Ultrasound May Diagnose Ulnar Neuropathy Despite Normal Electrodiagnostic Findings

Most people know someone with or has heard of carpal tunnel syndrome, a repetitive stress injury involving the nerve that goes through the wrist (the carpal tunnel) and into the hand. While this is the most common entrapment neuropathy (nerve problem due to a nerve being trapped or pressed on), the second most common entrapment neuropathy that involves the arm has to do with the elbow and how the nerve passes through the cubital tunnel. This is called ulnar neuropathy.

When a person has entrapment neuropathy from compression of the nerve in the cubital tunnel, this can leave them with weakness in the fourth and fifth fingers (the ring and little fingers). They may also experience problems with the forearm muscles that are fed by the ulnar nerve, the one affected by this problem. The neuropathy is diagnosed by doctors using electrodiagnosis, tests that use electricity to assess how the muscles respond. Usually, the sensitivity of diagnosing an elbow problem is lower than that of testing for the wrist. In fact, there are reports of patients who have supposedly normal results from the electrodiagnostic tests but they still have the signs and symptoms of ulnar neuropathy.

There are some theories that suggest why some patients' neuropathy isn't diagnosed with electrodiagnosis. These theories include issues such as improper positioning of the elbow during testing or the problem being too mild still to be detected. Some doctors have begun using high-resolution ultrasound to determine if there are nerve conduction issues in some neuromuscular disorders and some studies have looked into the usefulness of this type of ultrasound to look for entrapment problems. The authors of this study evaluated ultrasound and nerve abnormalities in four patients who had undergone typical electrodiagnosis that didn't find any problems, yet the patients still had the signs and symptoms of an entrapment.

After the patients underwent the initial testing, they underwent ultrasound testing that checked all along the ulnar nerve from the wrist up to the underarm. In the first case, a 50-year-old woman who had experienced numbness for several months, as well as decreased feeling in the fourth and fifth fingers, the ultrasounds showed a marked enlargement of the ulnar nerve about 1 centimeter away from the nerve, next to the top of the forearm.

The second case involved a 56-year-old manual laborer who also had numbness in the fourth and fifth finger, but it had been present for several years. the ultrasound findings showed an enlargement of the ulnar nerve, also near the top of the forearm. The third patient, a 28-year-old woman complained of similar finger numbness, which began two months earlier after a marathon session of playing video games while resting her elbow on a hard surface. Once again, the ultrasound showed an area above the forearm, as it also did for the fourth patient, a 30-year-old man who has a high level of computer use and who had experienced similar numbness for three months.

The authors wrote that this was the first study done to determine suspected ulnar neuropathy, despite supposedly normal electrodiagnostic findings, although there has been an earlier study that investigated nerve changes in ulnar neuropathy in patients who appeared to have the problem but were not diagnosed by electrodiagnosis. They concluded that more research should be done into using ultrasounds to help diagnosis of patients who appear to have ulnar neuropathy but do not have electrodiagnostic proof of it.

References: Joon Shik Yoon, MD, PhD, Francis O. Walker, MD, and Michael Cartwright, MD. Ulnar Neuropathy With Normal Electrodiagnosis and Abnormal Nerve Ultrasound. In Archives of Physical Medicine & Rehabilitation. February 2010. Vol. 91. No. 2. Pp. 318-320.