of people with diabetes admitted to hospitals annually in the United States are there because of a foot ulcer.1 And, says David Armstrong, DPM, assistant professor in the department of orthopedics at the University of Texas Health Science Center in San Antonio, 25% of all hospital admissions of diabetics in the United States and Britain are due to infected foot ulcers. Diabetic foot ulcers, if not promptly identified and addressed, are precursors to amputation.

The potential for widespread trouble becomes obvious when you know there are an estimated 16 million people with diabetes in the United States alone, and many of them don't do a good job of monitoring and controlling their blood glucose levels. According to research conducted by Michael Rudolph, PharmD, executive director of community practice at the University of Southern California in Los Angeles Researchers at the University of Southern California, one-third of diabetic patients don't even monitor their blood glucose levels.

Despite the prevalence of the disease, many misconceptions about the risk factors, assessment, and treatment of diabetic foot ulcers remain commonplace, according to specialists such as Jeffrey Jensen, DPM, clinic director of the Diabetic Foot and Wound Center in Denver. One such falsehood, he says, is the notion that patients with diabetes often have small-vessel disease in their lower extremities, which prevents wounds from healing.

"There's no such thing as small-vessel disease, yet some people still believe it is a factor in the healing of diabetic foot ulcers," Jensen says. In general, he adds, there is a dearth of solid clinical knowledge of how to deal with diabetic foot ulcers.

Medical and local factors

Risk factors for getting diabetic foot ulcers can be divided into the broad categories of medical factors and local factors, says Armstrong. Medical factors include:

· the length of time a patient has had diabetes;

· glucose control;

· gender.

Men are at greater risk than women for foot ulcers, primarily because they are less compliant with medical instructions and self-care procedures such as blood glucose monitoring and control. In addition, men participate less frequently in "wellness" visits than women.

Local factors include peripheral neuropathy and neuropathy accompanied by structural deformity. Neuropathy is clearly considered the most important risk factor linking diabetes to foot ulcers. One clinician defines neuropathy simply as "loss of protective sensation." The inability of many diabetic patients to feel pain in the lower extremities, of course, means they may not be aware of skin breakdown and incipient wound formation.

"We must teach patients and health care providers to be aware of and respond to the absence of pain," says Armstrong.

Researchers have found that the insensate foot is one of three independent predictors of foot ulceration. The others are absence of the Achilles tendon reflex and a transcutaneous oxygen tension of less than 30 mmHg,2 which is the strongest quantifiable predictor of all.

The Diabetes Control and Complications Trial found that 39% of the patients had clinical manifestations of diabetic neuropathy at the time they entered the study,3 says Marvin Levin, MD, professor of clinical medicine and the director of the Endocrinology, Diabetes and Metabolism Clinic at Washington University School of Medicine in St. Louis.

In another study cited by Levin, peripheral neuropathy was present in 60% of all patients with diabetic foot ulcers. Yet neuropathy does not preclude the simultaneous presence of painful symptoms, adds Levin. "I have found that the development of pain in a previously painless ulcer may indicate worsening infection and penetration into the deeper tissues of the foot, even though the ulcer appears unchanged," he writes.3

The most common sites of ulceration due to neuropathy are over the metatarsal heads and on the plantar surface of the great toe, says Levin. When the ulcer appears on the side of the foot, the most likely causes are ill-fitting shoes and ischemic-pressure necrosis.3

Deformity, amputation increase risk

Add deformity to the equation and the risk grows even greater. Armstrong says foot deformities result in areas of abnormal pedal pressure. These regions of focused stress are at increased risk for ulceration in the insensate foot.4 Deformities can include claw toes, hammer toes, cocked-up toes, and Charcot foot.

Another local factor is prior ulceration or amputation. "That person clearly has all of the ingredients to produce another [foot ulcer]," says Armstrong. He notes that patients with neuropathy, deformity, and a history of previous ulcers or amputation are nearly 36 times more likely to have an ulcer develop than are patients with diabetes without these risk factors.

Even amputation of a single toe can lead to subsequent deformities in adjoining toes and development of wounds, according to experts.

Risk factors for non-healing ulcers and amputation are slightly different but lie on the same continuum, according to Armstrong. A neuropathic ulcer is an important risk factor for amputation, as is infection, ischemia, and peripheral vascular disease. The latter is the only risk factor that can lead to amputation in and of itself, explains Armstrong. A foot ulcer can lead to amputation only if it becomes infected.

The University of Texas Diabetic Foot Classification System, formulated by Armstrong and his colleagues, summarizes the risk factors for diabetic foot ulcer development and for amputation. (See charts, p. 70.) Categories 0-4 deal with risk factors for ulcers; categories 5-8 cover risk factors for amputation.

References

1. Relber GE, Boyko J, Smith DG. Lower extremity foot ulcers and amputation in individuals with diabetes. In: Harris MI, Cowle CC, Stern MP, et al, editors. Diabetes in America. 2nd ed. Washington, DC: U.S. Government Printing Office, DHHS publ. No. 95-1468; 1995.

2. McNeely MJ, Boyko EJ, Ahroni JH, et al. The independent contributions of diabetic neuropathy and vasculopathy in foot ulceration: How great are the risks? Diab Care 1995; 18:216-219.

3. Levin M. Prevention and treatment of diabetic foot wounds. JWOCN 1998; 3:129-143.

4. Armstrong DG, Lavery LA, Wunderlich RP. Risk factors for diabetic foot ulceration: A logical approach to treatment. JWOCN 1998; 25:123-128.