Abstract
BackgroundWe have previously proposed that sensory nerve conduction (SNC) in the median nerve should be classed as abnormal when the difference between conduction velocities in the little and index fingers is > 8 m/s. In a prospective longitudinal study, we investigated whether this case definition distinguished patients who were more likely to benefit from surgical treatment.MethodsWe followed up 394 patients (response rate 56%), who were investigated by a neurophysiology service for suspected carpal tunnel syndrome. Information about symptoms, treatment and other possible determinants of outcome was obtained through questionnaires at baseline and after follow-up for a mean of 19.2 months. Analysis focused on 656 hands with numbness, tingling or pain at baseline. Associations of surgical treatment with resolution of symptoms were assessed by Poisson regression, and summarised by prevalence rate ratios (PRRs) and associated 95% confidence intervals (95% CIs).ResultsDuring follow-up, 154 hands (23%) were treated surgically, and sensory symptoms resolved in 241 hands (37%). In hands with abnormal median SNC, surgery was associated with resolution of numbness, tingling and pain (PRR 1.5, 95% CI 1.0-2.2), and of numbness and tingling specifically (PRR 1.8, 95% CI 1.3-2.6). In contrast, no association was apparent for either outcome when median SNC was classed as normal.ConclusionsOur definition of abnormal median SNC distinguished a subset of patients who appeared to benefit from surgical treatment. This predictive capacity gives further support to its validity as a diagnostic criterion in epidemiological research.
Highlights
We have previously proposed that sensory nerve conduction (SNC) in the median nerve should be classed as abnormal when the difference between conduction velocities in the little and index fingers is > 8 m/s
We recently examined the relationship of median SNC to symptoms and signs in a consecutive series of patients, who were being investigated for suspected carpal tunnel syndrome (CTS) at a general hospital [2]
The clearest discrimination from normal hands was achieved with a cut-point of 8 m/s for the difference between little and index finger SNC velocities, and on this basis, we proposed that with the method of testing employed, a value of > 8 m/s was a reasonable definition for an abnormal difference between SNC velocities in the little and index fingers
Summary
We have previously proposed that sensory nerve conduction (SNC) in the median nerve should be classed as abnormal when the difference between conduction velocities in the little and index fingers is > 8 m/s. Demonstration of impaired distal sensory nerve conduction (SNC) in the median as compared with the ulnar or radial nerve is generally regarded as the most sensitive neurophysiological marker for the disorder [1]. We recently examined the relationship of median SNC to symptoms and signs in a consecutive series of patients, who were being investigated for suspected CTS at a general hospital [2]. The clearest discrimination from normal hands was achieved with a cut-point of 8 m/s for the difference between little and index finger SNC velocities, and on this basis, we proposed that with the method of testing employed, a value of > 8 m/s was a reasonable definition for an abnormal difference between SNC velocities in the little and index fingers (this would include hands in which no signal could be detected when the index finger was tested, indicating extreme impairment of conduction)
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