Correlating nerve conduction studies and clinical outcome measures on carpal tunnel syndrome: lessons from a randomized controlled trial.

The reported relationships between nerve conduction studies (NCS) and outcome measures in carpal tunnel syndrome (CTS) are weak to moderate. However, selection of patients may have confounded nonrandomized studies. NCS have potentially great value in selecting patients for a specific treatment and in objectively assessing the efficacy of treatments in CTS, especially if they correlate significantly with clinical outcome measures. To investigate the relationship between clinical outcome measures for the severity of complaints and NCS in patients treated for CTS, data were obtained from a multicenter randomized controlled trial on the efficacy of splinting versus surgery for CTS. At baseline and 12 months after randomization, clinical outcome measures were assessed and NCS were performed. In total, 138 patients completed the questionnaires and underwent repeated NCS. Relationships were analyzed with Spearman rank correlation coefficients and Pearson correlation coefficients. All NCS parameters showed highly significant improvement compared with baseline (P < 0.001). Modest correlations (< 0.4) were found between the neurophysiologic and clinical outcome measures after 12 months, and between the changes in these different categories of outcome measures. This study confirms that the parameters of NCS improve significantly after treatment for CTS, but the modest correlations between neurophysiologic and clinical outcome measures do not support that NCS are routinely performed in clinical practice to evaluate treatment effects. However, studies investigating the effects of treatment for CTS should incorporate both clinical outcome measures and NCS, because they are complementary. Furthermore, NCS can provide additional information to the clinician when treatment effects are unsatisfactory.