The sites include mid-dorsum of the foot; sole of the foot; first, third, and fifth metatarsal heads; first metatarsal-cuneiform joint; talonavicular joint; and heel. Patient monitoring with the infrared thermometer does not include the 3 points on the plantar aspect of the toes (only the 7 remaining points). Healthcare professionals’ 10-point monofilament exam for neuropathy can include all 10 points illustrated with 4 or more negative sites (unable to feel the monofilament) diagnostic for neuropathy.
These studies and previous publications were assessed in 2 separate technical reviews and meta-analyses. Arad et al18 evaluated the preventive techniques in patients at high risk for a diabetic foot ulcer and concluded that personal or patient use of thermometry was the most robust preventive intervention. More specifically, Houghton et al19 utilized a systematic review and meta-analysis that specifically identified strong evidence supporting the use of infrared thermometry for patient self-monitoring.
ELEVATED PERIWOUND SKIN TEMPERATURE AND INFECTION
Delayed healing of wounds not only prolongs patient distress and discomfort, but can also increase the risk of complications and add to healthcare costs.20,21 Previous studies have demonstrated that chronic wounds infected with bacteria have reduced tensile strength and contribute to prolonged healing time. Failure to achieve wound healing in a timely fashion is multifactorial, and periwound deep and surrounding infection is one of the most significant contributors to delayed healing.22–24
Sibbald et al25 developed a clinical guide to standardize the assessment of superficial critical colonization and deep/surrounding chronic wound infection. The assessment categorizes bacterial wound damage into superficial critical colonization and deep and surrounding infection that can be treated topically, and the latter requiring systemic treatment. Each category has a unique set of clinical signs. Three or more of the 5 NERDS signs are required to diagnose superficial critical colonization: Nonhealing wound status—not 30% smaller in 4 weeks, increased Exudate, Red and friable granulation tissue, necrotic Debris, and/or Smell (NERDS). If 3 or more of these signs are present, topical antiseptics (silver, iodine, polyhexamethylene biguanide, honey, and a combination of methylene blue-crystal violet) are indicated for treatment. Signs and symptoms of deep and surrounding infection include increased wound Size, increased periwound Temperature, Os (probing to bone), New areas of breakdown, Erythema and/or edema (cellulitis), increased Exudate, and Smell (STONEES). If 3 or more of these signs are present, the wound likely has a deep and surrounding infection requiring systemic antimicrobials (oral or intravenous) for treatment.
It is important to note that quantitative bacterial count on skin biopsy is still considered the criterion standard for deep and surrounding infection. This specialized skin biopsy is predominantly a research tool and not routinely performed in clinical practice.26 Instead, semiquantitative wound swabs are more commonly ordered because of their relative accuracy (Levine technique), accessibility, and lower cost.20,27–29 Recently, a validation study of the NERDS and STONEES criteria by Woo and Sibbald30 illustrated that elevated temperature gradient was 8 times more likely to represent a deep and surrounding infection compared with the mirror-image temperature.30 This is the highest association, with all the other STONEES criteria individually being 2 to 5 times more likely to be associated with a deep and surrounding infection. The validation of STONEES had a high specificity and sensitivity for the entire population studied (92), as well as for the subpopulation of 44 individuals with diabetes.30
Because repeated trauma can also result in an elevated local temperature, 2 other STONEES signs are required to make a diagnosis of infection. Elevated temperatures alone, as the authors have previously discussed, may be due to repetitive trauma in the neuropathic foot. The diagnostic accuracy of palpation for an elevated skin temperature is quite limited because it is often more subjective than objective.31
Conventional mercury or electronic thermometers are difficult to attach to the wound or periwound area, require time to be calibrated, and are prone to lower or inaccurate readings because of the limited surface for direct contact.32
A handheld noncontact infrared thermometer has the potential to provide an accurate, objective, and quantitative measurement of skin surface temperature.32 Recently, Fierheller and Sibbald33 illustrated the relationship between increased periwound skin temperature and local wound infection. In this study, the use of the handheld infrared thermometer for 22 patients with leg ulcers was validated. Statistical analysis of the participant’s wound temperature data identified a significant relationship between deep and surrounding infection and quantitative increase in periwound temperature. In the absence of deep and superficial infection, the authors reported a mean temperature difference between periwound skin and an equivalent contralateral control site to be equal to or less than 2° F (0.38° F [SD, 0.89° F]). When deep and surrounding infection was present, the mean periwound skin temperature was elevated by more than 2° F (4.43° F [SD, 2.44° F]). It is well known that skin temperature varies depending on the body location, blood flow, and external environment. The results of this study demonstrated that skin temperatures were not significantly different between nonwounded, wounded control, or wounded, noninfected periwound sites.33 In the authors’ clinical experience and based on the STONEES evaluation study,30 benchmarked temperature elevation of 3° F or greater indicated a potential deep or surrounding infection and a case for further investigation. Using the STONEES mnemonic introduced in this study, any 3 clinical signs can indicate deep and surrounding skin infection. An increased temperature is not an absolute requirement to diagnose infection; however, the individual factor analysis indicated that temperature was the most important single indicator, but this still needs to be combined with 2 other clinical signs.
