High-resolution ultrasound findings of the median nerve in electrophysiologically severe carpal tunnel syndrome

Abstract

Objective: Carpal tunnel syndrome (CTS) is caused by entrapment of the median nerve at the wrist. Nerve conduction studies (NCS) confirm the diagnosis and grade the severity. High-resolution ultrasound (HRUS) is useful for diagnosing CTS and excluding alternative etiologies. However, data on sonological characteristics of electrophysiologically severe CTS are limited. We aim to describe the sonological characteristics of patients with severe CTS.

Methods: Fifty-two adults fulfilling the American Association of Neuromuscular and Electrodiagnostic Medicine practice parameters for the diagnosis of CTS and absent median nerve sensory action potential (severe CTS) were included. Cross-sectional areas (CSA) of the median nerve were obtained at the level of the carpal tunnel inlet and mid-forearm. The wrist-to-forearm ratio (WFR) was calculated. These findings were compared with 60 age- and gender-matched healthy controls.

Results: In the patient group, the mean median nerve CSAs (in mm2) at the wrist and forearm and WFR were 15.64±3.7, 5.53±0.7 and 2.86±0.7 respectively, while in the control group, these were 7.50±0.9, 4.91±0.7 and 1.56±0.3 respectively. All parameters were significantly higher in patients compared to controls. A threshold value of 10.45 mm2 for median nerve CSA at the wrist showed a high accuracy for severe CTS. A threshold value of WFR of 2.07 showed high sensitivity and specificity of 94.2% and 98.3%, respectively.

Conclusion: The present study provides robust data on the sonological characteristics of severe CTS. HRUS being a non-invasive tool, can be used to identify severe CTS at the point of care.