Reply to Letter to the Editor: The Sensitivity and Specificity of Ultrasound for the Diagnosis of Carpal Tunnel Syndrome: A Meta-analysis

We thank Descatha et al. for their interest in our article [3] and their comments. A systematic review and meta-analysis uses a systematic approach to identify evidence from multiple studies to attain an accurate and unbiased estimate of the association between interventions or exposures and events that could be widely applicable to a larger population [4]. By combining patient data from multiple studies appropriately, meta-analyses allow for larger sample sizes and therefore statistical power to determine treatment effects [1, 4]. However, systematic reviews are not without limitations. All reviews are retrospective and observational and therefore are subject to random error and systematic bias [1]. Systematic reviews, when conducted properly, can provide a high level of evidence, improve the precision of the analysis by increasing the sample size, and help to explain differences in study results attributable to heterogeneity [2]. Ultimately, a meta-analysis depends on the quality of the primary studies included in the analysis [2]. We believe that we performed a quality meta-analysis [3], confirmed by high scores on the Oxman and Guyatt index [5], a validated scoring system for the quality of meta-analyses and systematic reviews. Drs. Descatha, Huard, and Duval suggest that by combining studies that used different cross-sectional area cutoffs for positive diagnosis of carpal tunnel syndrome, our results may artificially influence the sensitivity and specificity of the sample. All meta-analyses carry this risk, and our study is no different. We agree that obtaining the raw data from all studies included in the analysis would have yielded more accurate results. However, as obtaining the raw data from every study is not possible, including only studies for which we were able to obtain raw data would introduce substantial selection bias. They also suggested that separate analyses should have been performed at each cross-sectional area cutoff value, however, this would decrease the sample size for each value and add more confusion to an already potentially confusing analysis. We thank Drs. Descatha, Huard, and Duval for observing our failure to include the likelihood ratios in the manuscript and have included a table detailing the ratios (Table 1). Table 1 Studies included in the meta-analysis [3] and reported likelihood positive and negative ratios We respectfully disagree that the specific transducer and ultrasound equipment used in each study is an important factor in the sensitivity and specificity of ultrasound as a diagnostic tool. We found no literature to support the advantage or disadvantage of one transducer over another. We did identify substantial heterogeneity in the criteria used for electrodiagnostic testing and clinical findings in the diagnosis of carpal tunnel syndrome. This heterogeneity, however, mirrors clinical reality where different institutions and physicians use varying criteria. We sincerely thank Descatha et al. for their thoughtful comments and hope we have addressed their concerns.