Pitfalls in using the ring finger test alone for the diagnosis of carpal tunnel syndrome

Impact of technical variations on the ring-finger test for carpal tunnel syndrome

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The median and ulnar nerves can be recorded consecutively or simultaneously to diagnose carpal tunnel syndrome.

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Simultaneous and consecutive recording of the median and ulnar nerves sensory latency have a poor agreement.

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Technical variations can have diagnostic consequences.

Objective

To assess if recording the sensory latencies of the median and ulnar nerves one-by-one (consecutive) or at the same time (simultaneous) in the ring-finger test for carpal tunnel syndrome (CTS) will show equivalent results or if it will lead to a different clinical classification of patients.

Methods

We assessed the limits of agreement between the simultaneous and the consecutive method based on the median- ulnar sensory latency difference derived by both methods in 80 subjects and compared the number of minimal CTS cases identified by the two methods.

Results

Limits of agreement ranged from −0.23 to 0.29 ms. A significantly higher proportion of subjects with minimal CTS (only detectable by using the comparison test) was found using the simultaneous method (n = 8 and 2, respectively; p = 0.03).

Conclusion

The two methods have a poor to moderate agreement as indicated by the range of the limits of agreement (0.5 ms).

Significance

Even small methodological changes to the ring-finger test can lead to results with different clinical meaning in the same individual and one should be aware of which method was used when interpreting results.

A handheld nerve conduction measuring device in carpal tunnel syndrome

OBJECTIVES

The diagnostic utility and reliability of an easy-to-operate novel handheld nerve conduction tester in carpal tunnel syndrome (CTS) were evaluated.

MATERIALS AND METHODS

Using the test device, the sensory nerve conductions (SNC) in the median and ulnar nerves were compared with each other in 194 patients with suspected CTS and 95 healthy controls. The test device results were compared with the results of nerve conduction studies (NCS) with traditional instrumentation.

RESULTS

The new device correctly classified 145 of the 149 hands (97.3%) without median nerve lesion and 171 of the 200 hands (85.5%) with median nerve lesions in traditional NCS. The specificity of the new tester compared with traditional instrumentation was 98%. The correlation coefficient for different technicians in different studies was 0.87.

CONCLUSIONS

The findings obtained with the new tester in CTS were reliable and reproducible. This tester may increase availability of NCS in CTS.

Effects of prolonged wrist flexion on transmission of sensory information in carpal tunnel syndrome

Carpal tunnel syndrome presents a constellation of symptoms which include discomfort (eg, pain, paraesthesia) and diminished sense of touch. This exploratory study simultaneously measured changes in tactile threshold and discomfort ratings during prolonged wrist flexion in symptomatic patients from a rehabilitation clinic and from a control population. Prolonged (15 min) wrist flexion significantly increased tactile threshold and discomfort ratings above baseline levels in both symptomatic and control populations. Sixty-two percent of the symptomatic sample was found to have abnormal conduction latency. Tactile threshold in symptomatic subjects with normal conduction latency (n = 13) did not differ significantly from control subjects (n = 36) at baseline but showed significant elevation during wrist flexion. In contrast, subjects with abnormal conduction latency (n = 21) exhibited significant elevation relative to control subjects at baseline and throughout wrist flexion as well as a slower recovery after flexion. Conduction latency correlated with baseline (r = .52, P < .0001) and 15-min (r = .67, P < .0001) tactile threshold for the entire subject population, as well as 15-min threshold (r = .53, P = .013) for the subpopulation with abnormal conduction latency. At 2.5 min after flexion, correlation was significant for whole (r = .64, P < .0001) and abnormal conduction latency (r = .58, P = .0063) samples. Regression slope of tactile threshold versus conduction latency was significantly greater than zero and did not differ significantly from linearity. The study demonstrates that increases in mechanosensory threshold and discomfort ratings during prolonged wrist flexion are more profound (and recovery less rapid) in patients with electrophysiologic evidence of injury.

PERSPECTIVE

This study demonstrates a provocative procedure that enhances the symptoms of carpal tunnel syndrome. This measure may help clinicians discriminate median nerve compression from other types of peripheral nerve injury and help researchers investigate the impact of mechanical stress, tissue compression, and vascular stasis on compression-related neuropathy.