ABSTRACT
Recently, several methods have been promoted as reliable, objective and inexpensive in testing for signs of CTS in the workplace. Measurements of distal latency are traditionally made by stimulating a peripheral nerve with an electrical impulse applied to the skin over the course of the nerve in question, and measuring the conduction time using a second set of skin electrodes placed over a muscle innervated by the nerve and distal to the point of stimulation. Conduction of the stimulus along the nerve to the muscle causes muscle contraction for the motor fiber testing and the resulting muscle action potential is detected by the skin electrodes, amplified and the signal displayed on an oscilloscope screen. Measurement of the distance between the stimulus and the onset of the action potential on the oscilloscope screen allow calculation of the nerve conduction time, or latency. A portable electroneurometer, such as the NervePace-100, measures the distal latency of the motor nerve across the carpal tunnel and displays the value in milliseconds on a LED readout. Despite considerable interest in these systems, little formal research has been conducted to determine whether they can reliably detect physiologic signs associated with CTS (Grant, Congleton, Kuppa, Lessard, and Hutchingson, 1992). Although standard nerve conduction studies are the most sensitive objective test detecting peripheral compression neuropathy in CTS, they are reported to have a false negative rate ranging between 5 and 20% (Melvin, Schuchmann, and Lanese, 1973). In comparison to more formal nerve studies, the electroneurometer gives no information about the sensory conduction of the median nerve, so that the question remains whether the electroneurometer would adequately reflect the condition of the nerve. These considerations are complicated by the findings that sensory changes often proceed motor abnormalities in CTS and that as many as 20% of cases with operatively proven CTS may have no motor abnormalities (Chrisanne, 1987 and Liebhuber, 1986).
