Two U-M physicians performed the tests. In the first round, each physician tested both wrists of each subject. In the second round, three weeks later, tests were performed by one of the physicians in the dominant wrist only.
The examiners tested two nerves for abnormalities: the median nerve, which runs down the middle of the arm and wrist and controls the palm, the thumb, and several fingers; and the ulnar nerve, which runs through the outer arm and wrist to control the back of the hand and the small and ring fingers.
The median nerve is more affected by carpal tunnel syndrome, in which overuse of the hand and wrist causes tissue swelling. This, in turn, narrows the gap between the carpal, or wrist, bones and ligaments through which the nerve runs, causing pressure on the nerve. Women between ages 30 and 60 are most commonly affected.
Although a variety of tests can detect conditions like carpal tunnel syndrome, nerve conduction studies have been used as the gold standard. The test uses a small jolt of electricity to stimulate each nerve, then measures the time it takes for the stimulus to reach the muscle. A second stimulation of the same nerve at a different spot, or of the other major nerve, allows the lag time, known as the latency, to be compared. This lets doctors spot the existence and the extent of nerve damage in different locations.
In the U-M study, the results recorded by each examiner for each patient were compared, as were each examiner's results from both their exams of the workers. In both cases, results showed that certain tests were better than others. Both between examiners and within the same examiner, median nerve tests were more reliable than ulnar nerve tests.
A key question was how differences between examiners would affect a diagnosis of carpal tunnel syndrome. That is, would the first examiner rate a test r
Contact: Kara Gavin
University of Michigan Health System