Median nerve stiffness measurement by shear wave elastography: a potential sonographic method in the diagnosis of carpal tunnel syndrome.

OBJECTIVES: To measure the median nerve (MN) stiffness by quantitative shear wave elastography (SWE) at the carpal tunnel inlet and to determine whether SWE can be used in the diagnosis of carpal tunnel syndrome (CTS).

METHODS: The study included 37 consecutive patients (60 wrists) with a definitive diagnosis of CTS and 18 healthy volunteers (36 wrists). The MN cross-sectional area (CSA) by ultrasound and stiffness by SWE were studied. The difference between CTS patients and controls, and the difference among subgroups based on electrodiagnostic tests were studied by the Student's t test. Interobserver variability and ROC analysis were performed.

RESULTS: The MN stiffness was significantly higher in the CTS group (66.7 kPa) when compared to controls (32.0 kPa) (P < 0.001), and higher in the severe or extreme severity group (101.4 kPa) than the mild or moderate severity group (55.1 kPa) (P < 0.001). A 40.4-kPa cut-off value on SWE revealed sensitivity, specificity, PPV, NPV and accuracy of 93.3%, 88.9%, 93.3%, 88.9% and 91.7%, respectively. Interobserver agreement was excellent for SWE measurements.

CONCLUSIONS: Median nerve stiffness at the carpal tunnel inlet is significantly higher in patients with carpal tunnel syndrome, for whom shear wave elastography appears to be a highly reproducible diagnostic technique.

KEY POINTS: • Clinical examination is important for diagnosis of carpal tunnel syndrome • Shear wave elastography (SWE) offers new clinical opportunities within diagnostic ultrasound • SWE is highly reproducible in evaluation of median nerve stiffness • Median nerve stiffness is significantly increased in carpal tunnel syndrome • Elastography could become useful in diagnosis of carpal tunnel syndrome.