Dorsal Ulnar Cutaneous Nerve Conduction Study in Entrapment Ulnar Neuropathy at the Elbow

Objective: To evaluate the electrophysiologic findings of the dorsal ulnar cutaneous nerve (DUCN) in ulnar neuropathy at the elbow and to correlate the sensory nerve action potential (SNAP) amplitude of DUCN to those of ulnar compound muscle action potential (CMAP) and SNAP. Method: The subjects were 39 patients diagnosed as ulnar neuropathy at the elbow. Electrophysiologic classification consisted of 3 groups: conduction block (CB); conduction block and axonal degeneration (CBAD); axonal degeneration (AD). Findings of DUCN conduction study were evaluated according to the electrophysiologic classification. The amplitude of DUCN was correlated to those of CMAP and SNAP. Results: The DUCN conduction study was normal in all cases of CB (4 cases), but was abnormal in 21 cases of CBAD (23 cases) and in 10 cases of AD (12 cases). Even in the cases with AD, 4 cases showed normal DUCN potentials. Correlations of DUCN to ulnar SNAP and CMAP were r=0.48, (p＜0.01) and r=0.33, (p＜0.05), respectively. Conclusion: Findings of DUCN may be related to the fascicular involvement of the ulnar nerve at the elbow. Although it is possible for the DUCN to be spared in ulnar neuropathy at the elbow, electrophysiologic measurement of the DUCN response remains useful, but only in those cases where it is abnormal, which suggests the lesion to be at a more proximal site.