Ultrasonographic and thermographic screening for latent inflammation in diabetic foot callus
Introduction
Diabetic foot ulcer is one of the major complications of diabetes, seriously affecting patients’ quality of life and health care costs [1]. It is thus quite urgently needed to establish a novel method of prevention or early diagnosis for diabetic foot ulcer.
Callus is defined as “localized hyperplasia of the horny layer of the epidermis due to pressure or friction” (Dorland's medical dictionary), and is regarded as the most important preulcerative lesion in the diabetic neuropathic foot [2], [3]. Indeed, it was reported that callus formation preceded ulceration in 82.4% of diabetic foot ulcer patients [4]. Murray et al. [5] also reported a relative risk of 11.0 for an ulcer developing under an area of callus in diabetic patients with neuropathy. Notably, foot ulceration may be quite rare in the healthy population although callus is also commonly seen in non-diabetic patients.
Inflammatory changes may be observed surrounding the callus regions when they develop into ulcers. It is difficult to assess inflammation through symptoms such as erythema, swelling or localized warmth in these regions, since the plantar skin has thick layer of stratum corneum. Furthermore, inflammatory pain may occasionally be undetectable in diabetic patients due to sensory disturbance [6]. One of the reasons why callus ulceration mostly occurs in diabetic population may be that these patients often overlook or underestimate inflammation. However, it is yet to be confirmed whether such “asymptomatic inflammation” is certainly unique for diabetic population, not found in non-diabetic patients.
Recent advances of physiological imaging techniques have prompted us to use thermography and ultrasonography for screening increasing skin temperature, deep tissue edema or fluid collection due to inflammation [7], [8]. Localization of inflammation can be specified by thermography, and the severity of inflammation and tissue damage can be estimated by ultrasonography. Especially for diabetic foot ulceration, Edmonds and Foster [2] mentioned that skin breakdown may often be preceded by subcutaneous hematoma or autolytic seroma beneath the callus. Ultrasonography may be very promising for detecting such subcutaneous changes. However, as far as we know, there are no previous researches using thermography or ultrasonography for screening early inflammatory changes in the foot calli.
In the present study, we observed cross-sectional profiles of plantar calli in patients with and without diabetes. We further detected latent inflammation under the calli by physiological imaging techniques such as thermography and ultrasonography, and relationship between the inflammatory findings and presence or absence of diabetes was evaluated.
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Subjects
The subjects included 30 diabetic patients having plantar calli (DM group), and 30 non-diabetic callus patients of matched age and sex (non-DM group). The DM group was recruited from the patients in the Diabetic Foot Outpatient Clinic at the University of Tokyo Hospital. The non-DM group was the volunteers selected by the snowball sampling method.
Diagnosis of associated neuropathy was required as an inclusion criterion for the DM group. It was defined by the diagnostic criteria by Japanese
Results
Forty-six diabetic patients were encountered at the Diabetic Foot Outpatient Clinic during the observation period. Sixteen patients fulfilled the exclusion criteria described above, and the resting 30 were included in this study as the DM group. The non-DM group were matched age and sex.
The demographic data are detailed in Table 1. All the DM group patients were type 2 diabetes. Duration of diabetes was 15.5 (1–31) years, and HbA1c value was 6.7% (5.3–12.4). The proportion of obesity with BMI
Discussion
This is the first paper demonstrating significant versatility of thermography and ultrasonography as screening tools for latent asymptomatic inflammation underneath the foot callus in diabetic patients. Inflammatory change in the callus has been considered as a high risk factor for later ulcer development. In our study, 10% of the calli in the DM group had the inflammatory findings in the physiological imagings, whereas none in the non-DM group.
Edmonds and Foster [17] emphasized importance of
Conflict of interest
There are no conflicts of interest.
Acknowledgments
We express sincere thanks to the DM patients at the Diabetic Foot Outpatient Clinic and the non-DM volunteers. We are also grateful for Professor Junko Sugama and Associate professor Mayumi Okuwa for their fruitful discussion, all the staffs of the Diabetic Foot Outpatient Clinic for their kind help and management for our study, and Dr. Takafumi Kadono for his advice as a dermatologic specialist.
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These authors equally contributed to this work.