Remote Temperature Monitoring in Diabetic Foot Ulcer Detection

Introduction. Diabetic foot ulcers (DFUs) are associated with increased morbidity, mortality, and resource utilization. Remote temperature monitoring (RTM) is an evidence-based and recommended component of standard preventative foot care for high-risk populations that can detect the inflammation preceding and accompanying DFUs. Objective. This case series illustrates the use of a RTM foot mat for the early detection and prevention of DFUs in patients with a history of DFUs. Materials and Methods. Three patients with a history of diabetes, neuropathy, and DFUs were provided a RTM foot mat and instructed in its daily use. Persistent localized temperature differences exceeding 1.75˚C between the left and right feet prompted the clinical staff to call the patient to collect subjective history for further triage. Results. Each patient presented with persistent temperature differences exceeding 1.75˚C. In one case, the patient was instructed to offload, and during a subsequent clinical exam, a callus was debrided and accommodative insoles were issued, resulting in resolution of the temperature differences. In the other 2 cases, the RTM foot mat prompted communication with and examination of the patient when there was damaged tissue deep to callus, resulting in early detection and treatment of uninfected DFUs. Conclusions. The findings of this case series are consistent with literature supporting the use of RTM for high-risk patients. 

Diabetic foot ulcers (DFUs) are associated with increased morbidity, mortality, and resource utilization.^1-3 Several clinical practice guidelines^4-7 recommend thermometry for high-risk patients, which is effective for early detection and prevention of DFUs when used to prompt timely noninvasive intervention such as pressure offloading.^8-10 A recent investigation¹¹ suggests remote temperature monitoring (RTM) by a smart thermometric foot mat (Podimetrics Mat; Podimetrics, Inc, Somerville, MA) may detect inflammation preceding a DFU at an average of 5 weeks prior to clinical presentation.

The objective of this case series is to explore the clinical value of remote thermometry for early inflammation detection in high-risk patients.

Three patients were chosen via retrospective chart analysis from the authors’ high-risk podiatry clinic. These patients had previously been prescribed a daily-use, thermometric, telemedicine smart foot mat for the home as an adjunct to standard preventative foot care. To qualify for the RTM mat, a patient must have at least 3 of the following: history of foot ulceration, history of amputation, foot deformity, peripheral vascular impairment, or peripheral neuropathy.

Patients were instructed to stand on the mat barefoot for 20 seconds at about the same time each day (Figure 1A). The thermometric data collected by the mat are referred to as scans and are transmitted remotely via opaque identifiers. Clinical staff can access foot temperature maps, or thermograms, derived from the scans through a secure online physician portal for triage (Figure 1B). These data are used in conjunction with health care providers to counsel patients and are recorded in their medical records via clinician note. All data collected, used, and presented herein have been de-identified in accordance with best practices and federal and local regulations.¹² 

The temperature data collected by the mat are automatically analyzed for temperature differences, or asymmetry, between the left and right feet at 6 locations: heel; arch; first, third, and fifth metatarsal heads; and the hallux.^8-10 A patient with temperature asymmetry exceeding 1.75˚C over 2 or more consecutive uses at the same location triggers a notification to the clinical staff, after which the patient is considered in episode. The patient is then monitored more aggressively for the subsequent 2 weeks, at minimum. A phone call is made to the patient to encourage proper offloading, decreased ambulation, elevation of feet, self-exam, and, if indicated by the subjective information, clinical exam. Asymmetry episodes resolve after 2 weeks of scans under the 1.75˚C threshold. 

All events and timelines were indexed from the time the patient completed the first scan after receiving the mat.

This case series does not constitute research due to its small size and lack of a testable scientific hypothesis. In addition, because thermometry is a recommended component of standard care, and the device studied is cleared by the US Food and Drug Administration (K150557) for an intended use consistent with the methods described herein, there are no concerns of patient safety or ethical treatment to be evaluated. Thus, because it does not constitute research, this case series did not require evaluation by an institutional review board.¹²

This case series details 3 patients with a history of DFUs, elevated hemoglobin (HbA_1c), and peripheral neuropathy.

Case 1

The first case is of a 67-year-old man with type 2 diabetes mellitus (DM; HbA_1c, 8.5%), neuropathy, and gout. The patient has extensive DFU history, including several recurrent wounds. The left distal third digit most recently healed 2 years prior to receiving the mat, and the right distal second digit healed 1 year prior to receiving the mat. 

Fourteen weeks after receiving the mat, the patient entered an episode with temperature asymmetry of 2.1˚C at the right hallux (Figure 2A). During a call prompted by the notification, the patient inspected his feet and denied any plantar lesions. Upon clinical exam 1 week later, no wounds were found. Accommodative insoles were dispensed. A second phone call was made during week 16 for continued elevated asymmetry of 1.8˚C at the right hallux (Figure 2B). The patient was seen in the clinic 5 days later without a DFU (Figure 2C). A callus to the distal left third digit was pared without incident. The patient’s asymmetry episode resolved during week 20 (Figure 2D). 

Case 2

Case 2 is of an 80-year-old man with type 2 DM (HbA_1c, 7.7%), neuropathy, and a history of a right plantar hallux wound that healed 9 months prior to receiving the mat (Figure 3A). Three weeks later, he entered an episode with temperature asymmetry of 6.0˚C and 8.2˚C on 2 consecutive days throughout the left forefoot (Figure 3B). During a call prompted by the asymmetry, the patient was instructed to decrease walking and use appropriate footwear. One week later, the patient remained in episode with asymmetry of nearly 4.7˚C, now over the right foot. The patient presented to the clinic 3 days later with a pinpoint DFU to the plantar and medial aspect of the right hallux interphalangeal joint (IPJ) postdebridement. A custom offloading orthotic was prescribed to fit his diabetic shoes.  

