Objective: The aim of the study was to investigate the associations of cross-sectional area (CSA) of the median nerve measured by ultrasonography, the median to ulnar nerve ratio (MUR), the median to ulnar nerve difference (MUD) and the ratio of CSA of the median nerve to height squared (MHS) in relation to electrodiagnostic classification of moderate and severe carpal tunnel syndrome (CTS) and thus to identify patients suitable for surgical treatment.
Materials and methods: A prospective study was conducted in patients aged ≥ 18 years who underwent both median and ulnar nerve ultrasonography and electrodiagnostic studies (EDS). 124 wrists of 62 patients were examined. The patients' characteristics were acquired through a questionnaire. CTS was diagnosed using EDS and classified according to the guidelines of the Czech Republic Association of Electrodiagnostic Medicine. The CSA of the median nerve and of the ulnar nerve were measured at the carpal tunnel inlet.
Results: Median nerve CSA at the tunnel inlet ≥ 12 mm2 correlates with electrodiagnostic classification of moderate to severe carpal tunnel syndrome. At this cut-off value, the sensitivity of ultrasonography is 82.4%, its specificity is 87.7%, the positive predictive value is 82.4%, the negative predictive value is 87.7%. MUD, MUR and MHS perform worse than the median nerve CSA, as shown by their lower area under the receiver operating characteristic curve.
Conclusions: Ultrasound could help us indicate surgical treatment for CTS, especially in patients with clinical findings. Our results suggest a cut-off value of CSA at the tunnel inlet of ≥ 12mm2.
Keywords: carpal tunnel syndrome; coss-sectional area; electrodiagnostic studies; median nerve; ultrasonography.