A new method to define cutoff values in nerve conduction studies for carpal tunnel syndrome considering the presence of
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ORIGINAL ARTICLE
A new method to define cutoff values in nerve conduction studies for carpal tunnel syndrome considering the presence of false-positive cases Yosuke Miyaji 1,2 & Masahito Kobayashi 3 & Chizuko Oishi 1,4 & Yoshikazu Mizoi 1,5 & Fumiaki Tanaka 2 & Masahiro Sonoo 1 Received: 7 November 2018 / Accepted: 7 November 2019 # Fondazione Società Italiana di Neurologia 2019
Abstract Background Nerve conduction studies (NCS) are useful tools for diagnosing carpal tunnel syndrome (CTS). Establishing the normal values is the first step required for utilizing NCS for diagnosis. Previous epidemiological studies demonstrated the presence of fairly large number of false-positive subjects regarding NCS among control population, which has not been properly considered in past studies. This study proposed a new method to address this issue. Methods Non-diabetic 144 CTS patients were retrospectively enrolled using clinically defined inclusion criteria. Controls consisted of 73 age-matched volunteers without hand symptoms. Six NCS parameters were evaluated including peak-latency difference by the thumb method (thumbdif) and that by the ring-finger method (ringdif). The Youden index of the receiver operator characteristic curve was used both to judge the sensitivity of a parameter and to identify false-positive cases that were thought to have subclinical median neuropathy at the wrist. The linear function of six parameters was constructed, and the coefficient for each parameter was variously changed. Results When the Youden index took on the maximum value, seven control subjects (10%) were identified as false-positive and were excluded from the calculation of normal values. The most sensitive parameter before exclusion was thumbdif, whereas ringdif became the most sensitive after exclusion. The cut-off value for ringdif was 1.15 ms before exclusion, but was 0.37 ms after exclusion. Conclusion This method can be widely applied to solve the statistical Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation problem when the gold standard is lacking, and the outside reference standard is not completely reliable. Keywords Carpal tunnel syndrome . False-positive cases . Nerve conduction study . Receiver operator characteristic curve . Youden index
Introduction * Masahiro Sonoo [email protected] 1
Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan
2
Department of Neurology and Stroke Medicine, Yokohama City University Graduate School of Medicine, Yokohama, Japan
3
Faculty of Economics, Yokohama National University, Yokohama, Japan
4
Department of Neurology, Faculty of Medicine, Kyorin University, Tokyo, Japan
5
Department of Neurology, Saitama Medical University, Saitama, Japan
Nerve conduction studies (NCS) are useful tools for diagnosing carpal tunnel syndrome (CTS). Defining cut-off values for individual NCS parameters is a prerequisite to utilize NCS in clinical practice, although this procedure may have following inherent problem. Several authors have
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