Sonographic Findings in the Ulnar Nerve According to the Electrophysiologic Stage of Carpal Tunnel Syndrome

Objectives Involvement of the ulnar nerve in patients with carpal tunnel syndrome is controversial. The aim of our study was to evaluate sonographic findings in the ulnar nerve in patients with carpal tunnel syndrome. Methods We performed median and ulnar nerve conduction studies with sonography in 109 hands of 60 patients with clinically suspected carpal tunnel syndrome. Sonographic findings were analyzed with regard to electrophysiologic stages of carpal tunnel syndrome. Results We found that the sensory conduction velocity of the ulnar nerve decreased as the electrophysiologic stage of carpal tunnel syndrome increased (P = .038), but there was no change in the cross‐sectional area of the ulnar nerve at the wrist. The median‐to‐ulnar nerve cross‐sectional area ratio at the wrist showed a significant correlation with the electrophysiologic stage of carpal tunnel syndrome (Spearman r = 0.431; P < .0001), in addition to the median nerve cross‐sectional area at the wrist and the wrist‐to‐ forearm median nerve cross‐sectional area ratio. Conclusions In our study, ulnar nerve involvement in patients with carpal tunnel syndrome was shown electrophysiologically but not sonographically. These results suggest that morphologic changes in the ulnar nerve do not occur in carpal tunnel syndrome, although functional changes may occur.