Use of a Remote Temperature Monitoring Mat for the Early Identification of Foot Ulcers

Introduction. Diabetic foot ulcers (DFUs) are responsible for considerable morbidity, mortality, and cost. Remote temperature monitoring (RTM) is an evidenced-based and recommended component of standard foot care for at-risk patients. Although previous research has demonstrated the value of RTM for foot ulcer prevention, its benefits related to the early identification of diabetic foot complications may be underappreciated. Objective. This article presents a case series supporting the use of RTM for early identification of DFUs. Materials and Methods. The cases of 4 veteran patients who presented consecutively with inflammation, which was detected by a telemedicine temperature monitoring mat, are reported. The authors collected subjective history from each patient via telephone outreach and triaged these patients according to standard diabetic foot care recommendations. Results. Each patient required a clinical exam prompted by the mat and the patient’s subjective history. In each case, the patient required callus debridement upon which a pre-ulcerative lesion or partial-thickness wound was discovered. The DFUs in these 4 cases healed quickly and without complication. In 2 of the cases, the outreach prompted by the mat reestablished specialist foot care after a prolonged period without routine exam. Conclusions. In each of these cases, the RTM mat detected inflammation accompanying a preulcerative lesion or a partial-thickness wound, allowing for timely intervention and treatment, including debridement and offloading, which may have the potential to improve care and reduce morbidity, mortality, and costs. 

Diabetic foot ulcers (DFUs) are among the most devastating and costly sequelae of diabetes. Between 75% and 95% of all lower extremity amputations are preceded by a DFU,^1-7 and the mortality rates for those with incident DFUs are worse than for patients with most types of cancer.^8-13 

As a result, primary objectives of care for patients with diabetes are prevention and effective management of DFUs.¹⁴ Research suggests early identification of DFUs is a critical factor for ensuring good patient outcomes and containing costs.^15-21 Oyibo et al²² found a strong correlation between the severity of a DFU at presentation and subsequent amputation rate. In 2017, Smith-Strøm et al²³ concluded that “early detection and referral by both the patient and general practitioner are crucial for optimal foot ulcer healing.” It is estimated that more than two-thirds of the episodic costs of DFUs are attributable to hospitalization,^24-27 which is often an outcome of chronic DFUs.

Recently, the emergence of remote temperature monitoring (RTM) has offered an efficacious preventive option for diabetic foot care in high-risk patients.^28,29 The objective of RTM is to monitor dermal foot temperatures for thermal signs of inflammation; this allows the provision of targeted and timely interventions, such as debridement of callus, pressure offloading of the affected inflamed areas, and treatment of any wounds previously not possible to prevent the worst complications of DFUs. Remote temperature monitoring is supported by 3 randomized controlled trials,^30-32 which found a large treatment effect (62%–90% relative risk reduction in DFU incidence) when used to prompt reduced ambulation. Building on this research, an RTM foot mat recently was evaluated in a multicenter study following 129 patients, each followed for 34 weeks.³³ The investigators³³ found the mat predicted 97% of nonacute plantar DFUs, with an average lead time of about 5 weeks.

Although previous research has demonstrated the value of RTM for preventing foot ulcers, perhaps less appreciated are its benefits for the early identification of diabetic foot complications. With this in mind, the case series reported herein evaluated the use of RTM for early identification of DFUs in 4 at-risk patients. 

The authors followed 4 high-risk veteran patients who received care in a high-risk Veteran Health Administration (VHA) podiatry clinic in Phoenix, Arizona. These patients were prescribed an in-home telemedicine RTM mat (SmartMat; Podimetrics, Inc, Somerville, MA) for preventive foot care. At this clinic, patients with loss of protective sensation due to peripheral neuropathy are eligible for RTM with this mat.³⁴ 

The patients in this case series presented consecutively with large asymmetry during a 4-month period in 2018. Each case ultimately required clinical examination to resolve. During exam, each patient was found to have a preulcerative, subcallus lesion or partial-thickness wound. If gone undetected, this foot complication could gradually deepen due to prolonged, repetitive trauma and subsequently reach the tendon, bone, or joint, causing localized deep tissue abscess or osteomyelitis and amputation.

Methodology

The mat (Figure 1A) is intended to prompt communication between a patient and health care provider for further evaluation and treatment of persistent foot inflammation. It is a daily-use medical device indicated for patients at risk for inflammatory foot conditions. To use the mat, the patient must stand barefoot on the mat for 20 seconds daily. The entirety of its surface is covered with temperature sensors, allowing the temperature profile of both feet to be captured in the presence of foot deformity due to motor neuropathy and missing anatomy due to amputation history. The mat collects daily temperature measurements of the patient’s foot, or scans. Foot temperature maps, or thermograms, derived from the scans are available to the clinical staff via an online portal (Figure 1B) to inform clinical decision-making. The temperature data are analyzed automatically for temperature differences, or asymmetry, between the left and right feet to identify inflamed areas on the foot. A patient presenting with asymmetry exceeding 2.2°C (4°F) over 2 or more consecutive uses at the same location is deemed “in episode.” A phone call is made to the patient to encourage offloading through decreased ambulation (target 50% of baseline step count), conduct a self-examination of the feet (with the assistance of a caregiver, if possible), and, if indicated by the subjective exam, prompt a follow-up exam in the clinic. 

