Comparison of sensory conduction techniques in the diagnosis of mild idiopathic carpal tunnel syndrome: which finger, which test?

To compare the sensitivity of different electrodiagnostic tests on the same hand affected by mild carpal tunnel syndrome (CTS), 189 hands with the clinical diagnosis of CTS and 61 hands of healthy persons were evaluated prospectively. On all hands, median sensory studies from digits 1, 2, 3, 4, and the palm-to-wrist segment from digit 3 and medial motor latency were recorded. Sixty-two hands with delayed motor latency (>4.2 ms) were excluded to ensure that only mild cases were enrolled. Sensory median-radial latency differences from the thumb, median-ulnar latency difference between second and fifth digits, and median-ulnar latency difference from the fourth digit were calculated in each limb. Sensory studies of only one median innervated digit failed to diagnose 15-20% of hands. Conduction velocity at the palm-to-wrist segment was the most sensitive, diagnosing 99% of cases. In comparative tests, median radial sensory latency difference from the first digit was the most sensitive (94%), and median ulnar latency difference from the fourth digit was the least (85%) sensitive. Segmental measurement has the highest diagnostic yield and may be used first in the evaluation of CTS.