'Smart Mat' Predicts 97% of Recurrent Diabetic Foot Ulcers

Becky McCall

May 10, 2017

A novel wireless foot-temperature–monitoring system (Podimetrics) aimed at detecting impending diabetic foot ulcers (DFUs) through plantar temperature change is highly predictive of recurrent DFUs, according to new findings from a multicenter, prospective, cohort study in a high-risk population.

The temperature-monitoring mat was able to correctly detect 97% of impending nontraumatic DFUs in patients who had had prior ulcers.

"We showed that using this wireless mat and an algorithm that detects temperature rise over several days, it is possible to detect development of an ulcer 5 weeks in advance," reported Robert Frykberg, DPM, podiatrist at Phoenix VA Healthcare System, Arizona, and lead investigator of the study that was published May 2 in Diabetes Care.

However, although there was a high rate of detection of ulcers, this was accompanied by a high false-positive rate of 57%, the authors note, adding that the protocol might need to be tweaked to try to reduce this.

Temperature Monitoring Recommended, but Lack of Good Technology

Around 30 million patients have diabetes in the United States, and each year, approximately 1.7 million suffer one or more foot ulcers. And studies suggest between 30% and 40% of patients experience a recurrent DFU within 12 months of the initial ulcer healing, say Dr Frykberg and colleagues.

In order to reduce the rate of recurrent DFUs, US guidelines (J Foot Ankle Surg 2006;45[Suppl]:S1–S66) emphasize incorporating daily thermometry into standard preventive care. But its use remains uncommon in practice, they say, which "may be because of challenges with previous temperature-monitoring technologies, including onerous patient workflow and poor usability."

The system in this latest study comprises a wireless floor mat with an array of temperature sensors under a water-resistant cover. Patients are required to stand on the mat for 20 seconds per day to obtain plantar-temperature data that are transmitted wirelessly to the manufacturer's monitoring center.

By detecting the difference in plantar temperature between the two feet, it is possible to identify a patient with an elevated risk of impending DFU.

"Essentially, the mat detects areas of increased inflammation that often precede ulceration," explained Dr Frykberg. "It has been shown, in this and other studies, that when this device is used with early intervention, it can very likely reduce the development of recurrent ulcers."

This device, he adds, is very "user-friendly" as it "wirelessly transmits to a central monitoring service. We found very high adherence to use — 86% of patients averaged at least three uses per week."

Novel Aspect of Study: Different Temperature Thresholds Evaluated

Dr Frykberg and colleagues say that as the potential impact of temperature-guided avoidance therapy is already well established, the specific aim of this study was to address a knowledge gap: "the trade-off between sensitivity and specificity as a function of temperature-asymmetry threshold."

Data were evaluable from 129 patients who had a previously healed DFU, and they were followed up for 34 weeks.

The primary outcome was development of nontraumatic plantar DFU, and the primary efficacy analysis was the accuracy of the study device for predicting the occurrence of DFU over several temperature-asymmetry thresholds.

Adherence to daily use of the mat, device-related trips or falls, and device-related injury were secondary outcomes. Perceptions of the mat and ease of use were also assessed. And false-positive and false-negative rates were calculated over 2-month samples of participant data.

Plantar temperature asymmetry was found to be highly predictive of impending DFU. Using the standard "threshold" of a difference in temperature between the feet of 2.22°C, as used in previous studies, the mat detected 97% of nontraumatic DFUs five weeks before they presented clinically.

In total, 37 (28.7%) of patients with evaluable data presented with 53 DFUs.

Recognizing that there is clearly a need to diminish the false-positive rate of 57%, Dr Frykberg pointed out: "The standard temperature difference used was 2.22°C, but we can probably become more specific with new algorithms to eliminate many of these false positives."

The researchers did investigate other temperature thresholds, "a novel and previously unchartered aspect" of temperature monitoring of the diabetic foot, they observe. They found that increasing this threshold to 3.20°C decreased sensitivity to 70% but similarly reduced the false-positive rate to 32% with the same lead time of 37 days.

With respect to device adherence, approximately 86% of participants were found to use the system for an average of at least 3 days a week on average over the study.

Cost Considerations

Dr Frykberg stressed that the study was noninterventional and did not assess any potential reduction of DFU incidence and related costs.

"The cost of the device is far exceeded by one ulceration, particularly if it becomes infected," with the latter costing upward from $20,000, he asserted. In the long term, any price tag on the device would be "far preferable to the costs of managing ulceration," he added.

He also noted that at this point in development, the mat is intended for use only in high-risk patients, and that there are no data in the general diabetic population. "Nothing suggests it would not be effective, but there are no data to this effect yet."

Podimetrics funded this study as its sole sponsor, including providing the study devices and financial support to the clinical sites for study operations. Dr Frykberg declares no relevant financial relationships. Disclosures for the coauthors are listed in the paper.

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Diabetes Care. Published online May 2, 2017. Abstract

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