Handheld noncontact infrared thermometers are effective tools for identifying and quantifying the temperature associated with chronic wound infections. Incorporating infrared thermometers as part of the routine wound assessment provides an objective measurement of periwound skin temperature. The infrared thermometer can assist the healthcare practitioner with early detection of deep or surrounding and spreading infection, facilitating timely management. In addition to repetitive trauma and infection, infrared thermometry can also measure deep inflammatory processes including the Charcot joint.
SKIN TEMPERATURE AND ACUTE CHARCOT
Charcot joint is a progressive musculoskeletal condition that specifically affects neurotrophic feet. As previously mentioned, neuropathy consists of the 3 “SAM” components. In addition to diabetes mellitus, Charcot joints may also be associated complications of other causes of neuropathy including trauma, syphilis, chronic alcoholism, leprosy, meningomyelocele, spinal cord injury, syringomyelia, renal dialysis, and congenital neuropathies.
An acute Charcot joint is the result of an acute inflammatory process associated with an increased localized surface temperature of 4° F to 15° F or even higher. An X-ray examination of the foot can usually rule out other causes of trauma (fracture, foreign body), as well as deep infection. The acute inflammatory process in a neuropathic joint is probably initiated by repetitive trauma and results in multiple fractures of the bone, leading to resorption of the bone matrix. When the inflammatory process is controlled, the skin surface temperature normalizes, and the bone solidifies often with a permanent deformity. To resolve the acute process with minimal bone destruction, weight bearing should be restricted (by offloading the joint) with the use of a wheelchair or gradually introducing plantar pressure redistribution devices, including a contact cast or removable cast walker.
Patients with Charcot joint deformity can present with a wide variety of clinical features that are primarily dependent on the stage of the disease. The acute stage is usually characterized by ill-defined unilateral pain (but acute Charcot joints can be painless), edema, erythema, and associated warmth to the affected area. As the Charcot process evolves into the postacute stage, inflammation and the skin temperature tend to decrease.
Determining the complete resolution of Charcot joint is often very difficult. As Charcot joint resolves, the residual signs of inflammation are subtle and difficult to quantify and monitor. Numerous studies have reported the utility of skin temperature monitoring in Charcot joint, especially to monitor healing, and the ability to gradually resume weight bearing is often monitored in specialty diabetic foot clinics.12,34–36
In 1997, Armstrong et al36 conducted a study to monitor the healing of acute Charcot joint with infrared dermal thermometry. Thirty-nine individuals diagnosed with acute Charcot joint were selected to participate in the study. The diagnosis was made primarily based on clinical, radiographic, and dermal thermometric features. Participants with comorbidities such as osteomyelitis, chronic Charcot joint, bilateral involvement, or open reduction of the fracture were excluded from the analysis.
The researchers also described the location of Charcot joint using the Sanders pattern classification. The classification is based on anatomical locations in the foot and ankle (metatarsal heads, midfoot, heel, and ankle). The 39 participants were treated with a standard protocol involving serial total contact casting. As the disease improved, participants were issued removable cast walkers and eventually prescription therapeutic shoe gear. All casts were checked at regular time intervals by study staff to ensure proper fit and appropriate plantar pressure redistribution. Furthermore, the casts were discontinued, and therapeutic footwear introduced if clinical and radiographic signs improved, as well as a return to the same temperature as the contralateral limb.
