OBJECTIVE: This cross-sectional study aims to determine the accuracy of using a surface electrode compared with using a needle electrode in the determination of the latency, amplitude, and duration of the compound motor action potential and nerve conduction velocity of the radial nerve.
METHODS: A cohort of 42 males and 30 females consisting of patients from the Philippine General Hospital referred for electrodiagnostic studies of the upper extremity and healthy volunteers were included in the study. The compound motor action potential of the radial nerve in each participant was determined using the surface electrode technique and the mono polar needle technique, and the results were compared. The man outcome measures were: compound motor action potential amplitude, latency, duration, and nerve conduction velocity; sensitivity; specificity; and agreement between the two techniques under investigation.
RESULTS: When all parameters in the nerve conduction studies were considered, the sensitivity of the surface electrode compared with the mono polar needle electrode in determining radial nerve abnormalities was 46.14% (95% Confidence Interval (CI) 0.27 - 0.65), with a specificity of 82.61% (95% CI 0.72 - 0.94) and an overall diagnostic accuracy of 69.44%. When the parameters were taken individually, analysis of the latency showed sensitivity of 60% (95% CI 0.17 - 1.03), and specificity of 100%, with overall diagnostic accuracy of 97.22%. The test for amplitude yielded sensitivity of 50% (95% CI 0.1 - 0.90) and specificity of 100%. The overall diagnostic accuracy was 95.83%. Analysis of the duration showed a sensitivity of 71.43% (95% CI 0.38 - 1.05) and specificity of 100%, with overall diagnostic accuracy of 97.22%. The nerve conduction velocity alone showed sensitivity of 55% (95% CI 0.33 - 0.77), specificity of 84.61% (95% CI 0.75 - 0.94), and overall diagnostic accuracy of 76.39%. The kappa test revealed a fair association or agreement when all the parameters of the compound motor action potential were taken into consideration (k=0.30), moderate association between the surface and the needle electrode in nerve conduction velocity (k=0.40), a substantial association in nerve conduction velocity (k=0.40), a substantial association in amplitude (k=0.65) and latency (k=0.74), and a high association between the two techniques for the duration (k=0.81).
CONCLUSIONS: In the comparison of the surface electrode and the mono polar needle electrode techniques in the determination of the compound motor action potential of the radial nerve, the parameters have high specificity and a high probability of a negative test in individuals who are disease-free. The kappa test indicated a fair association between the two techniques. When the parameters of compound motor action potential are taken separately, the latency, amplitude, duration and nerve conduction velocity of the radial nerve have a high probability of positive test results in people with disease and a high probability of negative test results in people with no disease. The study showed that the surface electrode technique is a fair to good alternative to the needle electrode when conducting a radial motor nerve study.