Characterization of Carpal Tunnel Syndrome using High Frequency Ultrasound Imaging: a Comparison of Ultrasonic Features in the Median Nerve

Diagnosis of Carpal Tunnel Syndrome (CTS) is based on the medical history, clinical provocation test, and electrodiagnostic studies. However, electrodiagnostic studies can be uncomfortable for some patients, due to the invasiveness. Ultrasonography has been suggested to characterize the median nerve (MN) in patients with CTS as an aid in the initial assessment. The study aimed to compare the diagnostic performance of ultrasonic features from the MN in normal volunteers and patients with CTS using high frequency ultrasound. All participants were examined in the sitting position with a palm facing up using an Aplio i800 system (Cannon Medical Systems, Otawara, Japan). The cross-sectional area (CSA; in mm2) and blood flow of MN were evaluated at the wrist using an i24LX8 probe (9-24 MHz). Blood flow was interrogated using Color Doppler Imaging, Power Doppler Imaging, Monochrome Superb Microvascular Imaging (mSMI), and Color Superb Microvascular Imaging with the same imaging settings for all participants. The maximum vascular area from each technique was quantified offline using Matlab (MathWorks, Natick, MA, USA). Shear wave elastography (SWE) images were acquired using the i18LX5 probe (4-18 MHz) at the wrist. The stiffness (in kPa) of the MN was quantified using a built-in software tool. To date, analysis included 20 hands in 10 normal volunteers and 14 hands in 9 patients with CTS. The CSA, vascular area, and stiffness of MN in patients with CTS were significantly different from those in normal volunteers (p < 0.04). The CSA, vascularity from mSMI, and stiffness showed high diagnostic performance independently, albeit based on a small sample size. Additionally, the combination of CSA, mSMI, and stiffness of SWE showed a specificity of 100% and a sensitivity of 93% with an overall accuracy of 95%.