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. 2019 May 23;14(1):37–45. doi: 10.1177/1932296819848769

Remote Temperature Monitoring in Patients With Visual Impairment Due to Diabetes Mellitus: A Proposed Improvement to Current Standard of Care for Prevention of Diabetic Foot Ulcers

Amanda L Killeen 1, Kara M Brock, James F Dancho 1, Jodi L Walters 1,✉
PMCID: PMC7189171  PMID: 31122064

Abstract

Background:

Two debilitating sequelae of diabetes are foot ulcerations and vision impairing conditions including retinopathy, open-angle glaucoma, and cataracts. Current standard of care recommends daily visual screening of feet. Despite willingness, many patients are impeded by visual impairment. We investigate whether once-daily remote temperature monitoring can improve self-screening for patients at risk for diabetic foot complications.

Methods:

We followed four male veterans with diabetes mellitus, peripheral neuropathy, impaired visual acuity, and at least one other diabetes-related visual impairment in a high-risk podiatry clinic. Patients received a telemedicine remote temperature monitoring mat and instructed on proper daily use. Each patient developed a “hotspot,” defined as a 1.75°C localized temperature difference between matched pedal locations, which resulted in telephone triage outreach.

Results:

In three cases, outreach resulted in a sooner appointment where patients were found to have a relevant outcome at the hotspot. Patients in cases 1-3 had University of Texas (UT) 1A ulcerations. The patient in case 4 had inflammation from trauma. All patients had refractive errors plus another vision impairing condition that potentially delayed identification of lesions. Patients in cases 1 and 2 have cataracts, patients in cases 2 and 3 have retinopathy, and patient in case 4 has glaucoma.

Conclusions:

As an adjunct to daily preventative diabetic self-care, once-daily remote temperature monitoring technology can augment self-screening to prompt necessary outreach and treatment and potentially prevent costly and debilitating diabetic foot complications. This case series serves as a pilot study for real-world application of thermometry, where further large-scale research is needed.

Keywords: diabetic foot ulcer, early detection, remote temperature monitoring, visual impairment

Foot ulcers are a common and devastating complication of diabetes. The global prevalence of diabetic foot ulcer (DFU) is 6.3%, with North America having the highest prevalence at 13%.1,2 In 2015, the International Diabetes Federation estimated that diabetic foot ulcers develop in 9.1-26.1 million people worldwide annually.2,3

The development of DFU is associated with significant increased morbidity and mortality. Patients with a DFU are three times more likely to die at any time compared to patients with diabetes without a foot ulcer.4 A retrospective study of Veterans Health Administration (VHA) data found the one-year, two-year, and five-year survival rates for veterans who had suffered a DFU to be 81%, 69% and 29%, respectively.5 Another retrospective study in veterans found that diabetes-related lower extremity amputations are common and expensive. These investigators reported that the VHA performed 3403 diabetes-related lower extremity amputations (LEA), 2.7 per 1000 veterans with diabetes, in fiscal year 2010, far surpassing the rate of traumatic LEA in veterans. The average inpatient cost associated with each of these diabetes-related LEA procedures (excluding LEA-attributable costs postdischarge) exceeded $60 000 in 2010.6

Under current standard of care recommendations, patients with diabetes are educated and instructed by doctors, nurses, or diabetes educators to perform a daily visual foot exam to look for preulcerative lesions, discoloration, and swelling of their feet.7-10 Education on self-care is imperative because recent research indicates that half of DFUs can be prevented through effective education and 50-70% of lower limb amputations are the result of a DFU.11

Unfortunately, other vision impairing sequelae of diabetes, such as retinopathy, open-angle glaucoma, and cataracts prevent many patients from adequately completing daily self-exams. Advanced diabetes mellitus has been associated with several morphological and functional changes in optical anatomy. Developing over several years, adults with diabetes experience an increase in lens thickness and distortion in the curvature of the lens surface.12 Hyperglycemia has been associated with myopic refraction, while hypoglycemia has been suggested to lead to the development of hyperopia, or farsightedness.12,13

