Comparison of Borderline Ultrasound and Nerve Conduction Studies for Carpal Tunnel Syndrome
Cory J Demino, MD, University of Pittsburgh School of Medicine, Pittsburgh, PA and John R Fowler, MD, UPMC, Pittsburgh, PA
Choosing cut-off 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.
Materials & Methods
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 DML of 4.4+ ms, DSL 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 while 74 hands were found not to have median neuropathy. Overall, 141 hands (46%) had at least one of the three electrodiagnostic variables within 10% of the diagnostic cut-off values and 137 hands (44%) had a median nerve CSA within 10% of 10mm2. By performing ultrasound in addition to NCS for each patient, an additional 65 hands (21%) had a definitive diagnosis on at least one of the two 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 non-borderline diagnosis on at least one diagnostic modality was increased substantially.
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