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.
