Median mixed and sensory nerve conduction studies in carpal tunnel syndrome1

Abstract

Objective: To assess the sensitivities and specificities of velocity differences between median mixed nerve conduction across the wrist (Medmxpw) and (I) median mixed nerve conduction in the forearm (Medmxf) and (II) palm to D2 sensory conduction (MedpD2). Design and Methods: We prospectively studied 67 limbs of patients with clinically definite carpal tunnel syndrome (CTS). Medmxf and Medmxpw were performed by stimulating the median nerve at the elbow and palm respectively and recording at the proximal wrist crease. We also compared conventional median sensory (D2–wrist) and mixed (palm–wrist) tests in all patients. Thirty limbs of asymptomatic subjects served as normal controls and 21 limbs of subjects with other neuropathies served as diseased controls; control data was collected prospectively. Results: The sensitivity of the MedpD2–Medmxpw difference (0.87) was significantly greater than that of the Medmxf–Medmxpw difference (0.61, P<0.001). Both tests were similar and highly specific (0.98 and 0.96, respectively). Conclusions: The MedpD2–Medmxpw study is among the most sensitive and specific electrophysiologic tests for CTS.