An In-Home Telemedicine System to Detect Inflammation in Patients with a Recently-Closed Diabetic Foot UlcerRobert G. Frykberg, DPM, MPHa; Ian L. Gordon, MDb; Jonathan D. Bloom, MDc; Brian J. Petersen, MS, MBAc;

Aksone Novoung, DPMd; David R. Linders, MS, MBAc; The Smart Foot Mat Research Groupe

Diabetic Foot Ulcers (DFU) are known to be associated with increased morbidity,mortality, and resource utilization, with up to 33% of all direct costs in diabetes linked totheir treatment [1]. Though all patients with diabetes are at risk to develop a DFU, thegroup at greatest risk are those patients who have recently healed from a previous DFUepisode. A principal goal of care for these patients is to maintain the integrity of thenewly-formed epithelium and allow the underlying tissue to complete remodeling.

Numerous prospective studies have explored how a patient’s ulcer free survival isimpacted by the duration since a previous ulcer has healed [2-5]. These investigationssuggest that between 30% and 40% of patients experience a recurrent DFU in the firstyear after healing. This is in stark contrast to a baseline rate among all patients withdiabetes, which has been estimated to be between 3.6-5.8% [6-8]. A system that canprevent DFU recurrence during this critical period, therefore, has the potential tosignificantly improve patient outcomes and reduce DFU-related resource utilization.

Dermal thermometry first emerged in the 1970s as a useful tool for identifying foot tissueat risk for breakdown and ulceration. Three randomized controlled trials [9-11] haveinvestigated the benefit of early offloading in the presence of an elevated plantar skintemperature and have demonstrated an approximately 70% reduction in plantar DFUrecurrence. However, the recently-closed DFU may propose a challenge forconventional thermometric monitoring because elevated localized skin temperatures maybe present during normal healing.

The purpose of this study is to determine the accuracy of pre-ulcer detection in patientswith a recently closed DFU (within the previous 3 months). The Podimetrics Mat[Figure 1] is an in-home telemedicine device that has been previously investigated forprediction of impending DFU through the remote daily monitoring of plantar foottemperatures. We examine its predictive accuracy in patients with recently-closedulcers.

For this analysis, we considered only those subjects who achieved closure from aprevious DFU episode within the three months prior to enrollment. Thermometric datafrom these subjects were analyzed in accordance with the approach proposed by Laveryand colleagues [9]. This approach compares the temperatures between the left foot andright foot at six plantar locations (the hallux, first, third and fifth metatarsal heads, arch,and heel). Offloading interventions have been demonstrated effective for DFUprevention in subjects who exhibit a persistent temperature asymmetry at any of theselocations. Traditionally, the threshold used is 2.22° C over two days; however, for thisanalysis, four asymmetry thresholds were chosen for comparison, and the sensitivity andspecificity for each threshold are reported as averages over randomly-sampled twomonth intervals.

Figure 2 compares the the thermographic history of two subjects The left portion of thefigure shows thermometric data from Subject I, a 58 year old male with a history ofamputations for DFU to the right 4th and 5th and left 2nd and 3rd digits, with the lastincision healing 12 weeks prior to enrollment. At no point during study participation didhe exceed a temperature asymmetry of 2.22° C or experience a new DFU.

Methods

Background

Results

Author Information & References

Conclusions

Table 1 All Subjects Without DFU With DFU

Number 40 25 (62.5%) 15 (37.5%)

Age 59.4 (± 12.2) 56.7 (± 13.5) 63.8 (± 8.2)

% Male 80.0% (32/40) 88.0% (22/25) 66.7% (10/15)

Last Ulcer Healed (months) 1.2 (± 0.9) 1.1 (± 0.9) 1.2 (± 0.9)

Diabetes Diagnosis (years) 18.0 (± 11.8) 14.3 (± 9.7) 23.7 (± 12.8)

Percent insulin dependent 52.5% (21/40) 44.0% (11/25) 66.7% (10/15)

HbA1c 8.8 (± 2.3) 9.0 (+/- 2.6) 8.4 (± 2.0)

BMI 34.0 (± 6.1) 33.6 (± 6.2) 34.5 (± 6.0)

Average adherence, uses/week 5.4 (± 1.2) 5.4 (± 1.3) 5.4 (± 1.1)

Forty subjects with recently closed DFU were included [Table 1]. Recurrence wasobserved in 15 subjects (37.5%). Average adherence in daily use of the Podimetrics matacross the forty subjects was 5.4 days/week.

a. Carl T. Hayden Veterans Affairs Medical Center, Phoenix, AZ; b. Long Beach Veterans Affairs MedicalCenter, Long Beach, CA; c. Podimetrics, Inc., Somerville, MA; d. Western University of Health Sciences,Pamona, CA; e. additional members include Gary Rothenberg, DPM, Bijan Najafi, PhD, Alex Reyzelman,DPM, Shawn Cazzell, DPM, Ryan Fitzgerald, DPM;

These data suggest the Podimetrics Mat may be useful for identifying patients shortlyafter wound closure who are at risk of recurrence despite the presence of possibleunderlying inflammation that may be the result of the normal healing process. As a result,use of such a system in this population may result in significant reductions in DFU-related morbidity, mortality, and resource utilization.

Table 2 Asymmetry (° C) Sensitivity Specificity

Lavery 2004 2.22 100% 35%

Threshold 1 2.75 86% 53%

Threshold 2 3.20 65% 67%

Threshold 3 3.75 53% 78%

The sensitivity and specificity of the system are reported in Table 2 for four temperatureasymmetry thresholds. The AUC of the ROC curve was 0.78. At the 2.22° C thresholdused by Lavery and colleagues, all subjects who developed an ulcer were identified withan average lead-time (between alert and clinical presentation) of 36 ± 17 days,respectively. At the higher threshold of 3.2° C, the sensitivity and specificity are bothapproximately 65%, and alert lead-time was 41 ± 18 days.

Patients were enrolled as part of a multicenter cohort trial following 129 subjects for 34weeks each. Principal enrollment criteria included history of plantar DFU and absenceof active foot pathology such as Charcot arthropathy. Enrolled subjects were provided aPodimetrics Mat and instructed to use it daily. The primary outcome of interest wasoccurrence of plantar DFU. Secondary outcomes included subject adherence in the dailyuse of the Podimetrics Mat.

Subject II, whose data is shown in the right portion of the figure, is a 59 year old femalesubject with a history of DFU on her right hallux and right 5th metatarsal head, the latterof which closed approximately 11 weeks prior to enrollment. Temperature asymmetryexceeded 2.2°C at multiple time periods during participation, and her right fifthmetatarsal head DFU recurred by week 10.

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