The Potential Role of Sensors, Wearables and Telehealth in the Remote Management of Diabetes-Related Foot Disease
David G. Armstrong 6
Ulcer and wound Healing consortium (UHEAL), Queensland Research Centre for Peripheral Vascular Disease, College of Medicine and Dentistry, James Cook University, Townsville, Queensland 4811, Australia
The Department of Vascular and Endovascular Surgery, Townsville University Hospital, Townsville, Queensland 4814, Australia
School of Public Health and Social Work, Queensland University of Technology, Brisbane, Queensland 4000, Australia
Allied Health Research Collaborative, Metro North Hospital and Health Service, Brisbane, Queensland 4006, Australia
Interdisciplinary Consortium on Advanced Motion Performance (iCAMP), Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA
Southwestern Academic Limb Salvage Alliance (SALSA), Department of Surgery, Keck School of Medicine of University of Southern California, Los Angeles, CA 90089, USA
Author to whom correspondence should be addressed.
Sensors 2020, 20(16), 4527; https://doi.org/10.3390/s20164527
Received: 14 June 2020 / Revised: 29 July 2020 / Accepted: 12 August 2020 / Published: 13 August 2020
Diabetes-related foot disease (DFD), which includes foot ulcers, infection and gangrene, is a leading cause of the global disability burden. About half of people who develop DFD experience a recurrence within one year. Long-term medical management to reduce the risk of recurrence is therefore important to reduce the global DFD burden. This review describes research assessing the value of sensors, wearables and telehealth in preventing DFD. Sensors and wearables have been developed to monitor foot temperature, plantar pressures, glucose, blood pressure and lipids. The monitoring of these risk factors along with telehealth consultations has promise as a method for remotely managing people who are at risk of DFD. This approach can potentially avoid or reduce the need for face-to-face consultations. Home foot temperature monitoring, continuous glucose monitoring and telehealth consultations are the approaches for which the most highly developed and user-friendly technology has been developed. A number of clinical studies in people at risk of DFD have demonstrated benefits when using one of these remote monitoring methods. Further development and evidence are needed for some of the other approaches, such as home plantar pressure and footwear adherence monitoring. As yet, no composite remote management program incorporating remote monitoring and the management of all the key risk factors for DFD has been developed and implemented. Further research assessing the feasibility and value of combining these remote monitoring approaches as a holistic way of preventing DFD is needed.
Keywords: diabetic foot; remote-monitoring; sensors; prevention; telehealth; peripheral artery disease; diabetic peripheral neuropathy; remote patient monitoring diabetic foot ; remote-monitoring ; sensors ; prevention ; telehealth ; peripheral artery disease ; diabetic peripheral neuropathy ; remote patient monitoring
Diabetes-related foot disease (DFD), including foot ulcers, infection and gangrene, is one of the 10 leading causes of the global disability burden [ 1 ]. About 40% of people who develop DFD experience a recurrence within one year, and thus DFD represents a chronic disease; the focus of research into this should be on avoiding remission and preventing major consequences, such as amputation and death [ 2 ]. Key risk factors for DFD recurrence and complications in people at risk of DFD include high plantar pressures, abnormal gait, hyperglycaemia, hypertension and dyslipidemia [ 3 , 4 , 5 ]. Randomised controlled trials and meta-analyses show that foot disease is preventable by the control of these key reversible risk factors using interventions such as appropriate foot care, footwear and medical management [ 3 , 4 , 5 , 6 ]. A range of sensors and wearables have been developed or are currently under development for the remote monitoring of these key risk factors and this combined with telehealth management offers a way to remotely care for people at risk of DFD, as shown in Table 1 . The implementation of these approaches could also minimize the risk to patients and staff of exposure to the current global SARS-CoV-2 pandemic [ 7 , 8 ].
This review summarizes the potential application of remote monitoring systems using sensors and wearables to prevent DFD in the at-risk population, as shown in Figure 1 and Table 1 . The challenges of implementing remote DFD prevention and how sensors and wearables could be applied to better prevent DFD are discussed below.
