Testing for Loss of Protective Sensation in Patients with Foot Ulceration

Current recommendations for the prevention of foot ulceration and amputation include screening at-risk individuals by testing for loss of protective sensation at eight sites using 10-g (5.07) nylon monofilaments. Yet measurement of the cutaneous pressure threshold to differentiate one-point from two-point static touch stimuli may allow identification of these at-risk individuals earlier in the clinical course of diabetic neuropathy. The present study tested this hypothesis using a prospective, cross-sectional, multicenter design that included sensibility testing of 496 patients with diabetic neuropathy, 17 of whom had a history of ulceration or amputation. Considering the cutaneous pressure threshold of the 5.07 Semmes-Weinstein nylon monofilament to be equivalent to the 95 g/mm2 one-point static touch measured using the Pressure-Specified Sensory Device (Sensory Management Services LLC, Baltimore, Maryland), only 3 of these 17 patients with a history of foot ulceration or amputation would have been identified using the Semmes-Weinstein nylon monofilament screening technique. In contrast, using the Pressure-Specified Sensory Device, all 17 patients were identified as having abnormal sensibility, defined as greater than the 99% confidence limit for age, for two-point static touch on the hallux pulp. We conclude that patients at risk for foot ulceration can best be identified by actual measurement of the cutaneous sensibility of the hallux pulp. (J Am Podiatr Med Assoc 95(5): 469–474, 2005)

Evaluation of Pressure Threshold Prior to Foot Ulceration

A prospective study of 29 patients with diabetic neuropathy and 47 nondiabetic patients with tarsal tunnel syndrome were evaluated with computer-assisted neurosensory testing at three sites on the foot. The sensitivity and specificity of one-point static touch thresholds for identifying the presence of large fiber axonal loss was done using the calculated thresholds for monofilaments derived from their markings. The sensitivity for one-point static touch in identifying axonal loss was 33% for the 5.07, 38% for the 4.93, 50% for the 4.17, and 60% for the 4.08 monofilament-equivalent, with a specificity of 100% at each level. Therefore, one-point static touch testing, even using monofilaments thinner than 5.07, has a high percentage of false-negative results in identifying patients with axonal loss. (J Am Podiatr Med Assoc 91(10): 508-514, 2001)

The Relationships between Skin Hardness, Pressure Perception and two-Point Discrimination in the Fingertip

With the recent introduction of computer-assisted sensibility testing devices, it is possible to investigate the hypothesis that the neurological mechanisms responsible for perception of pressure and two-point discrimination are influenced by skin hardness. This study examined the relationships between the skin hardness of the human index and little finger pulp and the perception of pressure in 25 adults. Skin hardness was measured using the Derma-Durometer. Pressure perception was measured with the Pressure-Specified Sensory Device®* for both static and moving touch stimuli and for two-point discrimination. The mean hardness of the fingertip pulp was 12.5 ± 0.6 gm/mm2. There was no statistically significant difference in hardness between the dominant and non-dominant, right and left, index and little, or male and female fingertips. Skin hardness was independent of age for this population. The highest correlation, which was r = 0.46, was found between the cutaneous pressure threshold for one-point static touch and skin hardness. While this degree of correlation is significant at the P < 0.02 level, the r2 = 21%, demonstrating that this degree of correlation leaves 79% of the variability unexplained. These results suggest a physical interaction between mechanoreceptors and dermis that is only partially explained by the hardness of the skin.