Conventions and definitions

For all thermograms included herein, the authors adopted the conventions previously defined by Frykberg et al³³ and Killeen and Walters.³⁵ The plantar aspect of the foot is viewed from below so that the right foot is at image left. Portions of the thermograms with lighter shades of color indicate higher temperatures, and on each thermogram, the color bar temperature range is centered at the mean temperature. Due to confounding factors affecting mean foot temperature, such as ambient temperature and time of day, the color bar for each thermogram has a unique dynamic temperature scale. Nonetheless, the temperature range (ie, the difference between the minimum and maximum temperatures encoded by the lightest and darkest hue colors) shown on each color bar are consistent across the thermograms, corresponding to a range encompassing 95% of thermogram temperatures observed by Frykberg et al.³³

The conventions and definitions of the International Working Group on the Diabetic Foot were used in this report.³⁶ The authors herein define a foot ulcer as a break in the skin of the foot penetrating through both the epidermis and a minimum amount of the dermis. Given their etiology, foot ulcers often present as a hemorrhagic callus or wounds underneath hyperkeratotic covering, which are revealed upon debridement. The authors consider a foot ulcer partial thickness if it extends no deeper than the dermis; a DFU is defined as a foot ulcer in a patient with diabetes. A foot ulcer is determined to be healed when it has completely epithelialized without any drainage. Further, the authors define a foot ulcer as non-infected if it is absent of clinical signs or symptoms of infection.

Ethics

The authors compiled these cases with the VHA Guidance on Case Reports³⁷ in mind to ensure ethical treatment of the patients included in this series. Consistent with this guidance, this case series did not constitute research due to its small size and lack of testable scientific hypothesis. Thus, no institutional review board approval was necessary.

Case 1

An 80-year-old man with type 2 diabetes and peripheral neuropathy had a history of multiple recurrent DFUs of the left plantar hallux interphalangeal joint. After more than 20 weeks with normal temperature readings (Figure 2A), the mat detected significant inflammation to the left hallux (Figure 2B). The patient was called and instructed to reduce ambulation by 50% of step-count. During outreach, he reported having not been seen in clinic for specialist foot care in more than 12 months. A follow-up call was conducted 1 week later, because the patient’s inflammation had not resolved from offloading. During this phone call, the patient reported callus on both feet and evidence of subcutaneous hemorrhage to the plantar left hallux, which caused a “hotspot” depicted in light yellow in the thermogram (Figure 2C). Prompted by these findings, the patient was seen in the clinic 1 week later, where a large callus was debrided and a non-infected DFU was discovered beneath the callus at the left hallux interphalangeal joint. The DFU measured 1.5 cm x 1.0 cm x 0.5 cm deep with red hemorrhagic drainage and macerated borders. A bony prominence at the right hallux also was noted. Five weeks after initial examination, the left hallux DFU was healed. As of this writing, surgical options were being considered to resolve the right foot bony prominence. 

Case 2

An 86-year-old man, with a history of peripheral neuropathy and Charcot neuroarthropathy but not diabetes, was found to have inflammation of the left medial forefoot about 2 weeks after a routine foot examination with no significant findings (Figure 3A). Although the patient is typically seen every 3 to 4 weeks for routine callus debridement, his next scheduled exam was in 6 weeks. Six days after being instructed to offload, the patient’s inflammation persisted, resulting in a follow-up call (Figure 3B). The patient’s caregiver completed a visual exam and noted callus coincident with the inflammation. Of note, the patient reported he had not received new accommodative shoes in more than 3 years. Given these findings, the patient’s exam was rescheduled, and he was seen in the clinic 2 days later. During that exam, the callus and tenderness at the left medial first metatarsophalangeal joint were noted. Upon debridement, a partial-thickness ulcer was revealed beneath the callus, with granular tissue and no signs of infection. At the same exam, the patient was prescribed new accommodative footwear. At exam 7 weeks later, the left foot ulcer remained partial thickness without signs of infection; however, a new ulcer to the right first metatarsophalangeal joint was noted and attributed to the patient’s new footwear. In a follow-up exam 3 weeks later, the left foot ulcer was completely healed without the use of advanced therapies over the entire episode. 

Case 3

A 62-year-old man with a history of right fifth metatarsal ray resection and right hallux amputation was contacted after detection of large inflammation to the right lateral forefoot. Upon outreach, the patient reported a large callus at the amputation site of the right foot. As a result of the outreach, the patient visited the clinic the following day, and the callus was debrided and a pinpoint DFU to the right hallux was noted. The patient has since elected prophylactic surgical intervention to prevent future complications to his right foot. 