2. Monitoring Foot Temperature
Most foot ulcers develop due to repetitive trauma on the feet of people with a loss of protective sensation, such as those with diabetic peripheral neuropathy (DPN) [ 2 ]. Recurrent trauma results in local inflammation, or a “hot spot”, which can be detected by an elevated temperature at the affected site [ 16 ]. This offers a means to identify people who are likely to develop foot ulcers for immediate foot care, such as the removal of calluses and modifications of footwear, to achieve better offloading to reduce this repetitive trauma and in turn the hot spot [ 2 ]. Most previous studies have used infra-red thermometers to measure foot temperature at multiple sites on both feet and compare identical sites on opposite feet [ 17 , 18 , 19 , 20 ]. Prior research suggests that a temperature difference between identical sites on opposite feet of >2.2 °C (equivalent to ~4 °F) on two consecutive days can accurately predict ulcer development [ 21 , 22 ]. It has recently been reported that the difference between the median of temperature at six key locations on one foot (the hallux, first, third and fifth metatarsal heads, the mid-foot and heel) and ambient temperature is also able to predict foot ulcer development with an excellent sensitivity, although with limited specificity [ 23 ]. This potentially allows people with a unilateral foot ulcer and those with prior unilateral major amputation to also be monitored for the hot spots that are predictive of impending ulcers.
Given its predictive value, regular foot temperature monitoring offers the opportunity to instigate urgent offloading and foot care, such as callus removal, to prevent an impending foot ulcer. Four randomised controlled trials have examined the efficacy of daily home foot temperature monitoring to signal the need for offloading in people at risk of diabetes-related foot ulcers [ 17 , 18 , 19 , 20 ]. Three of these trials [ 17 , 18 , 19 ], which were performed by the same team and included a total of 427 participants, reported a significant and substantial reduction in foot ulcer incidence in those allocated to home foot temperature monitoring. The other trial [ 20 ], performed by a different research group and including only 41 participants, reported no significant effect of home foot temperature monitoring and urgent offloading on foot ulcer incidence [ 20 ]. A larger randomised trial involving 304 participants is currently examining the cost-effectiveness and cost-utility of home foot temperature monitoring [ 9 ]. Recently, a further clinical trial reported on the efficacy of foot temperature monitoring performed at only monthly intervals at an out-patient clinic, rather than at home [ 24 ]. A thermal camera was employed to identify “hot spots” in order to advise on interventions, such as reductions in physical activity and improved offloading of the concerned area [ 24 ]. The trial included 110 people with a past history of a diabetes-related foot ulcers and reported no benefit of the intervention in preventing foot ulcers or improving health-related quality of life [ 24 ]. It is possible that these contrasting findings relate to the less-frequent monitoring of foot temperature performed, which may have missed an opportunity for the early identification of at-risk patients. These findings suggest the potential benefit of applying modern technology to regularly monitor foot temperature remotely in the participant’s home in contrast to less frequent monitoring in outpatient clinics.
The International Working Group on the Diabetic Foot (IWGDF) recently gave only a weak recommendation for the use of home foot temperature monitoring based on the moderate quality of evidence [ 25 ]. This likely reflects the small size of prior trials, limitations in the design of the previous trials and the practical difficulties of implementing home foot temperature monitoring. The previous trials testing home foot temperature monitoring [ 17 , 18 , 19 ] have excluded people with peripheral artery disease (PAD), which is an established risk factor for foot ulceration, thereby limiting the generalizability [ 20 , 21 , 22 ]. Both PAD and DPN have been reported to influence foot temperature [ 23 ]. In a recent thermal imaging study, participants with PAD had a significantly higher foot temperature than those that did not have PAD [ 26 , 27 ]. In contrast, previous studies have reported a positive correlation between foot temperature and ankle brachial pressure index, implying that people with PAD have a lower foot temperature [ 28 ]. This disparity might relate to whether people with severe PAD are studied or not. Furthermore, prior clinical experience and recent reports of infrared thermography show that foot temperature rises immediately following successful revascularization in correlation with the increase in the ankle brachial pressure index [ 29 ]. Given the established effect of leg ischemia on foot temperature and the exclusion of participants with this problem from prior trials [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ], the role of home foot temperature monitoring in people with PAD remains unclear. The ongoing trial of home temperature monitoring detailed above only excludes people with critical limb ischemia (defined as a systolic ankle blood pressure