Table 6.

Electrodiagnostic techniques and reference values for diagnosing carpal tunnel syndrome.

	Stimulation site	Recording site	Reference values
Sensory nerve action potential
Median nerve	4 cm proximal to the recording site	2nd digit	Onset latency: ≤ 3.5 ms and peak to peak amplitude: ≥ 20 µV
Transcarpal latency	7 and 14 cm proximal to the recording site, respectively	2nd digit	Difference of onset latency between two stimulations: < 1.7 ms
Ring finger	Median and ulnar nerves at wrist, respectively, 14 cm proximal to the recording site	4th digit	Difference of onset latency between median and ulnar nerves: < 0.6 ms
Compound motor nerve action potential
Median nerve	8 cm proximal to APB muscle	APB muscle	Onset latency: ≤ 4.0 ms and peak to peak amplitude: ≥ 5 mV
Lumbrical/Interossei	Median and ulnar nerves at wrist, respectively	Midpoint of 3rd metacarpal bone	Difference of onset latency between two stimulations: ≤ 0.4 ms

APB, abductor pollicis brevis muscle.