Liquid crystal thermography in neuropathic assessment of the diabetic foot.

Abstract

Primary aetiologic factors of diabetic foot disease include peripheral neuropathy and peripheral vascular disease. Assessment of circulation, neuropathy, and foot pressure is employed routinely to determine the risk of foot ulceration in the patient with diabetes mellitus. Routine neuropathic evaluation includes assessment of sensory loss in the plantar skin of the foot using both the Semmes Weinstein monofilament and the biothesiometer. Progressive degeneration of sensory nerve pathways is thought to affect thermoreceptors and mechanoreceptors. However, thermological measurements of the foot to assess responses to thermal stimuli and cutaneous thermal discrimination threshold are relatively uncommon. Recent improvements in liquid crystal technology (LCT) including insensitivity to pressure, faster response times, lower cost and fast image acquisition offer potential for routine thermographic assessment of the diabetic foot. The present study was designed to evaluate if an association exists between abnormal plantar thermal images and sensory loss under conditions of normal loading. The system comprises a robust measurement platform, thermochromic liquid crystal polyester sheet (TLC), instrumentation and analysis software. In vitro calibration was performed to characterise three physical forms of TLC on the basis of linearity, hysteresis, pressure sensitivity and response time. An in vivo pilot evaluation study of the system was performed using three sub-groups (i) neuropathic diabetic (n=30), (ii) non neuropathic diabetic (n=30) and (iii) a healthy control group (n=30). The principal results of this study indicate raised plantar temperatures for the diabetic groups at baseline and post stress relative to the control group. Furthermore, poor recovery response to thermal stimulus in the neuropathic diabetic group suggests degeneration of thermoreceptors. Thus by assessing the thermal parameters at the same sites as that of sensory testing, the new LCT based approach appears capable of providing an alternative confirmation of clinical neuropathy and offers potential as an improved method compared to existing techniques.