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.