Digital Thermometry: Can It Have An Impact?
Preventing foot ulceration and re-ulceration in high-risk patients with diabetes is a challenge. Clinical outcomes are much better when high-risk patients receive proper foot care, education and protective shoes. There is a growing body of work which demonstrates that programs aimed at treatment and prevention significantly reduce ulcers, amputations and hospital admission.1-4 However, even at “centers of excellence for the diabetic foot,” the rate of ulcer recurrence is still very high.
In a randomized clinical trial, Uccioli reported a 28 percent re-ulceration rate in one year in patients with diabetes who had a history of foot ulceration (see “A Closer Look At The Studies On Shoes And Insoles For People With Diabetes” on page 54).5 The only other randomized clinical trial to study therapeutic shoes evaluated a mix of low and high-risk patients and determined that patients received no benefit from footwear. The poor results in this study were probably due to the fact that 42 percent of the study population did not have sensory neuropathy and were unlikely to have an ulcer or benefit from prevention.
The use of temperature to evaluate the diabetic foot is not new. Until recently, however, there have only been a handful of descriptive studies. Previous works have described the use of temperature to evaluate neuropathic ulcers, Charcot arthropathy and the effectiveness of bisphosphonates and antibiotics. The rationale to using temperature involves the search for a quantifiable measurement of tissue injury and tissue recovery in the insensate foot.
Several authors have suggested that skin temperature monitoring may be a valuable tool to detect sites “at risk” of ulceration in patients with neuropathy over the past 40 years. As early as 1971, Goller and colleagues identified an association between increased local foot temperatures and localized pressure leading to tissue injury.6 In 1972, Sandrow and colleagues used thermometry to diagnose Charcot fractures in patients with diabetes and sensory neuropathy.7 Subsequently, Stess and Clark described the use of infrared thermography to assess skin temperatures in diabetic controls with no foot pathology, diabetic patients with Charcot arthropathy, diabetic patients with neuropathic foot ulcerations, patients with neuropathy due to leprosy and healthy controls. They found that neuropathic foot ulcers frequently had increased skin temperatures surrounding a cooler, central necrotic area.8,9
Benbow and colleagues used thermography to evaluate a cohort of patients with diabetes.10 They felt that clinicians could use temperature patterns from thermographic scans to screen and identify high-risk patients. They prospectively evaluated 50 patients with diabetes and sensory neuropathy for three to four years. Six patients developed foot wounds during the study period. These patients had significantly higher foot temperatures at baseline than patients who did not ulcerate.
What Some Studies Have Revealed About Temperature Monitoring
Temperature monitoring has also been advocated as a clinical tool to monitor compliance with offloading as well as the treatment of Charcot fractures in people with diabetic neuropathy. Armstrong used an infrared temperature device to evaluate a cohort of diabetic patients with neuropathic fractures.12 Armstrong tracked a cohort of patients treated for Charcot foot fractures with serial total contact casting and as they progressed to less restrictive offloading with fracture boots and therapeutic shoes and insoles. Since this patient population had painless fractures, researchers could not use the traditional clinical examination to determine if there was pain at the fracture site. Armstrong immobilized patients until their temperatures were the same as the contralateral extremity before progressing them to the next stage of weightbearing.
Armstrong also described the use of temperature monitoring in a cohort of subjects with foot ulcers.13 He evaluated the difference in temperature at the site of neuropathic foot ulcerations and compared temperatures with the corresponding site on the unaffected foot. Foot temperatures at the ulcer site were significantly higher than the opposite foot at the time of initial treatment. Temperatures decreased as the surface area of the wound decreased until they were eventually less than the “control sites.”
Recognizing The Challenges With Self Assessment Of The Foot
There has been little innovation in preventative care for high-risk patients with diabetes. While we have made considerable progress in demonstrating the impact of proactive foot care to heal foot wounds in order to avoid amputation and reduce hospitalizations, there has not been much headway in advancing prevention. Perhaps the most exciting recent development is the use of temperature assessment as a home evaluation and monitoring tool for high-risk patients.
Before a wound develops on the sole of the foot, the area is usually exposed to repetitive injury and there is a localized inflammatory response. Inflammation is one of the earliest signs of tissue injury and ulceration. However, the classic signs of inflammation (redness, pain, swelling, loss of function and heat) are difficult to quantify by patients and healthcare providers. In the neuropathic extremity, pain is obscured by neuropathy. Therefore, the elements of pain and the loss of function are not factors when the insensate foot is injured. Likewise, swelling and redness are very difficult to grade objectively, to communicate to other clinicians and to document. Subtle changes in swelling or redness are impossible to monitor over time.
Temperature changes seem to be the easiest of the cardinal signs of inflammation to identify and record. One can easily identify and record subtle changes. A handheld infrared thermometer can quickly identify local areas of inflammation that would not be recognized with the “traditional” methods of visual inspection and physical examination.
Can A Handheld Temperature Assessment Tool Have A Preventive Impact?
