Impact of Remote Foot Temperature Monitoring

Skin temperature monitoring as a useful tool to detect tissue at risk for breakdown and ulceration first emerged in the 1970s and has been examined by several investigators. For neuropathic wounds (excluding acute injury) the hypothesized mechanism is believed to be repetitive stress and micro-trauma leading to enzymatic autolysis of tissue, inflammation, and a resulting measurable increase in local skin temperature.

In 1997, a paper was published examining 143 consecutive patients presenting to the University of Texas' High Risk Diabetic Foot Clinic. They hypothesized that individuals with acute pathology would show an increase in skin temperature when comparing the affected foot to the contralateral unaffected foot. Mean delta-temperatures for neuropathic ulcers and Charcot arthropathy were found to be 5.6°F (n=44, p<0.0001) and 8.3°F (n=21, p<0.0001), respectively. No statistical difference was found in neuropathic participants without acute pathology (n=78).

In a project funded by the National Institute of Health, the same investigators conducted a series of studies, published between 2004 and 2007, examining the impact of self-assessed dermal thermometry in high-risk diabetic patients In the first randomized controlled trial in 2004, 85 patients were assigned to one of two groups, Usual Therapy or Enhanced Therapy.

Participants were eligible if they had either a history of foot ulceration or lower extremity amputation, or if they had moderate to severe peripheral sensory neuropathy with a foot deformity. Both groups received therapeutic footwear, diabetic education, and regular foot evaluation by a podiatrist. Enhanced Therapy participants additionally received a hand-held dermal thermometer to self-record dermal temperatures at six sites on each foot, twice per day. If a delta-temperature between any two corresponding sites was found to be greater than 4 F, participants were instructed to reduce activity and contact the study nurse. After six months of follow-up, Enhanced Therapy participants experienced significantly fewer foot ulcerations and Charcot fractures (2% vs. 20%, p=0.01) than the Usual Therapy group. The study was blinded to physician only. A limitation of the study was the difficulty in determining whether the Enhanced Therapy group received greater attention by the care team, and therefore better monitoring and therapy.

In their second randomized controlled trial conducted in 2007, 173 participants were enrolled between the Texas A\&M University Health Science Center and the Rosalind Franklin University of Medicine and Science. Participants were eligible if they were diabetic and had a history of previous foot ulcer, and were assigned to one of three groups: Standardized Therapy, Structured Foot Exam, and Enhanced Therapy. All three groups received standard of care (therapeutic footwear, diabetic foot education, and regular foot evaluation by a podiatrist) and were instructed to contact the study nurse if they noticed any abnormalities during their daily foot inspection. The Structured Foot Exam group, in addition to standard training, were instructed to conduct a structured foot inspection twice daily with the assistance of a mirror and record any noted changes in color, swelling or warmth in a detailed log book. The Enhanced Therapy group, in addition to standard training, were trained to use a hand-held dermal thermometer to record daily foot temperatures at the six locations on each foot, noting any delta-temperatures between feet. Should a difference between corresponding sites be found greater than 4 degF for two consecutive days, participants were instructed to contact the study nurse and decrease activity until temperatures normalized. After 15 months of follow-up, Enhanced Therapy participants had fewer foot ulcers than Standard Therapy participants and Structured Foot Examination participants (Enhanced Therapy 8.5% vs. Standard Therapy 29.3%, p=0.0046; and Enhanced Therapy 8.5% vs. Structured Foot Examination 30.4%, p=0.0029). No difference was found between Standard Therapy and Structured Foot Exam groups. The study was physician blinded as before.

In the third RCT, 225 patients from the Southern Arizona VA Healthcare System (Tucson, AZ) were randomized between the Standard Therapy Group and the Dermal Thermometry Group. Eligible participants had either a history of foot ulcer or partial foot amputation or a history of neuropathy and structural foot deformity or limited joint mobility. Participants were followed for 18 months, blinded to the physician. Both groups received standard of care and performed daily structured foot self-examinations. The Dermal Thermometry Group additionally received a hand-held dermal thermometer to assess six plantar foot sites twice per day. Dermal Thermometry Group patients were instructed to contact the study nurse if delta-temperature between corresponding locations on the feet exceeded 4 F for two consecutive days and decrease activity until the temperature asymmetry normalized. Dermal Thermometry patients were 61% less likely to ulcerate: 12.2% ulceration in the Standard Therapy Group vs. 4.7% ulceration in the Dermal Thermometry Group (O.R. 3.0, 95% CI 1.0-8.5, p=0.038). Further, proportional hazards regression analysis adjusting for elevated foot ulcer classification (International Working Group Risk Factor 3), age, and minority status suggested that temperature-guided avoidance therapy was associated with a significantly longer time to ulceration (p = 0.04).

One significant challenge to temperature guided avoidance therapy owe to the manual process of collecting and recording temperatures. With current technologies the following steps must be taken each day: temperatures measurements are acquired at six different locations on each foot, the values are recorded in an organized fashion in a log book, and the history of values are interpreted for trends in temperature difference between each foot. This process places a significant burden on the patient. Further, as day-to-day usage of the technology cannot be tracked, managing adherence becomes challenging.

The purpose of this study is to demonstrate the feasibility of temperature-guided avoidance therapy via the a foot temperature monitoring telemedicine mat (Podimetrics SmartMat; Podimetrics Inc., Somerville MA) on preventing the occurrence of diabetic foot ulcers and associated resource utilization in patients with a recently healed diabetic foot ulcer.