New Risk Score for Amputation in Infected Diabetic Foot Ulcers

Becky McCall

February 24, 2015

A new risk score for amputation in patients with infected diabetic foot ulcers that could be used easily in daily practice has been developed, with the researchers claiming it may have better prognostic accuracy than the current International Working Group on the Diabetic Foot (IWGDF) classification system.

The Eurodiale score, as it is currently referred to, was developed on the basis of results from the largest study of its kind to date, led by Dr Kristy Pickwell (Maastricht University Medical Center, the Netherlands) and published online February 9 in Diabetes Care.

"Our study suggests that a small number of variables, readily obtained in a clinician's office, can accurately predict risk of amputation and help guide clinicians with choice of therapy in patients with an infected diabetic foot ulcer," Dr Pickwell told Medscape Medical News.

For example, "Can someone be treated as an outpatient with oral antibiotics, or should they be treated in the hospital with bed rest and intravenous antibiotics?" she explained.

According to Dr Pickwell, the IWGDF classification predicts amputation, but it can require additional laboratory tests, the results of which are not immediately available. Also, it focuses on the infection and does not take into account other factors, such as patient demographics and comorbidities, that are also known to influence the risk of amputation.

With this in mind, Dr Pickwell and her colleagues from across Europe aimed to identify the most important factors that can both accurately predict the risk of amputation and be easily obtained in a clinical setting — among other things, they pinpointed presence of edema and ulcer depth as being indicators.

Asked to comment on the new paper, Dr Dane K Wukich (UPMC Mercy Center for Healing and Amputation Prevention and Comprehensive Foot & Ankle Center, Pittsburgh, Pennsylvania) welcomed the work, noting that amputation prevention is very important

"Patients with diabetic foot infections may not manifest some of the classic signs of severe infection, and consequently, physicians may not appreciate how sick these patients are. The researchers have identified important predictors of amputation, and we need to be on high alert — if patients present with the clinical signs they mentioned, we should be very aggressive," he said.

Study Aim and Design

The Eurodiale study comprised a relatively large cohort of 575 patients with infected diabetic foot ulcers presenting to one of 14 diabetic foot clinics in 10 European countries.

Prior studies of this nature have contained fewer patients with infected diabetic foot ulcers (100 and 165 patients, respectively) or assessed only patients with large (at least 3 x 3 cm) and deep ulcers, the researchers note.

Amputations were divided into two categories: patients having any amputation; and those having amputations of the big toe and above (so including amputations of part of the foot and the lower leg).

In the second category, amputations of digits 2 to 5 (the lesser toes) were excluded; amputations of the big toe and above are the most severe amputations with the most profound influence on mobility, so leaving the lesser toes intact means patients are still able to be receive well-fitting shoes, Dr Pickwell explained.

Patients were followed monthly until healing of the foot ulcer(s), major amputation, or death, up to a maximum of one year. Only data from patients with an infected foot ulcer diagnosed by the IWGDF/Infectious Disease Society of America (IDSA) guidelines were analyzed.

The researchers assessed associations between the 1-year amputation incidence and patient, leg, ulcer, and infection characteristics, including sex; age; immobility; serum creatinine; HbA1c; presence of peripheral arterial disease (PAD) and polyneuropathy; ulcer size, depth, duration, and location; periwound redness; periwound edema; pain; foul smell; exudate/pus; increased local skin temperature; lymphadenitis/lymphangitis; fever; and C-reactive protein (CRP).

Edema, Ulcer Depth, and Elevated CRP Among Predictors of Amputation

Of the 575 patients with infected diabetic foot ulcers assessed, amputations were performed on 159 (28%) of them within the year of follow-up.

"We found that several factors independently predicted amputation in patients with an infected diabetic foot ulcer," reported Dr Pickwell.

The independent risk factors for lower-extremity amputation were, in decreasing order of hazard ratio: positive probe-to-bone test, deep ulcer, elevated CRP levels, and the presence of periwound or pretibial edema.

The presence of increased nonpurulent exudate, foul smell, and fever independently predicted any amputation, but not amputations excluding the lesser toes.

Periwound and pretibial edema, as well as the presence of increased exudate, have not previously been associated with amputation, the researchers note.

Increasing IWGDF severity of infection also independently predicted amputation.

The results confirmed some of the risk factors identified in previous studies, but not others, the authors say.

Greater Prognostic Accuracy of the New Eurodiale Score

They developed the Eurodiale risk score for both kinds of amputation — including the variables sex, pain on palpation, periwound edema, ulcer size, ulcer depth, and peripheral arterial disease — and this predicted amputation better than the IWGDF system (area under the receiver operating characteristics (ROC) curves 0.80, 0.78, and 0.67, respectively).

"The [Eurodiale] risk score for any amputation had a scale of 0 to 4.5. We found that 6% of patients with a score of 1.5 or less underwent any amputation, whereas 50% of patients with a score between 3 and 4.5 underwent any amputation," reported Dr Pickwell.

For the second, more severe category of amputations, there was a scale of 0 to 6.5. The researchers found that 1% of patients with a score of 2 or less underwent an amputation of the big toe and above, whereas 39% of patients with a score between 4.5 and 6.5 underwent such an amputation.

As well as developing the new risk score, Dr Pickwell and her colleagues validated the prognostic value of the IWGDF classification system.

The ROC curve for the new risk scores (referring to any amputation and amputation including big toe and above) had a larger area under the curve than the IWGDF classification: 0.80 and 0.78 vs 0.67, respectively.

However, "It should be noted that these Eurodiale scores were developed based on the available data of our cohort, and they will need to be validated in other populations before any firm conclusions can be drawn," they point out.

"A Step Forward"

Explaining why he believes this new risk score is a step forward, Dr Wukich said that the IWGDF classification, which is similar to the IDSA, categorizes infection based on severity.

"It really didn't stratify the risk of amputation…this manuscript does that."

He remarked that he would definitely incorporate this new system once it was further validated.

The study was supported by the Fifth Framework Programme of the European Commission. Dr Pickwell and coauthors have reported no relevant financial relationships, as has Dr Wukich.

Diabetes Care. Published online February 9, 2015. Abstract

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