Science News: Assessing Diagnostic and Severity Grading Accuracy of Ultrasound Measurements for Carpal Tunnel Syndrome Compared to Electrodiagnostics

Submitted by: Rebecca O’Bryan, MD

Edited by: Niranjan Singh, MD

Chen YT, Miller Olson EK, Lee SH, Sainani K, Fredericson M. Assessing diagnostic and severity grading cccuracy of ultrasound measurements for carpal tunnel syndrome compared to electrodiagnostics. PM R. 2021;13(8):852-861. doi:10.1002/pmrj.12533

Summary: This is a prospective study of 95 18 to 80-year-old patients referred for electrodiagnostic (EDX) testing of idiopathic carpal tunnel syndrome (CTS). Exclusion criteria for prior CTS and other concomitant confounding factors. The combined sensory index (CSI) and Bland criteria were used to assess for severity. Bland severity grading was determined as follows: Grade 0 had no neurophysiological abnormality, Grade 1- very mild CTS with the only abnormalities identified on comparison or inching tests, Grade 2- mild CTS with decreased median sensory conduction velocity < 40 m/s, Grade 3- moderate CTS with motor compound muscle action potential (CMAP) latency >4.5 ms, Grade 4- severe CTS with absent sensory nerve action potential (SNAP), Grade 5- very severe CTS with motor latency >6.5 ms, and Grade 6- extremely severe CTS with motor CMAP amplitude <0.2 mV. The median nerve cross-sectional area (CSA) was measured at four locations: the distal forearm at the level of the pronator quadratus (CSA-PQ), the carpal tunnel inlet at the level of the pisiform (CSA-Inlet), the carpal tunnel outlet at the level of the hook of the hamate (CSA-Outlet), and within the carpal tunnel at the point of maximum CSA (CSA-Tunnel) by each examiner independently. The change (∆) in CSA was calculated by subtracting the CSA-PQ from each of the three carpal tunnel measurements to derive ∆Inlet, ∆Outlet, and ∆Tunnel. The wrist to forearm (WFR)-Inlet, WFR-Outlet, and WFR-Tunnel were then each calculated using the CSA at each of the three carpal tunnel locations divided by CSA-PQ. All ultrasound (US) measurements had high diagnostic accuracy for CTS, but had poor concordance with severity via the Bland criteria and CSI severity grades. Age stratification did not improve concordance. ∆CSA had the highest diagnostic accuracy

Comments: This was a very interesting article, as this is currently the largest study to my knowledge investigating the diagnostic utility of EDX vs US for the diagnosis of CTS. While US once again appears to be an excellent tool for the screening/diagnosis of CTS, this study does not support the use of US measurements for diagnostic severity. It is important to note that CSI (the most sensitive tool in EDX for CTS dx) was used. Based on this study, EDX continues to hold clinical relevance alongside US for staging of CTS which can help guide clinical management.