PROVOCATIVE MOTOR-NERVE CONDUCTION TESTING IN PRESUMPTIVE CARPAL-TUNNEL SYNDROME UNCONFIRMED BY TRADITIONAL ELECTRODIAGNOSTIC TESTING

In this controlled prospective study 22 consecutive surgical candidate s with clinically diagnosed CTS and negative findings:on median nerve- sensory and motor-conduction velocity tests in both hands were reexami ned with a protocol incorporating 5 specific positions of the wrist. F our of the 5 positions represented maximum physiologic ranges of motio n for the patient. These positions were neutral (unstressed), extensio n, flexion, radial deviation, and ulnar deviation. Motor latency was r ecorded in each of the 5 positions using otherwise standard technique. The least latency value in the test sequence was subtracted from the greatest to yield a value called-differential latency. Thirty-two cont rol studies were obtained on both hands of 16 normal volunteers and we re used to establish a control differential latency which was seen to have a mean of .13 ms. A 2 standard deviation z value of .11 ms was ca lculated, giving an upper limit of normal (control) differential laten cy of .24 ms. Preoperative studies yielded an average differential lat ency of .44 ms; with 26 of 22 patients having differential latency val ues of greater than .24 ms. Evaluations of these same patients 3 month s after surgery showed differential latency values within the same ran ge as those of the control group. Simple modification bf standard nerv e testing techniques to include positional variation increased the yie ld of positive lest results in 20 of 22 patients with CTS whose electr odiagnostic tests otherwise produced negative findings.