Mega Nerves: Factors Associated with Large Median Nerves on Ultrasound of the Carpal Tunnel

Abstract

Background: Although increased cross-sectional area of the median nerve on ultrasound has been associated with carpal tunnel syndrome, there has been little research examining outlier cases with exceedingly large nerves. The purpose of this study was to identify factors associated with these “mega” nerves, and to determine whether these nerves carry with them increased severity of disease. Methods: Patients who presented to clinic with upper extremity paresthesias over a 4-year period were included in this study. Two groups were created: mega nerves (cross-sectional area >2 SD above average), and nonmega nerves. Statistical analysis was performed to compare demographics, symptom scores, and nerve conduction studies (NCS). Significant variables were then compared between patients with mega nerves and those with ultrasound positive nerves (≥10 mm2), which did not reach mega size (normal nerves were excluded). Results: The cohort included 425 median nerves with 25 mega nerves. The groups differed significantly in diabetes status, body mass index (BMI), Boston Carpal Tunnel Questionnaire (BCTQ) Symptom Severity Scale scores, and NCS results. When compared only with ultrasound positive but nonmega nerves, mega nerves were still associated with diabetes, higher BMI, and worse NCS results. Conclusions: Diabetes, BMI, NCS results, and BCTQ Symptom Severity Scale scores are associated with mega nerves. However, BCTQ scores do not differ between mega nerves and other ultrasound positive nerves. In patients with obesity or diabetes, outlier ultrasound measurements may not correlate with worsened clinical symptoms, even in the setting of more significantly altered NCS results.