Diagnostic validity of ultrasonography in carpal tunnel syndrome

Introduction. Ultrasonography has emerged as an alternative tool for diagnosing peripheral neuropathies, such as carpal tunnel syndrome (CTS). Yet, data are still lacking as regards the diagnostic validity of the different ultrasonography measurements for detecting CTS in clinical settings. Aims. To determine the diagnostic validity of ultrasound measurements of the cross-sectional area of the median nerve in the wrist (CSA-M) and of the ratio of the area of the median nerve between the wrist and the forearm (R-WF) in the diagnosis of CTS, using electroneuromyography (ENG) as the reference technique. Patients and methods. Ultrasound measurements were performed on 59 subjects (100 wrists) who were referred to have an ENG due to suspected CTS. The examiners that performed the ultrasonography scan did not know the results of the ENG. The cut-off points were later calculated by means of ROC curves for each of the measurements (CSA-M and R-WF) and their diagnostic validity was analysed. Results. With a cut-off point of 9.15 mm(2), CSA-M measurement obtained a sensitivity of 75.81%, a specificity of 74.29%, a positive likelihood ratio of 2.95 and a negative likelihood ratio of 0.33. For the R-WF measurement and a cut-off point of 1.56, the values for sensitivity, specificity, and positive and negative likelihood ratios were 70.97%, 71.43%, 2.48 and 0.4, respectively. Conclusions. Both the CSA-M and R-WF appear to be useful measures in the diagnosis of CTS, taking the ENG as a reference test.