Ultrasound: A Screening Tool for Carpal Tunnel Syndrome

Abstract

Background Electrodiagnostic test is considered as the gold standard for diagnosis of carpal tunnel syndrome (CTS). Ultrasonography provides a simple non-invasive means of visualising peripheral nerve pathology. Objective The objective of the study was to assess the role of ultrasonography in CTS and its correlation with the present day gold standard of nerve conduction studies (NCS). Materials and Methods A prospective cohort size of 100 subjects was calculated based on a hypothesized sensitivity of 90% and a confidence interval of 85-95%. All 100 subjects, 64 controls and 36 patients underwent nerve conduction studies and USG. Transverse images of the median nerve were obtained at three levels: proximal to the carpal tunnel inlet, at the carpal tunnel inlet and at the carpal tunnel outlet. The flattening ratio was also assessed at the tunnel inlet and outlet. Statistical analysis was done to corelate the ultrasound findings at each level with nerve conduction studies and calculation of the positive and negative predictive values. The cut offs of the cross-sectional areas of the median nerve at the three anatomical levels on ultrasonography were taken at the best sensitivity and specificity according to the ROC curve. Results We found that at any one anatomical level, the sensitivity of ultrasound to detect carpal tunnel syndrome by increase in the cross-sectional area of median nerve as compared to the nerve conduction studies is 90%. Conclusions At 45% specificity, ultrasonography could be used as a non-invasive and easily available screening tool in carpal tunnel syndrome. Also, the best level to look for nerve compression is at the level of the carpal tunnel inlet.