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The purpose of this study is to examine the variability in sensory test of tactile results using Semmes-Weinstein monofilament (SWM). At present, several methods for measuring the tactile sensitivity are clinically used in diabetic peripheral neuropathy screening. One of these methods is a touch test that uses a device with nylon SWMs, i.e., SWMs embedded in a plastic handle. A small pushing force is applied at the handle to bow the filaments. Because of its ease and simplicity, the SWM test is conducted at the patient's bedside in a hospital. However, previous studies have reported some problems with this test. Studies have shown variations in the measured data, and it is uncertain whether these variations are caused by mechanical properties of the nylon fiber or by the motion of the operator's hands. We carried out two experiments to examine the effect of (1) the variability caused by the human operator conducting the SWM test on the test results and (2) the number of compressions of the SWM on the test results. In experiment 1, we measured the velocity of the operator's hand motion and the buckling force of the SWMs. The results showed variability in the hand motion of the operator conducting the SWM tests. In experiment 2, we measured the buckling force of the SWMs under a controlled velocity. We compared the buckling force of the SWMs through a number of trials. These results showed that the buckling force gradually decreases as the number of test cycles increase. In conclusion, we find that the accuracy of the SWM tests is a factor of the number of test cycles. Additionally, manual training for standardizing skills of medical staff members needs to be developed. Furthermore, the characteristics of the SWMs deteriorated over time. In future work, we aimto find a solution to minimize the variability in the SWM test results and develop a new testing system that uses tactile sensibility for diabetic peripheral neuropathy screening.

The purpose of this study is to develop smart equipment to quantify plantar tactile sensibility for the early diagnosis and tracking of peripheral neuropathy caused by diabetes mellitus. In this paper, we offer a new testing system that is composed of a plantar tactile stimulation platform with a small moving contactor to stretch the skin tangentially, a response switch for each tactile stimulus, a motor control box, and a personal computer (PC) for psychophysical data processing. This quantitative sensory testing system has detailed measurements available and is easy to use compared with the conventional testing devices, such as von Frey monofilaments, pin-prick testing devices, and current perception threshold testers. When using our testing system in a weight-bearing position, we observed that the plantar tactile thresholds for the tangential stretching stimulus on the plantar surface of the foot ranged from approximately 10 um to 30 um for healthy subjects. However, the threshold for a subject with diabetes was nearly three times higher than that for healthy subjects. The significant difference between these values suggests that the plantar sensory evaluation system using the lateral skin stretch stimulation can be used for early diagnosis, for the accurate staging of diabetic neuropathy, and for evaluating its progression noninvasively in a clinic and at home.