Hardness of Plantar Skin in Diabetic Neuropathic Feet

To evaluate if skin hardness in diabetic neuropathic feet was increased and if its eventual modifications could be correlated to the severity of neuropathy, we studied a group of diabetic outpatients with and without neuropathy. Patients, selected among those who were attending their routine screening for diabetic neuropathy at our diabetologic clinic, were divided into two groups according to the presence (ND+) or absence (ND−) of diabetic neuropathy with the criteria of the S. Antonio Consensus Conference on Diabetic Neuropathy. Patients then underwent an evaluation of vibration perception threshold (VPT) by means of a biotesiometer, measurement of skin hardness (DMT) by means of a durometer, and transcutaneous oxygen tension (TcPO2) determination. VPT was determined at allux (VPT-A) and external malleolus (VPT-M), DMT was measured at heel (DMT-H), at medial (DMT-M) and lateral (DMT-L) midfoot, and at posterior midcalf (DTM-C) as a control site; TcPO2 was evaluated at dorsum (TcPO2-D) and at medial midfoot (TcPO2-M), respectively. All measurements were performed on the nondominant side with the patients supine. Patients were compared with age and gender-matched healthy volunteers (Controls), who underwent the same evaluations in the same order. ND+ patients showed higher values of VPT than ND− and Controls, both at first toe and at malleolus analysis of variance (ANOVA) p < 0.01), as well of DMT in all the three sites explored (ANOVA, p < 0.01). Moreover, ND+ showed no difference in DMT among the sites, while both in ND− and in controls DMT-M was significantly (p < 0.05) lower than DMT-H and DMT-L. No difference among the three groups were observed in TcPO2 measurements, and no difference in DMT-C was observed either. A significant correlation was observed between DMT-H and VPT-M (r2 = 0.516) and between DMT-M and VPT-A (r2 = 0.624) in ND+ patients. Skin hardness was diffusely increased in ND+ patients, and this increase strongly correlates with the severity of neuropathy. Simple, noninvasive determination of skin hardness could identify patient at potential risk to develop neuropathic foot ulcers.