Retinopathy affects about a third of all patients with diabetes,14 causes loss of visual acuity,15-19 and is an independent risk factor for diabetic foot ulcers (DFU) and amputation.20-27 In addition to retinopathy, diabetes can exacerbate open-angle glaucoma,28,29 cataracts,30-33 and macular edema.14,34 Due to these increased risks of visual impairment, current guidelines from the American Diabetes Association (ADA) recommend annual eye examinations. Despite patient education and awareness of these risks, one-third of these patients fail to complete annual vision screening.35,36

Despite patients’ comprehension and willingness to adhere to daily foot exam, vision impairing comorbidities prevent them from performing one adequately. Therefore, it is necessary to develop alternative screening methods for prevention of DFUs. One such modality is thermometry, the use of skin temperature monitoring to detect the inflammation due to repetitive microtrauma or acute injury preceding to skin breakdown.37,38 Thermometry is evidence based and supported by three randomized controlled trials.38-40 A recent multicenter cohort study of 132 patients utilizing thermometric foot mat found that the system identified 97% of observed DFUs with an average lead time of 37 days.37 However, the current literature is lacking on the implementation of this technology with appropriate treatment interventions in a real-world setting.

This case series illustrates the implementation of a remote temperature monitoring (RTM) mat (Podimetrics RTM System; Podimetrics, Inc, Somerville, MA) to identify ulcerative and preulcerative lesions to prompt noninvasive intervention in patients with diabetes-related visual impairment who are unable to perform effective daily visual foot exams.37,41 This easy-to-use smart floor mat contains more than 2000 thermistor sensors. The patient is instructed to stand stationary on the mat once daily for about 20 seconds, after which the data are then wirelessly transmitted to a secure server and automatically analyzed for signs of inflammation.37

Methods

This case series was conducted at a single center (Southern Arizona Veterans Affairs Health Care System). Four male veteran patients were chosen via retrospective chart analysis from the authors’ high-risk podiatry clinic. Patients had previously been screened and prescribed a thermometric smart mat for daily use as an adjunct to standard preventative diabetic foot care. To qualify for the mat at the high-risk podiatry clinic, the patients must have at least three of the following: peripheral neuropathy (per Semmes-Weinstein monofilament testing), peripheral vascular disease, foot deformity, history of foot ulceration, or history of LEA. Due to the small sample size, this study was not required to obtain IRB approval per VA guidelines.42

Patients were asked to stand barefoot on the RTM mat at home for a once-daily foot “scan” at approximately the same time each day. Mat sensors cover the entire mat surface so patients with poor vision do not need precise foot placement37 (Figure 1A). Deidentified thermometric scans are transmitted securely to a remote server. Clinical staff can access foot temperature maps, called “thermograms,” derived from the scans through a secure online physician portal (Figure 1B). These data are used for triage by health providers and to counsel patients. They are recorded in patient’s medical records via clinician note. All data collected, used, and presented herein have been deidentified in accordance with best practices and federal and local regulations.42

Figure 1A.

Figure 1A.

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The smart telemedicine remote temperature monitoring mat. Copyright 2018. Wounds.41

Figure 1B.

Figure 1B.

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Secure clinician portal to analyze thermograms.

The data collected by the mat are automatically analyzed for temperature differences, or “asymmetry,” between the left and right feet at six locations: heel; arch; first, third, fifth metatarsal heads; and hallux, using the approach most common in the literature.38-40 Although a threshold of 2.2 degrees of asymmetry has been most commonly described in the literature, the decision to utilize a 1.75 degree threshold was made in an effort to optimize sensitivity.37 A patient with temperature asymmetry exceeding 1.75°C over two or more consecutive uses at the same location triggers a deidentified action-oriented notification and inflammation report from the device manufacturer to the clinical staff. This alert identifies the laterality, anatomic location, and degrees of asymmetry detected. Each asymmetry triggers a phone call for triage. The outreach is done by a designated clinician who contacts the patient and asks for subjective information relating to erythema, edema, contusions, pain, and skin breakdown. If possible, the clinician will guide a caregiver through a visual exam. A protocol has been developed to reduce walking for the next several days, continue offloading footwear, and, if necessary, schedule a sooner appointment date.

