System for Prediction of Recurrent DFU
differentiated from the maximum asymmetry of
scans from randomly sampled 2-month intervals from
participants who did not develop a DFU (Cohen’s
d = 0.79; 95% CI 0.76–0.81; P , 0.01). This nearly
constitutes a “large” effect size.
Table 2 presents the predictive accuracy of the
study device over a range of temperature asymmetry
thresholds that span sensitivity and specificity ranges
that we believe may find use in clinical practice.
At 2.22°C, the system correctly identified 97% of
observed DFU, with an average lead time of 37 days
with a false-positive rate of 57%. Extrapolating over a
year by assuming the true-positive and false-positive
rates are constant and equal to those observed during
the 34-week trial, we would expect; 3.1 notifications
per participant per year. Although only four discrete
temperature thresholds are presented, the values in
Table 2 can be interpolated to estimate performance
at different thresholds among those given.
Fig. 2 compares two typical and comparable
participants: one who did not develop a recurrent
DFU during the study (subject I, left panel), and one
who did (subject II, right panel). The top row of Fig.
2 presents the longitudinal temperature asymmetries
over time for both participants. The second row
presents two thermograms from each participant
collated by caption (A, B, C, and D) to the asymmetry
timeline history.
Subject I is a 61-year-old male participant with a
history of DFU at the left hallux (closed 40 weeks
prior to enrollment) and the right hallux status
postamputation (healed 42 weeks prior to enrollment).
At no time during study participation did he exceed
any of the temperature asymmetry thresholds in Table
2, and the participant remained ulcer free.
Subject II is a 59-year-old female participant with
a history of DFU at her right hallux and right
5th metatarsal head with no history of surgical
intervention. Her most recent DFU (right 5th
metatarsal head) healed 11 weeks prior to enrollment.
Temperature asymmetry exceeded 2.22°C at multiple
time periods during participation, and her right fifth
metatarsal head DFU subsequently recurred by week
10. On presentation, the wound was evaluated to be
University of Texas Diabetic Wound Classification
1A (superficial without ischemia or infection). The
inflammation associated with her emergent DFU is
clearly visible in Fig. 2, panel D.
Participant Disposition and Adherence
Of the 129 participants who had evaluable data, 14
(10.9%) withdrew consent prior to completion, 3
(2.3%) died, and 24 (18.6%) were lost to follow up.
The most common reasons for early withdrawal
were occurrence of a significant adverse event
not related to the device or participation in the
study (3.9%),“personal reasons” (2.3%), and poor
wireless signal strength (1.6%). In contrast, only one
participant withdrew consent because of difficulty
using the mat (0.8%).
Fig. 3 characterizes participant adherence to the
daily use of the device using both an ITT and a
per protocol approach. The top row (Fig. 3A and
B) represents adherence data from the study cohort
using an ITT approach; the bottom row (Fig. 3C and
D) represents adherence data from the study cohort
using the per-protocol analysis. The left columns
(Fig. 3A and C) display histograms stratifying the
participant population by the average number of uses
per week over the entire study duration. The right
columns (Fig. 3B and D) display the average uses per
participant per week of the study cohort over time.
Per ITT, 86% of the cohort used the system 3 days/
week or more. Mean adherence over the study period
was 5.0 days/week, with modest decay over time
Current Pedorthics | September/October 2019
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