Telemedical Monitoring of Plantar Temperature in Diabetic Patients at Risk of Foot Ulcers

Abstract

Background: The worldwide prevalence of diabetic foot ulcers (DFUs) among persons with diabetes is estimated at 6.3%, with an annual incidence of 9.1 to 26.1 million persons. The early detection of asymmetrical plantar temperature elevation, followed by reduction of weight-bearing on the affected foot, may be an effective mode of prevention.

Methods: Patients with diabetes and peripheral neuropathy (DFU risk groups 2/3) were monitored for plantar abnormalities with a telemedical system consisting of sole inserts with temperature sensors and photographic documentation. An open, prospective, randomized controlled trial was performed to determine whether this system prevented DFUs. The intervention and control groups were also trained in ulcer prevention and observed in follow-up at 6-month intervals for 24 months.

Results: 283 patients were recruited. In 85 137 observation days, DFUs arose in five patients in the control group (n = 143) and in no patient in the intervention group (n = 140). The primary outcome measure was the hazard ratio, which was calculated to be 0.015 (95% confidence interval [0; 19,717]; p = 0.25) after adjustment for age, sex, severity of neuropathy, and risk class. There were 239 alarms and 75 instructions to reduce weight-bearing on the foot. The subjects carried out the telemedical application on about 70% of the days of observation. Quality of life improved in both groups.

Conclusion: The tele-health system used in this trial is practical and enables the early detection of morbidity. Likely explanations for the unexpectedly low ulceration rate in this trial (and, in turn, for the lack of statistical significance) include the availability of a training program and regular follow-up examinations to patients in both arms of the trial, along with lower mobility levels due to the COVID pandemic.

Figure 1

Overview of the Smart Prevent Diabetic Feet telehealth system a) Patients in the intervention group were provided with sensor-equipped insoles and a cellphone app that exchanged data with the physicians in the hospital via the IQ-Trial study server. Plantar foot temperature recordings were recommended twice daily. The preset alarm algorithm automatically notified the study physician via the dashboard when temperature asymmetries (> 1.5 °C) between corresponding sensor sites lasted > 32 hours. Patients were instructed to perform foot inspections, document the foot status, and upload foot photographs. The physician decided, based on all available data, whether or not to recommend a 5-day period of foot offloading. On-site visits were arranged when temperature asymmetries persisted. b) Sensor-equipped insoles in sandals and start page of app. c) Insole sensor sites.

Figure 2

Flow diagram of Smart Prevent Diabetic Feet study A total of 283 patients with diabetes and peripheral polyneuropathy were enrolled in the study and randomized to the control or intervention group. Of these, 137 patients in the control group and 133 patients in the intervention group were evaluated after participating in training sessions on diabetic foot care. The patients in the intervention group additionally received the SPDF insole system for temperature measurement and instruction in use of the app. ITT, Intention to treat; SPDF, Smart Prevent Diabetic Feet

Figure 3

Study results and interpretation of the reasons for temperature alarms (a) Kaplan–Meier plot of plantar foot ulcer occurrence in the modified ITT population (n = 270) (b) Evaluation of alarms in the subgroups with minimal/mild or moderate/severe neuropathy within the intervention group (n = 123). Only events within the first 24 months of the study were included. (c) Overview of the alarms and the underlying reasons in the intervention group from the post-hoc analysis. (d) Alarm categories and duration for individual patients in the intervention group. Patients without alarms were not visualized (n = 52).

Figure 4

Temperature recordings and clinical findings of two patients with temperature abnormalities most likely due to transient ischemia. The temperature asymmetries correlated to clinical findings, infrared imaging, and ABI measurements. ABI, Ankle–brachial index; DFU, diabetic foot ulcer; MTH, metatarsal head; T, absolute temperature values measured by a sensor; ΔT: difference in absolute temperature between corresponding sensor sites, e.g., left MTH1 versus right MTH1.