This case series was conducted in accordance with VHA guidance on case series. Thermometry is recognized as a component of standard care43-45 and the device is cleared by the US Food and Drug Administration (K150557) for this intended use. This case series does not constitute research due to small size, lack of testable hypothesis, and practice in accordance with standard of care. Thus, it does not require approval by an institutional review board.42

Results

Case 1 is a 71-year-old male with type 2 diabetes mellitus (HbA1c = 5.6%), neuropathy, B12 deficiency, neurocognitive disorder, hypertension, Charcot neuroarthropathy of the right foot and ankle, hyperopia with astigmatism and presbyopia, glaucoma with borderline ocular hypertension of both eyes, and mild cataract of both eyes.

The patient received telephone outreach due to three consecutive scans with peak asymmetry of 3.1°C localized to the right hallux (Figure 2). The patient performed a visual exam while on the phone and reported no redness, no swelling, no calluses, and no open wounds to the area of clinical concern. He denied trauma, increased activity, or any other changes and elected to keep his routine appointment in two months rather than be seen sooner.

Figure 2.

Figure 2.

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Localized inflammation hotspot of 3.1°C detected on the right hallux. A superficial plantar hallux ulcer was found.

The following day, the patient called the podiatry department to report that his wife performed a visual exam of the patient’s feet and found an ulcer to the plantar right hallux. He was seen the same day for debridement of a University of Texas Diabetic Wound Classification46 UT1A ulcer measuring 0.7 x 0.7 cm x superficial. With proper education of the patient and his wife, proper dressing changes, and offloading, the ulcer healed without any advanced modality in 19 days.

Case 2 is a 68-year-old male with type 2 diabetes mellitus (HbA1c = 6.5%), neuropathy, lumbar post-laminectomy syndrome with radiculitis, degenerative lumbar stenosis, myopia with astigmatism and presbyopia, nonproliferative retinopathy of the left eye, and cataracts of both eyes.

The patient received telephone outreach for an asymmetry of 2.7°C diffusely to the right forefoot (Figure 3). On the phone, the patient reported no knowledge of trauma, change of footwear, or ulceration to the area. He kept his previously scheduled appointment and was seen nine days later. Upon exam, a UT1A ulcer measuring 0.8 x 0.8 x 0.3 cm was discovered after debriding hyperkeratosis of his right plantar 2nd metatarsal head. The patient was given proper toe offloading in conjunction with his diabetic shoes, and the ulcer healed in 33 days.

Figure 3.

Figure 3.

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Diffuse forefoot hotspot of 2.7°C detected on the right forefoot. Superficial ulcer found plantar to second metatarsal.

Case 3 is a 68-year-old male with type 2 diabetes mellitus (HbA1c = 7.1%), neuropathy, diabetic nephropathy, hypertension, hyperlipidemia, myopia with astigmatism and presbyopia, and proliferative diabetic retinopathy.

The patient received telephone outreach for an asymmetry of 3.7°C to the left hallux (Figure 4). Upon outreach, the patient denied trauma and reported he “didn’t think there was an ulcer” but had pain in the left hallux. The patient has loss of protective sensation.

Figure 4.

Figure 4.

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Hotspot of 3.7°C detected on the left hallux. A fissure in the hallux sulcus was found.

The following day the patient was seen in clinic. Upon exam, there was a UT1A fissure measuring 1.0 x 1.0 x 0.1 cm in the sulcus of the left plantar hallux. It was debrided and dressed appropriately. His offloading orthotic in the shoe was found to be appropriate and he was given dressing supplies. The fissure healed in 5 days.

Case 4 is a 65-year-old male with type 2 diabetes mellitus (HbA1c = 7.6%), neuropathy, paresthesias, adrenal tumor, depression, hypertension, and glaucoma of the left eye due to glaucomatocyclitic crisis.

