Electrodiagnosis of mild carpal tunnel syndrome.

Electrophysiologic tests have been reported to detect mild carpal tunnel syndrome (CTS). Such tests include (i) absolute palmar latency of median wrist segment; (ii) comparison of median and radial distal sensory latencies in digit I; (iii) comparison of median and ulnar distal sensory latencies in digit IV; (iv) comparison of median and ulnar palmar latencies; (v) comparison of median and ulnar sensory potential amplitudes in digits II and V. To clarify the clinical utility of these tests, the parameters of all five tests were determined across four carefully established patient subgroups: group A, controls; group B, CTS referrals with normal nerve conduction studies (NCS) and normal needle electromyography (EMG); group C, CTS referrals with abnormal NCS and normal EMG; group D, CTS referrals with abnormal NCS and abnormal EMG. Special attention was focused on patients in group B who represent the diagnostic dilemma. In group B, tests ii and iii each yielded abnormal results in 44% of hands, while the combination of tests ii and iii yielded abnormal results in 51% of hands.