Case 4

A 75-year-old man with diabetes and loss of protective sensation was noted to have large inflammation, manifesting as a 2.8°C temperature difference between the left and right feet at the fifth metatarsal head (Figure 4). Prompted by this monitoring, the patient was called and instructed to reduce ambulation by 50% step-count and increase diligence of daily foot checks. While giving subjective history, the patient reported a callus at a location consistent with the inflammation detected by the RTM mat. The next day, the patient noted drainage from the area and reported to the VHA emergency department, where he was triaged and referred to podiatry. Upon subsequent exam by podiatry, the callus was debrided and revealed a partial-thickness, granular DFU at the sub-fifth metatarsal head without signs of infection. During follow-up 2 weeks later, the DFU remained non-infected and partial thickness. After another 2 weeks, the DFU was healed.

The authors presented a case series of 4 veteran patients followed with an RTM mat, which extended a similar case series by Killeen and Walters.³⁵ Whereas their report³⁵ highlighted 3 cases with a mix of both prevention and early identification of DFUs with RTM, the present case reports focus exclusively on the benefits of early identification, which the authors believe may be underappreciated in the literature.

Multiple studies^21-23 have explored how wound healing is impacted by both the timeliness of initial treatment and severity of the wound at initial presentation. As several comorbid conditions (eg, visual impairment due to retinopathy and limited lower joint mobility) may prevent a patient from performing an efficacious self-exam in accordance with best clinical practices, the RTM mat may allow for improved treatment³⁸ and preventive care. In addition, because diabetic foot care by a specialist is typically only administered at intervals of every 8 to 12 weeks, identification of preulcerative and ulcerative lesions with RTM may allow targeted and timely treatment between routine exams.

These case studies highlighted the promise of early identification with an RTM mat for improved patient outcomes. In each case, the patient had a non-infected foot ulcer beneath the callus that healed quickly (within 4 weeks). Each patient healed without complication or use of advanced treatment modalities. In 2 of the cases (cases 1 and 3), the patients had not been seen for routine diabetic foot care for an extended period of time, and outreach prompted by the RTM mat re-established routine care. In those 2 cases, further prophylactic surgical interventions were pursued secondary to RTM findings, which have the potential to eliminate future complications due to structural foot deformities.

Given the staggering burden of diabetic foot complications in the VA,^33,39,40 telemedicine solutions (ie, RTM mat) have the potential to bring clinical practice into the home and reduce the burden of routine care on the clinics. Telemedicine may also improve veteran access to preventive foot care, which has been shown to be limited among high-risk veterans.⁴¹ In recognition of this, the VA National Prosthetic and Sensory Aids Service and the VA National Podiatry Program Office recently released a clinical guidance document on Temperature Monitoring Devices (TMD),⁴² governing appropriate use of RTM in veterans at risk for DFUs.

This is a small case series without a comparator, and thus cannot be used to make conclusions on relative effectiveness or accuracy of RTM in general or the RTM mat in particular. Although RTM is recommended by several practice guidelines, to date, the RTM mat has only been validated for its predictive accuracy. More research is needed to further quantify the benefits of the RTM mat for both prevention and early identification of DFUs and other inflammatory diabetic foot complications, such as Charcot arthropathy and foot infection. 

In addition, each of the 4 patients followed in this case series had largely intact feet, with only distal foot amputation history. Whereas previous approaches for RTM relied on contralateral comparison among plantar foot locations, recent advances in clinical understanding have enabled the study mat to monitor patients with only 1 foot available, due to proximal amputation or treatment of a wound to 1 limb. These patients are extremely high risk for the development of wounds and previously unable to benefit from RTM. Future research should explore the benefits of prevention and early detection of DFUs in patients with only 1 foot available for monitoring.⁴³

Results of this case series support the use of telemedicine 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,^33,35,38 suggesting the value of daily foot temperature monitoring for high-risk patients. Future research should focus on the impact of RTM for both prevention and early identification of DFUs for improved patient outcomes and reduction in resource utilization. 

Authors: Jaminelli L. Banks, DPM¹; Brian J. Petersen, MS, MBA²; Gary M. Rothenberg, DPM³; Annie S. Jong, DPM¹; and Jeffrey C. Page, DPM, DABFAS¹

Affiliations: ¹Phoenix VA Health Care System, Phoenix, AZ; ²Podimetrics, Inc, Somerville, MA; and ³University of Michigan Medical School, Ann Arbor, MI 

Correspondence: Brian J. Petersen, MS, MBA, Chief Scientist, Podimetrics, Inc, Clinical Affairs, 49 Day Street, Suite A, Somerville, MA 02144; brianjpetersen@gmail.com 

Disclosure: Mr. Petersen is an employee and shareholder of Podimetrics, Inc. Dr. Rothenberg is a consulting medical director for Podimetrics, Inc. All other authors disclose no financial conflict of interest.