Mixed latency difference for diagnosis of ulnar neuropathy at the elbow

To provide reference values and to compare this technique with the standard motor conduction velocity (MCV) of the ulnar nerve.

Retrospective unmasked study.

Private and institutional practice.

The reference group included 57 healthy volunteers. Patients included 100 subjects with suspected ulnar neuropathy at the elbow (UNE) referred for neurophysiologic evaluation. This group was subdivided into 2 groups: group A was composed of 45 patients with UNE confirmed by MCV of the ulnar nerve, and group B included 55 patients with suspected UNE in whom the diagnosis could not be established by MCV of the ulnar nerve.

Not applicable.

Differences between peak latencies of ulnar and median mixed nerve action potentials at the arm, after stimulating these nerves at the wrist. This was called mixed latency difference.

The upper normative limit of the mixed latency difference was 1.1 ms, and there was a significant correlation with height. In group A, the mixed latency difference was abnormal in 80% of the cases and could not be calculated in 18%. In group B, the mixed latency difference was abnormal in 8 (15%) patients. All of these had abnormal "inching" of the ulnar nerve across the elbow.

The mixed latency difference was particularly useful in cases of mild UNE.