Subclinical Distal Ulnar Nerve Involvement in Carpal Tunnel Syndrome: Electrophysiological Evidences from Calculated Indexes

J Korean Assoc EMG Electrodiagn Med 2006;8(1):26-32.
Published online May 10, 2006.

Abstract

Objectives: Ulnar nerve lesions associated with carpal tunnel syndrome (CTS) has received little attention. Clinical and experimental studies has argued that entrapment of median nerve at the carpal tunnel could affect the ulnar nerve in the Guyon canal by the same process of CTS. The purpose of this study is to identify ulnar nerve lesions associated with CTS, especially in the subclinical cases. Methods: Nerve conduction study of upper limbs was investigated in 61 unilateral CTS (group I), 63 bilateral CTS (group II) and 53 normal controls. To measure the distal nerve dysfunction of ulnar and median nerves, residual latency (RL), terminal latency index (TLI) and modified F raito (MFR) were calculated in both nerves. The results were compared among groups. Results: Compared with controls, DML, RL, and TLI of median and ulnar nerves were significantly different among groups (ANOVA p < 0.01). Group II showed more significant changes in ulnar nerves than group I, which indicated ulnar nerves were damaged more in bilateral CTS. The indexes used in this study were correlated in the control group, which were not in both group I and II. Conclusion: These findings support the presence of subclinical focal lesion of distal ulnar nerve rather than subclinical ulnar involvement as a part of generalized neuropathy. The pathogenesis of ulnar involvement in CTS remains to be elucidated.

Key Words: Carpal Tunnel Syndrome, Ulnar Neuropathies, Neural Conduction, Calculated Indexes