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 patients with nerve injury, chronic nerve compression, and neuropathy. We evaluated the Semmes-Weinstein nylon monofilament (SWM), vibrometry, and the Pressure-Specified Sensory Device (PSSD) (Sensory Management Services LLC, Baltimore, Maryland) prospectively on the plantar surface of the hallux, bilaterally, in 35 patients with peripheral nerve problems related to nerve compression and neuropathy. Five patients had carpal tunnel syndrome and, therefore, had normal hallux measurements. Normative data for the SWM were obtained for 59 age-stratified people. A moderately strong Pearson product moment correlation was found for large-fiber nerve function between the PSSD and the SWM and between the PSSD and vibrometry. However, when these functions were compared with 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 test results were obtained for the hallux in 0% of normal feet when the PSSD was used, in 20% when vibrometry was used, and in 30% when the SWM was used as the test instrument. The PSSD was the most sensitive in identifying the presence of a large-fiber peripheral nerve problem in patients with pain or paresthesia in the foot related to the posterior tibial nerve.