Correlating Ultrasound Echogenicity of the Abductor Pollicis Brevis and Median Nerve Cross-Sectional Area in the Setting Carpal Tunnel Syndrome: A Pilot Study.

INTRODUCTION

Carpal tunnel syndrome is the most common peripheral entrapment neuropathy, often associated with structural and functional changes in the median nerve and thenar muscles. Neuromuscular ultrasound is increasingly used to complement nerve conduction studies in carpal tunnel syndrome evaluation, yet its potential for assessing muscle integrity remains underexplored. This pilot study examined correlations between median nerve cross-sectional area (MNCSA) and abductor pollicis brevis (APB) muscle characteristics on ultrasound.

METHODS

Veterans were enrolled at the Clement J. Zablocki VA Medical Center from July to November 2023. Inclusion criteria were age ≥18 years, carpal tunnel syndrome confirmed by nerve conduction studies, and planned carpal tunnel release. Exclusion criteria included prior carpal tunnel release, upper limb trauma or surgery, hand deformities, peripheral neuropathy, and diabetes. Ultrasound images of the median nerve and APB were obtained. Using Adobe Photoshop, APB echogenicity (grayscale value, black/white ratio) and cross-sectional area in longitudinal and transverse views were calculated and analyzed for correlation with MNCSA.

RESULTS

Ten participants were included. Strong negative correlations were observed between MNCSA and APB cross-sectional area in longitudinal and transverse views (Pearson coefficients, -0.51 and -0.50, respectively). Weak to moderate positive associations were found between MNCSA and APB echogenicity values (0.32 and 0.24, respectively).

CONCLUSIONS

APB characteristics on ultrasound, including echogenicity and cross-sectional area, may serve as complementary indicators of carpal tunnel syndrome. Future research should include larger samples, control groups, and assessment of correlations with carpal tunnel syndrome severity on nerve conduction studies.