The patient received telephone outreach due to an asymmetry >3°C between both halluces. The right hallux had previously been warmer, then became cold (approximately ambient temperature) in the thermograms (Figure 5). The patient reported no redness, no swelling, no ulcers in the area of clinical concern upon outreach triggered by the mat. The patient reported he may have had a bandage on his toes, though he didn’t remember which while standing on the mat. He then reported a subungual hematoma of the right hallux two weeks prior likely due to trauma that was resolving uneventfully. He went on to heal uneventfully.

Figure 5.

Figure 5.

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Asymmetry between halluces of 3°C. The right hallux was initially warmer, then cooled to ambient temperature. Inflammation due to trauma.

Discussion

The economic and time cost of a 3- to 5-minute outreach phone call which triggers a 15-minute clinic visit for debridement, is inexpensive compared to a DFU, the aggregate costs of which exceeds $1.5 billion annually and continues to increase.47-49 For high risk cohorts such as those who have recently healed from a wound, incidence has been consistently shown to be between 30% and 40% in the year following epithelialization.2 Given the large treatment effect documented across three RCT in the 2000s, which averaged 70%,38-40 the number needed to treat may be as low as four during this critical period of remission. Lifetime incidence of foot ulcers among patients with diabetes has been estimated at 25%,50 which implies a lifetime number needed to treat of six. Thus, the economics of prevention, especially among high risk cohorts, is compelling: A recent meta-analysis reported that the average cost to a public payor in the year following a foot ulcer exceeds $44 000.51

Severity of ulcers determines the average per-episode cost, which ranges from $1900 for Wagner grade I52 to over $27 000 for Wagner grade IV or V with inpatient care accounting for greater than 70% of dollars spent.53,54 Early intervention can shorten the DFU course and also decrease major resource utilization in emergency department visits and hospital admissions. Because as many as 50% of patients who heal from a DFU experience recurrence within 2 years, wound healing is impacted by both the timeliness of initial intervention and the severity of the wound.37,55-58 The remote temperature monitoring mat alerted clinical staff to areas of concern that were triaged appropriately and treated quickly. The ulcers in cases 1-3 were of low severity and uninfected (UT1A) at initial presentation. None of the patients in these cases had a DFU-related hospital admission or emergency room visit in the time following their hotspots—59 weeks for case 1, 87 weeks for case 2, 87 weeks for case 3, and 74 weeks for case 3.

In case 1, the patient performed a visual exam to the best of his ability but failed to see an ulcer. He has hyperopia with presbyopia, glaucoma, and cataracts. Hyperglycemia causes transient refractive changes in patients with diabetes. After episodes of hyperglycemia are resolved, patients’ corneal typography trends toward hyperopia, for which this patient wears corrective lenses.12 Patients with diabetes can perform adequately on Snellen eye exams, which test for differentiation between shape sizes, but perform poorly in low-contrast testing.59 In a self visual exam where examining pedal skin color and appearance are paramount, this impacts the effectiveness the exam being performed. The patient’s systemic hypertension may have caused damage to the microvasculature of the retina likely explaining the etiology of his primary open-angle glaucoma.28-29,60-61

In case 2, the patient has myopia with astigmatism as well as presbyopia, cataracts of both eyes, and nonproliferative retinopathy of the left eye. For patients who have retinopathy combined with myopia and presbyopia, focusing on objects like the foot can be a challenge. Myopia is an anatomic refractive error which causes incoming light to be focused anterior to the retina, while presbyopia is an age-related refractive error that causes light to be focused posterior to the retina.62 This variation in focus could explain why the patient in case 2 could not see the ulceration on his foot. There is evidence that myopic eyes may be less likely to have retinopathy due to morphology, but the addition of presbyopia exacerbates the visual impairment.63

The patient in case 3 has myopia and presbyopia with proliferative retinopathy in both eyes. Worldwide, diabetic retinopathy affects one third of patients with diabetes.14 Data show that development of cataracts begins with impaired fasting glucose and progresses earlier and occurs 2-5 times more often in patients with diabetes.30,32

The patient in case 4 has hypertension in conjunction with glaucomatocyclitic crises which are attacks of increased intraocular pressure thought to be due to mononuclear cell infiltration of trabecular interspaces.64 The transient nature of this pathology may mean self-visual exams are impaired even when the patient experiences no symptoms.

