The Utility of Semmes-Weinstein Monofilament Test in Detecting Carpal Tunnel Syndrome with Clinical Stage, Nerve Conduction Study, and Sonography Correlations

Abstract

Background and purpose: Nerve conduction study (NCS) and ultrasonography (US) are used to support the diagnosis of carpal tunnel syndrome (CTS). The ability of the Semmes-Weinstein monofilament test (SWMT), a sensibility threshold test, to detect CTS, and its relationship to clinical severity, NCS, and US, remain controversial. We conducted this study to address this controversy. Method: Thirty-three patients presenting with typical symptoms and signs of CTS and 20 normal subjects were enrolled. SWMT on the index finger, NCS, and US of the cross-sectional area of the median nerve at the pisiform level (PCSA) were performed. Receiver operating characteristic (ROC) curves of SWMT, variables of NCS, and PCSA were plotted to analyze their discriminative utilities. The diagnostic agreement for CTS among SWMT, NCS, and PCSA were analyzed by kappa statistics. Sensitivities, specificities, positive predictive values (PPV), negative predictive values (NPV), and accuracies, as well as the correlation coefficients among SWMT, NCS measures, and PCSA, were calculated. Results: The areas under the ROC curve (AUC) for SWMT and PCSA were 0.852 and 0.71, respectively. AUCs for three NCS variables ranged from 0.822 to 0.902. All these variables were discriminative for CTS and were not significantly different in their discriminative power. SWMT yielded sensitivity, specificity, PPV, NPV, and accuracy of 82%, 70%, 82%, 70%, and 77%, respectively. There is significant agreement in detection of CTS using SWMT and NCS (kappa=0.575, p＜0.001). The kappas between SWMT and PCSA, as well as NCS and PCSA, were 0.305 and 0.427, respectively (p=0.025 and 0.002). SWMT significantly correlates with not only clinical stage, but also NCS measures and PCSA (r ranged from 0.381 to 0.581, p＜0.01). Conclusion: SWMT shows discriminative power similar to NCS and US for detection of CTS. SWMT also has a moderate correlation with clinical stage, NCS measures, and PCSA on US. As a painless, convenient, and inexpensive modality, SWMT may have the ability to diagnose CTS, but further research is needed.