Skin temperatures were monitored using a portable infrared thermometer, and readings were recorded from 7 sites (Figure 1). These included the soles of both feet, specifically over the first, third, and fifth metatarsal heads; first metatarsal-cuneiform joint; talonavicular joint; cuboid; and heel. The researchers compared the results to the mirror image on the contralateral limb. The temperature difference between the pathological limb and contralateral side was calculated and recorded. A positive value suggested that the temperature of the affected Charcot foot was higher than the contralateral side. The authors reported that the mean skin temperature difference for all participants at initial presentation was 8.8° F+/-2.3° F (range, 5.1° F–14.7° F). In 92% of the participants, the region on the foot with the maximum skin temperature difference correlated to the site of maximum radiographically evident Charcot joint deformity. The skin temperature difference gradually decreased during total contact cast therapy. As the participants transitioned to the prescription shoe gear, the skin temperature difference normalized to a near-zero value.
The results of this study suggest that elevated skin temperatures are directly correlated with location of acute Charcot joint. The temperature differences decrease as acute Charcot joint resolves and transitions into a postacute state. Infrared thermometry can be used to detect subtle temperature differences that can persist for weeks to months, even when no palpable differences can be perceived. During the follow-up period of the study, no recurrences of Charcot joint were reported. The low incidence of recurrences was a result of immobilization of the foot in a removable cast walker or total contact cast if a difference of 4° F or more was observed.
More recently, clinicians and scientists have suggested that a “stress test” might be a promising way forward to identify early Charcot arthropathy. Najafi et al37 measured preambulation and postambulation skin temperatures following a course of 50 and 150 steps. Patients with Charcot arthropathy had high temperatures that remained high in the postambulation period. However, those with peripheral neuropathy and no Charcot arthropathy displayed a reduction in plantar midfoot skin temperature. The results imply that reduced activity in a susceptible area not involved with an active Charcot reduces the reaction to repetitive stress.
Temperature differences as small as 4° F are difficult for healthcare professionals and patients to perceive simply by palpation.31 Temperature monitoring utilizing infrared thermometers is quantitative and can be recorded quickly. Because the prevalence of reinjury in individuals with Charcot joint is high, a quantitative method to identify “at risk” patients can significantly reduce the chance of recurrence.
Infrared thermometry is a safe and effective method to measure the skin surface temperature. Patients at high risk for diabetic foot ulcers can use daily infrared thermometer monitoring for an increased temperature greater than 4° F over the mirror image on the other foot. The increased temperature is a warning of potential foot ulceration and the need to restrict activities. Because the industrial infrared devices are less than $100, patients may pay for them (and several have in the authors’ experience). There is RCT, systematic review, and meta-analysis evidence for patient-directed preventive foot care utilizing noncontact infrared thermometry. The ease of use and the relative low cost have the potential to make them readily available to patients along with the current use of glucose monitors.
Noncontact low-cost thermometers are suitable for everyday clinical practice and with a high distance-to-spot ratio can decrease the risk of iatrogenic cross-contamination and potential infections. Differences in mirror-image readings using the Fahrenheit scale are easier to detect a 3° F–4° F temperature difference related to deep and surrounding infection, deep inflammation, or unequal vascular supply. If a foot is closed (intact skin) and hot, think of an acute Charcot joint, and if it is open (open wound) and hot, think of a deep and surrounding infection or repetitive trauma.
An area of increased localized skin surface temperature around a wound compared with a mirror-image temperature usually indicates deep and surrounding infection, but unequal vascular supply must also be considered as an additional diagnostic possibility. For deep and surrounding infection, check for 2 or more additional STONEES criteria. Another diagnostic aid is the presence of increased local pain without another reason that can be a symptom supporting the potential for deep and surrounding infection.
If a neuropathic foot is nonwounded, warm, and swollen without ulceration, an acute Charcot foot should be considered in the differential diagnosis. The clinical suspicion can be confirmed with an x-ray or magnetic resonance imaging. Monitoring of the skin surface temperature to achieve normalization compared with the mirror image can be a sentinel clue for remobilization and resolution of the acute and unstable Charcot change.