Previous literature outlined using thermometry to prompt reduced ambulation for patients with asymmetry between contralateral locations on the feet exceeding 2.2°C over two consecutive days.38-40 At the 2.2°C threshold, the RTM mat was shown to predict 97% of nonacute plantar DFUs with 37 days lead time and a specificity of 43%.37 A previously unpublished analysis on the original dataset suggests that at the 1.75°C threshold, the RTM mat was able to predict 100% of nonacute plantar DFUs with 42 days lead time and specificity of 25%.65 During the initial phase of RTM use, the decision was made to lower the facility threshold from 2.2°C to 1.75°C.41 In a noninterventional setting, this false positive rate may seem quite high, but the specificity in a research setting considered only inflammation with incident DFU as a true positive finding. In reality, pedal inflammation and diabetic foot complications is multifactorial and can stem from preulcerative lesions like callus that increase plantar pressures by up to 30% and result in inflammation that would have been reported as a false positive in the previous research on the mat.66 Repetitive microtrauma can cause increased local pedal pressures, which leads to subcutaneous hemorrhage and ultimately tissue breakdown.67-69 Debridement of these preulcerative lesions is a vital modality in prevention of DFU as it can lower peak plantar pressures more than reduced ambulation, accommodative footwear, and tendo-Achilles lengthening.70,71 In patients with diabetes-related visual impairment and neuropathy, identification of hyperkeratotic or devitalized tissue is delayed, and as illustrated in the preceding cases, was recognized by the RTM prior to their regularly scheduled diabetic care clinic visits.72

Loss of visual acuity can be a complication of pathologic changes to ocular anatomy secondary to increased systemic inflammation in diabetes. For example, macular edema is the deposition of proteinaceous fluid around the macula from leaky microvasculature, causing disruption to the central field of vision. The mechanism is proposed to be hyperglycemia-independent and instead be due to advanced glycation end products (AGE) that affect both the micro- and macrovascular systems.73-79 Systemic inflammation could also account for bilateral pedal abnormalities that are not recognized by conventional asymmetry-based remote temperature monitoring approaches.

These cases highlight the promise of early detection in patients with diabetes-related visual impairment for improved outcomes for those at high risk for amputation and ulceration.

Limitations

The authors acknowledge this is a small case series limited by its size and lack of comparator. Although thermometry is recommended by several practice guidelines68,80,81 and outcomes trials38-40 the RTM mat is not yet widely available outside the VA system due to lack of insurance reimbursement. More research with a larger cohort is warranted to explore the benefit of once-daily remote temperature monitoring to augment daily self-exam in patients at-risk for DFUs.

Conclusion

Many patients with advanced diabetes mellitus suffer from visual impairment in the form of retinopathy, glaucoma, cataract, and macular edema as a progression of their disease and are therefore not able to adequately perform visual screening exams of their feet, which is a recommended part of preventive practice. When used as an adjunct to daily preventative diabetic self-care, remote temperature monitoring can be a technological solution for improved self-screening to prompt appropriate outreach and treatment, and potentially prevent ulceration for those at high risk of complication.

Acknowledgments

The Southern Arizona VA provided support and facilities.

Footnotes

Authors’ Note: Amanda L. Killeen is a third year resident and Kara M. Brock is a second year resident.

Abbreviations: ADA, American Diabetes Association; AGE, advanced glycation end products; DFU, diabetic foot ulcers; HbA1c, hemoglobin A1c; LEA, lower extremity amputations; RTM, remote temperature monitoring; UT, University of Texas; VHA, Veterans Health Administration.

Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD: Amanda L. Killeen Inline graphic https://orcid.org/0000-0002-8461-9139

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