Impact of technical variations on the ring-finger test for carpal tunnel syndrome

Objective: To assess if recording the sensory latencies of the median and ulnar nerves one-by-one (consecutive) or at the same time (simultaneous) in the ring-finger test for carpal tunnel syndrome (CTS) will show equivalent results or if it will lead to a different clinical classification of patients. Methods: We assessed the limits of agreement between the simultaneous and the consecutive method based on the median- ulnar sensory latency difference derived by both methods in 80 subjects and compared the number of minimal CTS cases identified by the two methods. Results: Limits of agreement ranged from -0.23 to 0.29 ms. A significantly higher proportion of subjects with minimal CTS (only detectable by using the comparison test) was found using the simultaneous method (n = 8 and 2, respectively; p = 0.03). Conclusion: The two methods have a poor to moderate agreement as indicated by the range of the limits of agreement (0.5 ms). Significance: Even small methodological changes to the ring-finger test can lead to results with different clinical meaning in the same individual and one should be aware of which method was used when interpreting results. (C) 2019 International Federation of Clinical Neurophysiology. Published by Elsevier B.V.