Using Mixed Latency Difference to Diagnose Mild Ulnar Nerve Problems

Ulnar and median nerve impulses across the elbow are difficult to test. The nerves don't always run straight. They curve and sometimes slip out of the shallow groove designed for them. In this study scientists try a different way of measuring the function of these two nerves.

They used a simple and fast method called mixed latency difference (MLD). MLD is the difference between the peak action potential of the median nerve compared to the ulnar nerve. The action potential is a wave of electrical discharge that travels along the nerve. It measures latency or how fast the nerve carries messages.

In this study the nerves were stimulated at the wrist, below the elbow, and above the elbow. MLD was measured in 57 normal, healthy adults who had no signs or symptoms of nerve problems. They tested another group of 100 patients who had positive symptoms of ulnar nerve problems. This second group was divided into two groups.

One group included patients who had a test positive for ulnar nerve neuropathy of the elbow (UNE). The second group had "suspected" UNE. They called it suspected because the standard test (motor conduction velocity) wasn't positive to prove change in the nerve function.

Results showed that MLD seems to be linked with height. This is a new finding never reported before. The authors aren't sure how to explain this correlation. They say it could be greater height means a longer nerve length and longer nerve conduction time. Or maybe with increased height, there's less difference between the two nerves.

Overall this study showed that MLD is a good way to test for mild cases of UNE. The test avoids measuring nerve function across the elbow where problems develop. It's less accurate with severe cases of ulnar nerve injury.

References: Carlos O. Heise, MD, and Sonia M. Toledo, MD. Mixed Latency Difference for Diagnosis of Ulnar Neuropathy at the Elbow. In Archives of Physical Medicine and Rehabilitation. March 2006. Vol. 87. No. 3. Pp. 408-410.