Skin assessment with an infrared thermometer is adaptable to routine wound care practice and home health. Furthermore, patients should be educated about the use of these infrared thermometers, especially because inexpensive commercially available infrared thermometers yield similar results as the criterion-standard device.
- Inexpensive commercially available infrared thermometers are a useful instrument for wound care practice.
- Noncontact infrared thermometers can detect localized increases in skin surface temperature comparable to scientific grade instruments.
- Persons with diabetes and a high-risk foot can utilize daily infrared monitoring of the plantar aspect of the foot to detect localized temperature increases, restrict ambulation, and decrease the incidence of repetitive trauma–initiated neurotropic foot ulcers.
- A high temperature elevation (4° F–15° F) over themirror image on the opposite foot in a person with diabetes without a foot ulcer may indicate an acute Charcot foot.
1. Blundell S, Blundell K. Concepts in Modern Physics. Blundell K: Oxford University Press; 2006.
2. Osio C, Carnelli V. Comparative study of body temperature measured with a non-contact infrared thermometer versus conventional devices. The first Italian study on 90 pediatric patients. Minerva Pediatr 2007; 59: 327–36.
3. Teran C, Torrez-Llanos J, Teran-Miranda T, Balderrama C, Shah N, Villarroel P. Clinical accuracy of a non-contact infrared skin thermometer in paediatric practice. Child Care Health Dev 2012; 38: 471–6.
4. 4. Mufti A, Coutts P, Sibbald RG. Validation of commercially available infrared thermometers for measuring skin surface temperature associated with deep and surrounding wound infection. Adv Skin Wound Care 2014; 28: 11–6.
5. Thomas PK. Classification, differential diagnosis, and staging of diabetic peripheral neuropathy. Diabetes 1997; 46 (Suppl 2): S54–7.
6. Dyck PJ, Kratz KM, Karnes JL, et al. The prevalence by staged severity of various types of diabetic neuropathy, retinopathy, and nephropathy in a population-based cohort: the Rochester Diabetic Neuropathy Study. Neurology 1993; 43: 817–24.
7. Singleton JR, Smith AG, Bromberg MB. Increased prevalence of impaired glucose tolerance in patients with painful sensory neuropathy. Diabetes Care 2001; 24: 1448–53.
8. Tesfaye S, Chaturvedi N, Eaton SE, et al. Vascular risk factors and diabetic neuropathy. N Engl J Med 2005; 352: 341–50.
9. Armstrong DG, Lavery LA, Wu S, Boulton AJ. Evaluation of removable and irremovable cast walkers in the healing of diabetic foot wounds: a randomized controlled trial. Diabetes Care 2005; 28: 551–4.
10. Orsted HL, Searles GE, Trowell H, Shapera L, Miller P, Rahman J. Best practice recommendations for the prevention, diagnosis, and treatment of diabetic foot ulcers: update 2006. Adv Skin Wound Care 2007; 20: 655–69.
11. Lavery LA, Peters EJ, Armstrong DG. What are the most effective interventions in preventing diabetic foot ulcers? Int Wound J 2008; 5: 425–33.
12. Armstrong DG, Lavery LA, Liswood PJ, Todd WF, Tredwell JA. Infrared dermal thermometry for the high-risk diabetic foot. Phys Ther 1997; 77: 169–75.
13. Clark R, Goff M, Hughes J, Klenerman L. Thermography and pedobarography in the assessment of tissue damage in neuropathic & atherosclerotic feet. Thermology 1988; 3: 15–20.
14. Armstrong DG, Lavery LA. Predicting neuropathic ulceration with infrared dermal thermometry. J Am Podiatr Med Assoc 1997; 87: 336–7.
15. Lavery LA, Higgins KR, Lanctot DR, et al. Home monitoring of foot skin temperatures to prevent ulceration. Diabetes Care 2004; 27: 2642–7.
16. Lavery LA, Higgins KR, Lanctot DR, et al. Preventing diabetic foot ulcer recurrence in high-risk patients: use of temperature monitoring as a self-assessment tool. Diabetes Care 2007; 30 (1): 14–20.
17. Armstrong DG, Holtz-Neiderer K, Wendel C, Mohler MJ, Kimbriel HR, Lavery LA. Skin temperature monitoring reduces the risk for diabetic foot ulceration in high-risk patients. Am J Med 2007; 120: 1042–6.