There have been three randomized clinical trials to determine if patients can effectively use a handheld temperature assessment tool to avoid foot ulcers.13-15 All three studies have demonstrated a three- to 10-fold reduction in incident foot ulcers in high risk patients with a history of a foot ulcer or with sensory neuropathy and foot deformity. These studies used a similar basis for “standard prevention therapy.” Patients in the control group received therapeutic shoes and insoles, and a standardized diabetic foot education program.
Lavery and co-workers evaluated the effectiveness of the TempTouch (Xilas Medical), a handheld infrared temperature monitoring device, in a cohort of 180 high-risk diabetic patients with a history of foot ulceration or partial foot amputation.16
There were three treatment arms in the study. The standard therapy group received therapeutic shoes and insoles, patient education and regular foot evaluations by a podiatrist every 10 to 12 weeks. For the “Structured Foot Evaluation Group,” researchers had patients perform a systematic foot evaluation twice a day to identify local signs of tissue injury, redness, discoloration, swelling and local warmth, and record their findings in a log book in addition to receiving standard therapy. Patients also used a hand mirror to visualize the bottom of their feet. The temperature monitoring therapy group received standard therapy plus the addition of the TempTouch. They measured temperatures on six sites on the sole of each foot once a day. If temperatures were elevated by greater than 4ºF in comparison to the same site on the contralateral foot, patients had to reduce their activity until the temperatures normalized.
The incidence of foot ulceration during the 15-month evaluation period was essentially identical in the standard therapy (29.3 percent) and structure foot evaluation (30.4 percent) treatment arms. However, there was more than a fourfold decrease in the risk of developing foot ulceration in patients in the temperature monitoring therapy group in comparison to the standard therapy group and the structured foot evaluation group. In both control arms, the incidence of foot ulceration was about 30 percent. This is similar to the findings of Uciolli and Dargis when they provided “standard therapy” to high-risk patients with diabetes.5,17
Temperature monitoring in the lower extremity is a very new area and it presently does not seem to lend itself to the kind of absolutes we are accustomed to relying on when we evaluate core body temperature. Sensory neuropathy, autonomic neuropathy and peripheral vascular disease (PVD) can dramatically effect skin perfusion in the lower extremity. Therefore, temperatures can vary widely across similar groups. In the past, several studies have used the contralateral extremity as a “control,” assuming that the negative or positive effects of PVD and neuropathy would be systemic and symmetrical in the same individual. The three randomized clinical trials that focus on ulcer prevention ask patients to compare temperatures on the contralateral extremity. These studies use a 4ºF (2.2ºC) difference to identify an area that was inflamed and prone to ulceration.
Armstrong and colleagues reported the results of a randomized, blinded 18-month clinical trial at the Tucson Veterans Administration Hospital.14 Armstrong’s group evaluated 225 patients with diabetes at high risk for ulceration (neuropathy and deformity or previous history of ulceration). Half of the patients received standard therapy and half were in a temperature monitoring treatment group. Both groups received therapeutic footwear, diabetic foot education and regular foot care. All patients learned how to perform a systematic foot evaluation, and they were asked to inspect their feet for visual signs of injury every day. If any of the study participants identified an abnormality, researchers instructed them to call the study nurse.
Just as in the previous work by Lavery, et al., the temperature monitoring treatment group used the TempTouch to measure six sites on each foot twice a day.14 They compared temperature differences between left and right feet. Researchers used temperature differences of greater than 4°F to identify an abnormality, and patients were asked to reduce their activity until their temperatures returned to a normal range.
During the 18-month evaluation period, 8.4 percent (19) of the study participants developed foot wounds. Of these, 12.2 percent (14) ulcerated in the standard therapy group and 4.7 percent (five) developed foot ulcers in the temperature monitoring treatment group. This represents a three-fold reduction in ulceration. The incidence of foot ulcers was much lower in Armstrong’s study because the majority (82 percent controls and 85 percent of temperature patients) of study participants had sensory neuropathy and foot deformities. In Lavery’s study, all of the patients had a history of foot ulceration in comparison to about 15 percent in Armstrong’s study.
There are a number of limitations to self-inspection in high-risk patients. Often education focuses on self inspection practices that many patients simply cannot perform. In a study of ulcer risk factors, a large proportion of patients with and without foot ulcers did not have the visual acuity, manual dexterity or joint flexibility to perform simple self examination checks of their feet.
For instance, 49 percent of the patients evaluated could not bend their hip, knee and ankle adequately to see the bottom of the foot or their best corrected vision was impaired to such an extent that they could not identify a 1 cm spot on the sole of the foot. Even if a family member is available to visually inspect the foot, without an objective measure of injury, most laymen will only be able to identify ulcers once they have occurred.16 Even when patients are adequately educated and provided with special mirrors to see the bottom of the foot, by the time most patients identify an abnormality, an ulceration already has developed. The visual signs of inflammation are inadequate to prevent an ulcer.13
These types of limitations also limit some high-risk patients from using a handheld device. The next innovation in this line of work will be a remote temperature monitoring instrument that is similar in size to a bathroom scale. This will allow patients with physical disabilities to have the entire sole of the foot scanned. The data will then be sent to a Web site. The data can be analyzed and a report can be prepared for the patients and their healthcare providers that can be accessed via the company’s Web site. This new device is being beta tested and should be commercially available in the next year.
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