Sensitive median-ulnar motor comparative techniques in carpal tunnel syndrome

We describe two modified methods for median-to-ulnar motor conduction compa rison in the diagnosis of median neuropathy at the wrist: the median-thenar to ulnar-thenar latency difference (TTLD), and the median-thenar to ulnar- hypothenar latency difference (THLD). We also describe an F-wave ulnar-to-m edian comparative test, the F-wave latency difference (FWLD). The abnormal cutoffs based upon 34 normal controls are: TTLD, 0.8 ms; THLD, 1.2 ms; FWLD , 0.6 ms. In 50 patients (79 hands) with clinically defined carpal tunnel s yndrome and electrophysiological evidence of median neuropathy at the wrist (based upon a prolonged median nerve palm-wrist latency), the diagnostic s ensitivities were: 95-98%, 85-88%, and 75-78%, respectively. These tests ar e therefore highly sensitive. They are easily performed and require minimal additional effort to incorporate into commonly used clinical electrodiagno stic routines. They may be advantageous when a concomitant polyneuropathy i s present, and they may also help avoid technical pitfalls and aid in ident ification of anatomic variants. (C) 1999 John Wiley & Sons, Inc.