18. Arad Y, Fonseca V, Peters A, Vinik A. Beyond the monofilament for the insensate diabetic foot: a systematic review of randomized trials to prevent the occurrence of plantar foot ulcers in patients with diabetes. Diabetes Care 2011; 34: 1041–6.
19. Houghton VJ, Bower VM, Chant DC. Is an increase in skin temperature predictive of neuropathic foot ulceration in people with diabetes? A systematic review and meta-analysis. J Foot Ankle Res 2013; 6 (1): 31.
20. Dow G. Bacterial swabs and the chronic wound: when, how, and what do they mean. Ostomy Wound Manage 2003; 49 (5): 8–13.
21. Bowler P, Duerden B, Armstrong D. Wound microbiology and associated approaches to wound management. Clin Microbiol Rev 2001; 14: 244–69.
22. Robson MC. Wound infection: a failure of wound healing caused by an imbalance of bacteria. Surg Clin North Am 1997; 77: 637–50.
23. Singer AJ, McClain SA. Persistent wound infection delays epidermal maturation and increases scarring in thermal burns. Wound Repair Regen 2002; 10: 372–7.
24. Stephens P, Wall IB, Wilson M, et al. Anaerobic cocci populating the deep tissues of chronic wounds impair cellular wound healing responses in vitro. Br J Dermatol 2003; 148: 456–66.
25. Sibbald RG, Woo K, Ayello EA. Increased bacterial burden and infection: the story of NERDS and STONES. Adv Skin Wound Care 2006; 19: 447–61.
26. Serena T, Robson MC, Cooper DM, et al. Lack of reliability of clinical/visual assessment of chronic wound infection: the incidence of biopsy-proven infection in venous leg ulcers. Wounds 2006; 18: 197–202.
27. Pellizzer G, Strazzabosco M, Presi S, et al. Deep tissue biopsy vs. superficial swab culture monitoring in the microbiological assessment of limbthreatening diabetic foot infection. Diabet Med 2001; 18: 822–7.
28. Slater R, Lazarovitch T, Boldur I, et al. Swab cultures accurately identify bacterial pathogens in diabetic foot wounds not involving bone. Diabet Med 2004; 21: 705–9.
29. Sullivan P, Conner-Kerr T, Hamilton H, Smith E, Tefertiller C, Webb A. Assessment of wound bioburden development in a rat acute wound model: quantitative swab versus tissue biopsy. Wounds 2004; 16: 115–23.
30. Woo KY, Sibbald RG. A cross-sectional validation study of using NERDS and STONEES to assess bacterial burden. Ostomy Wound Manage 2009; 55 (8): 40–8.
31. Murff RT, Armstrong DG, Lanctot D, Lavery LA, Athanasiou KA. How effective is manual palpation in detecting subtle temperature differences? Clin Podiatr Med Surg 1998; 15 (1): 151–4.
32. Romanelli M, Gaggio G, Coluccia M, Rizzello F, Piaggesi A. Technological advances in wound bed measurements. Wounds 2002; 14 (2): 58–66.
33. Fierheller M, Sibbald RG. A clinical investigation into the relationship between increased periwound skin temperature and local wound infection in patients with chronic leg ulcers. Adv Skin Wound Care 2010; 23: 369–79.
34. Armstrong DG, Todd WF, Lavery LA, Harkless LB, Bushman TR. The natural history of acute Charcot’s arthropathy in a diabetic foot specialty clinic. J Am Podiatr Med Assoc 1997; 87: 272–8.
35. Sandrow RE, Torg JS, Lapayowker MS, Resnick EJ. The use of thermography in the early diagnosis of neuropathic arthropathy in the feet of diabetics. Clin Orthop Relat Res 1972; 88: 31–3.
36. Armstrong D, Lavery L. Monitoring healing of acute Charcot’s arthropathy with infrared dermal thermometry. J Rehabil Res Dev 1997; 34: 317–21.
37. Najafi B, Wrobel JS, Grewal G, et al. Plantar temperature response to walking in diabetes with and without acute Charcot: the Charcot Activity Response Test. J Aging Res 2012; 2012: 140968.
Keywords:© 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins. All world rights reserved.
infrared thermometers; wound infection; diabetic foot monitoring; Charcot foot