By Keith Loria
The concept of foot temperature monitoring to identify areas of increased risk of ulceration in patients with diabetes is promising, but new research from the Netherlands suggests clinical use of the technology will require more than a single temperature assessment.
In 20 patients with diabetes and peripheral neuropathy recruited from a multidisciplinary Dutch foot clinic, investigators found that very few of the “warning signals” identified using a single assessment could be confirmed on subsequent days during the six-day study period.
“If you want to use foot temperature measurements in clinical practice to prevent foot ulceration then you have to do more than single measurements,” said Jaap van Netten, PhD, coauthor of the study, senior researcher at Academic Medical Centre Amsterdam, and adjunct associate professor at Queensland University of Technology in Brisbane, Australia. “If you do want to use them, make sure they are done on consecutive days to confirm any abnormal findings before they think it might be a foot ulcer.”
The study, which was epublished in October by the International Wound Journal, specifically focused on the concept of a 2.2°C difference between left and right feet for a particular plantar location; earlier studies have proposed that temperature differences above this threshold are indicative of an area at high risk for ulceration.
“The most important message is that in the prevention of diabetic foot ulceration, a single measurement of the >2.2°C left-to-right foot temperature difference threshold for impending ulceration is not valid,” study coauthor Anke M. Wijlens, MSc, a researcher in the department of internal medicine at Radboud University Medical Center in Nijmegen, the Netherlands, wrote in an email. “The validity improves to acceptable levels with subsequent confirmation of the >2.2°C left-to-right foot temperature difference the following day and further improves with individual correction.”
In the study, patients monitored their skin temperature with an infrared thermometer—a simple device chosen to facilitate compliance—at the plantar hallux, metatarsal heads, midfoot, and heel four times a day for six consecutive days. The study population included some patients with a foot deformity or peripheral arterial disease, but none had history of foot ulceration or amputation.
“We chose this group because it’s a rather homogenous population, whereas if you look at people with a previous foot ulcer, you tend to get much greater variation,” van Netten said. “We also don’t really know what a previous foot ulcer does temperature-wise.”
At single locations, a left-to-right temperature difference greater than 2.2°C was found 245 times (8.5% of measurements). Confirmation of these above-threshold readings on the following day was found seven times (.3%). Corrected for individual left-to-right mean foot temperature differences at baseline, this reduced to four (.2%).
None of the participants developed an ulcer during the short study period, but the researchers concluded a single-assessment approach was far more likely to lead in false-
positive results than if a temperature difference was confirmed in multiple assessments.
Interestingly, the participants were told to contact the researchers after any increase in temperature above the threshold was detected, yet none did.
“We struggled with this, because we thought we gave very clear instructions to the patients, but none of them called or contacted us in any way,” van Netten said. “It could be because they were all relative low-risk with no previous history of ulceration, so they felt there was nothing wrong. If you do implement repeated temperature measurements, you need to be really actively involved to make sure that patients are advised to keep doing it.”
David Armstrong, DPM, MD, PhD, professor of surgery and director of the Southwestern Academic Limb Salvage Alliance at Keck School of Medicine at the University of Southern California in Los Angeles, agrees with the study’s findings.
“They are correct—no single measurement is in and of itself accurate,” Armstrong said. “It is a collective series of data showing inflammation or change that is predictive.”
Wijlens AM, Holloway S, Bus SA, van Netten JJ. An explorative study on the validity of various definitions of a 2.2°C temperature threshold as warning signal for impending diabetic foot ulceration. Int Wound J. 2017 Oct 9. [Epub ahead of print]