Comparison of Borderline Ultrasound and Nerve Conduction Studies for Carpal Tunnel Syndrome.

Abstract

Choosing cutoff values for nerve conduction studies (NCS) and ultrasound cross-sectional area (CSA) in the diagnosis of carpal tunnel syndrome (CTS) is critical in determining the diagnostic accuracy of the tests. The goals of this study were to: (1) determine the sensitivity and specificity of various electrodiagnostic and ultrasound threshold values for diagnosis of CTS; and (2) determine the number of hands that underwent NCS and ultrasound that were within 10% of threshold values. A total of 309 hands of 235 patients were included in this study. Diagnosis of median neuropathy was made based on NCS by the independent physician performing the NCS. Criteria analyzed included distal motor latency of 4.4+ ms, distal sensory latency of 3.6+ ms, difference in median-ulnar mixed nerve palmar latency of 0.4+ ms, and CSA of the median nerve of 10+ mm². Median neuropathy was diagnosed in 235 hands, whereas 74 hands were found not to have median neuropathy. Overall, 141 hands (46%) had at least 1 of the 3 electrodiagnostic variables within 10% of the diagnostic cutoff values, and 137 hands (44%) had a median nerve CSA within 10% of 10 mm². By performing ultrasound in addition to NCS for each patient, an additional 65 hands (21%) had a definitive diagnosis on at least 1 of the 2 diagnostic modalities. Ultrasound and NCS yielded a similar number of patients within 10% of their diagnostic threshold values. When used together, the number of patients with a nonborderline diagnosis on at least 1 diagnostic modality was increased substantially.