Comparison of Measures of Large-Fiber Nerve Function in Patients with Chronic Nerve Compression and Neuropathy

Measurement of large-fiber peripheral nerve function is critical to the assessment of the patient with nerve injury, chronic nerve compression, and/or neuropathy. Available for this purpose in the surgeon's office setting are the Semmes-Weinstein nylon monofilaments (SWM), vibrometry, and the Pressure-Specified Sensory Device (PSSD). These three measurement devices have not previously been directly compared to each other in a given patient population to determine their relative sensitivity/specificity characteristics. The hypothesis tested was that there was no difference in ability to detect a clinical problem related to large-fiber dysfunction between any of these three test devices.

The reported study evaluated each of these three neurosensory testing devices prospectively on the plantar surface of the hallux in 35 patients with peripheral nerve problems related to nerve compression or neuropathy. Five of these patients had carpal tunnel syndrome, and therefore had normal hallux measurements. Normative data for the SWM for the foot were obtained in 59 age-stratified people being evaluated for non-peripheral nerve, “routine,” foot problems.

A moderately strong Pearson correlation coefficient for large-fiber nerve function between the PSSD and SWM (0.545) and between the PSSD and vibrometry (0.514) was found. However, when these functions were compared to normative values for each neurosensory testing technique, sensitivity for detecting the presence of a peripheral nerve problem was 100% for the PSSD, 63% for the SWM, and 30% for vibrometry. False positive tests were obtained for the hallux in normal feet in 0% with the PSSD, in 20% with vibrometry, and in 30% with the SWM. The PSSD was statistically significantly more sensitive in identifying a peripheral nerve problem in the hallux than either the SWM (p < 0.001) or vibrometry (p < 0.001).

In patients symptomatic for pain or paresthesias in the foot related to the posterior tibial nerve, there was a correlation among all three testing devices (SWM, vibrometry, and PSSD) evaluated in this study for the raw data. However when the data were analyzed with respect to normative measurements for each testing device, the neurosensory measurements with the Pressure-Specified Sensory Device were statistically significantly the most sensitive in identifying a clinical problem related to the presence of a large-fiber peripheral nerve dysfunction.