Sensitive median-ulnar motor comparative techniques in carpal tunnel syndrome.

We describe two modified methods for median-to-ulnar motor conduction comparison 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-median 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 syndrome and electrophysiological evidence of median neuropathy at the wrist (based upon a prolonged median nerve palm-wrist latency), the diagnostic sensitivities were: 95-98%, 85-88%, and 75-78%, respectively. These tests are therefore highly sensitive. They are easily performed and require minimal additional effort to incorporate into commonly used clinical electrodiagnostic routines. They may be advantageous when a concomitant polyneuropathy is present, and they may also help avoid technical pitfalls and aid in identification of anatomic variants.