Background and Purposes: The primary purpose of this study is to determine the effect of combining the measurements of Vibration Perception Threshold (VPI) and Semmes Weinstein Monofilament (SWM), on predicting the abnormality of the Mixed Sensorimotor Potential (MSP) of the medial and lateral plantar nerves in patients with type two diabetes mellitus. The secondary purpose is to determine the segments at the terminal branches of both nerves where combining VPT and SWM highly predict MSP of both nerves. Methods: Two age-matched (40 to 75 years of age) study groups were formed; group A (mean age of 51 years) participants were healthy volunteers with normal MSP of the medial and lateral plantar nerves, and group B (mean age 59 years) participants were patients with type two diabetes mellitus with abnormal medial and lateral plantar MSP. 30 subjects were included in each group. VPT as measured by the Biothesiometer and touch perception threshold as measured by SWM were obtained on six points in the sole of the foot. These points correspond to the dermatomal distribution of the medial and the lateral plantar nerves as follows; the plantar surface of the 1st and 5th toes, the plantar surface of 1st an 5th metatarsals, and the plantar surface of the lateral and medial areas just distal to the heel. The sensitivity, specificity, and the postitive and negative predictive values were obtained for the VPT and SWM in all points both individually and combined. ROC curves were established for VPT and SWM individually and combined to determine the best cutoff points to predict the abnormality of the MSP. Results: Combining VPT and SWM improved the sensitivity to predict the abnormal electrophysiologic response of the MSP of the medial and lateral plantar nerves in all points in both feet. The increased sensitivity was accompanied by little diminution in their corresponding specificity. The points of highest combined sensitivity were the right first and fifth metatarsals with 83.3% and 87%, respectively. The corresponding combined specificity for the right first and fifth metatarsal were 90% and 90%, respectively. The left medial and lateral heel areas sensitivity were 83.3% and 83.3%, respectively, and with corresponding combined specificity of 93.3% and 93.3%, respectively. The plantar aspect of the first and fifth toes combined sensitivity were 80% and 70%, respecitvely with corresponding specificity of 90% and 100%, respectively. The increased sensitivity when both tests are combined is not statistically significant among the terminal segments of both nerves. Conclusions: Combining VPT and SWM on the plantar surface of the foot significantly increases the sensitivity to predict the abnormality of MSP of the medial and lateral plantar nerves.