Between weeks 6 and 7, the patient was again found to have temperature asymmetry at the right forefoot, this time exceeding 3˚C. Upon exam during a clinic visit at the end of week 7, the patient’s right IPJ wound was healed. 

Despite this, the patient remained in episode through week 11, with temperature asymmetry exceeding 6.0˚C to the right forefoot and hallux (Figure 3C). The patient presented to the clinic at the end of week 11 wearing sandals without appropriate offloading. A pre-ulcerative callus to the area of concern was noted. Upon debridement, the plantarmedial area of the right hallux IPJ showed a deep tissue injury. The patient was reminded of the importance of offloading, and metatarsal bars were added to the patient’s sandals. The patient was casted for custom orthotics with an offloading accommodation at the hallux IPJ. The patient’s asymmetry episode resolved shortly thereafter, and he has remained out of asymmetry episode and free from DFUs over the following 22 weeks (Figure 3D).  

Case 3

The third case is of a 69-year-old man with type 2 DM (HbA1c, 12.3%), neuropathy, and peripheral arterial disease. The patient had a history of a DFU at the right plantar transmetatarsal amputation stump, most recently healed 3 weeks prior to receipt of the mat. 

The patient entered asymmetry episode on day 1 and remained in episode for the following 2 weeks (Figure 4A). He presented to the clinic on day 14 with a DFU measuring 1.2 cm x 0.8 cm x 0.2 cm upon debridement (Figure 4B). Patient denied prior knowledge of wound or lesion. Continued offloading and wound care resulted in closure about 9 months after receiving the mat. 

Thermometry is evidence-based and supported by randomized controlled trials.^8-11 These trials found a large treatment effect (62%–90% relative risk reduction for DFU incidence) using thermometry to prompt reduced ambulation for patients with temperature differences between contralateral locations on the feet exceeding 2.2˚C over 2 consecutive days. Building on this research, the smart foot mat in this case series was validated as part of a 129-participant study¹¹ on the basis of patient adherence in the daily use of the device and accuracy for predicting DFUs before clinical presentation. Daily adherence was encouraging, with 86% of the cohort averaging at least 3 uses per week. In terms of accuracy, the researchers found that the mat predicted 97% of nonacute plantar DFUs with an average lead time of approximately 5 weeks using the aforementioned 2.2˚C detection threshold and protocol.¹¹ At this sensitivity, the specificity was reported to be 43%. Although this represents a high false positive rate, the potential benefits of preventing a DFU exceed the cost of the intervention, which is inexpensive and noninvasive. In addition, the etiology of plantar inflammation is multifactorial, and the validation study only considered a DFU as an outcome and no other conditions, such as infection and callus, for which early intervention may be helpful. As a result, the patients in this case series were followed with an even more sensitive threshold of 1.75˚C, at which the investigators report a sensitivity of 100%, specificity of 25%, and an average lead time of 42 days.¹³

Research suggests that as many as 50% of patients who heal from a DFU experience recurrence within 2 years.¹¹ Although case 1 had multiple risk factors, including several new and recurrent DFUs and a history of amputation in the 2 years prior to receiving the mat, he has remained free of DFUs in the 34 weeks after beginning preventative thermometric monitoring. While being monitored, the patient entered asymmetry episodes that prompted offloading instructions, clinical exams, callus debridement, and issuance of accommodative insoles, after which the asymmetry episode resolved. This potentially indicates an effective preventative intervention regimen.

Multiple recent studies^14-16 have explored how wound healing is impacted by both the timeliness of initial treatment and the severity of the wound at initial presentation. These case studies highlight the promise of early detection for improved patient outcomes, especially when considering 100% sensitivity and 25% specificity at the 1.75˚C threshold.¹³ 

Both case 2 and case 3 herein presented with DFUs during asymmetry episodes. The patient of case 2 had a persistent episode lasting 12 weeks notable for 2 superficial wounds with hyperkeratotic tissue covering. This episode resolved only after the patient was issued metatarsal bars for his sandals and custom orthotics, potentially indicating an effective offloading intervention that allowed proper healing of the deep tissue injury. The evolution of the episode in case 3 suggests the DFU may have been developing prior to receipt of the mat despite the normal clinical exam on day 0. In both of these cases, the episodes prompted communication with and examination of the patient at a time when the patients had damaged tissue deep to callus, and all 3 DFUs were of low severity (University of Texas Diabetic Wound Classification 1A) at presentation. Early detection due to thermometric monitoring may have resulted in early intervention for both patients, potentially shortening DFU course and reducing morbidity, mortality, and resource utilization.

The authors acknowledge that this is a small case series limited by its size and lack of quantified comparator. Although thermometry is recommended by several practice guidelines^5-7 and outcomes trials^8-11 characterizing its effectiveness, the study device has only been validated for its predictive accuracy. More research with a larger cohort is needed to expand the indication of use to comprise other inflammatory conditions, including Charcot.  

Results of this case series support the use of RTM by a smart thermometric foot mat for the early identification of inflammation to prompt clinical evaluation and intervention. Although this case series is limited in scope by its small sample size, the findings are consistent with literature suggesting the value of daily foot temperature monitoring for high-risk patients.^8-10

Affiliation: Department of Surgery, Podiatry Section, Southern Arizona Veteran Affairs Health Care System, Tucson, AZ

Correspondence: Jodi L. Walters, DPM, DABFAS, Department of Surgery, Podiatry Section, Southern Arizona Veteran Affairs Health Care System, 3601 South 6th Avenue, Tucson, AZ 85723;
Jodi.Walters@va.gov

Disclosure: The authors report no financial or other conflicts of interest. This paper was presented as a poster at the Fall 2017 Symposium on Advanced Wound Care in Las Vegas, NV.