Improving Indirect Methods for Calculating Reference Limits for Nerve Conduction Studies From Historical Data

Muscle & Nerve, vol. 74, pp. 328–338

Abstract

INTRODUCTION/AIMS: High quality reference limits for nerve conduction studies (NCS) are essential for diagnosis of neuromuscular disorders. Examining healthy controls to calculate reference limits directly is expensive and time consuming. Indirect methods, including extrapolated norms (E-norms), extrapolated reference values (E-Ref), and multivariate extrapolated reference values (MeRef), use historical hospital data instead. These methods sort the historical measurements in increasing order, creating so-called S-curves, and select normal measurements based on the shape of these S-curves. Current versions of these methods have several limitations, and we aimed to improve them by modifying how they select normal measurements. METHODS: E-norms, E-Ref, and MeRef were modified with new S-curve selection algorithms. The modified versions of the methods were used to calculate reference limits for common NCS measurements from a large historical database. The results were compared to reference limits calculated from 680 healthy subjects using Youden's J statistic and z-score deviation. RESULTS: The modified methods provided reference limits with Youden's J > 0.8 and z-score deviation < 0.9 for most types of NCS measurements and similar or higher Youden's J than the unmodified methods. In most cases, the methods required at least 500 measurements and fewer than 20% abnormal measurements for good performance. DISCUSSION: Changing the S-curve selection algorithms improves E-norms, E-Ref, and MeRef. The modifications require a sufficient number and proportion of normal measurements in the historical database. When these prerequisites are met, a combination of indirect methods can be used when developing reference limits from historical patient data.

Authors 11

1. Tomasz Szymon Szczepanski corresponding

   Oslo University Hospital · University of Oslo

   Affiliation as printed

   Faculty of Medicine University of Oslo Oslo Norway

   Section for Clinical Neurophysiology, Department of Neurology Oslo University Hospital Oslo Norway

2. Kristian Bernhard Nilsen

   Oslo University Hospital

   Affiliation as printed

   Section for Clinical Neurophysiology, Department of Neurology Oslo University Hospital Oslo Norway

3. Øystein Dunker

   Oslo University Hospital · University of Oslo

   Affiliation as printed

   Department of Research and Innovation, Division of Clinical Neuroscience Oslo University Hospital Oslo Norway

   Faculty of Medicine University of Oslo Oslo Norway

   Section for Clinical Neurophysiology, Department of Neurology Oslo University Hospital Oslo Norway

4. Andrew H. Reiner

   Oslo University Hospital

   Affiliation as printed

   Oslo Centre for Biostatistics and Epidemiology Oslo University Hospital Oslo Norway

5. Trond Sand

   Norwegian University of Science and Technology · St Olav's University Hospital

   Affiliation as printed

   Department of Neurology and Clinical Neurophysiology St. Olavs Hospital Trondheim Norway

   Department of Neuromedicine and Movement Science, Faculty of Medicine and Health Sciences Norwegian University of Science and Technology Trondheim Norway

6. Martijn Tannemaat Aachen

   Leiden University Medical Center

   Affiliation as printed

   Leiden University Medical Center Leiden the Netherlands

7. Anis Yazidi

   OsloMet – Oslo Metropolitan University

   Affiliation as printed

   Oslo Metropolitan University Oslo Norway

8. Kerstin Bach

   Norwegian University of Science and Technology

   Affiliation as printed

   Department of Computer Science Norwegian University of Science and Technology Trondheim Norway

9. John Anker Zwart

   Oslo University Hospital · University of Oslo

   Affiliation as printed

   Department of Research and Innovation, Division of Clinical Neuroscience Oslo University Hospital Oslo Norway

   Faculty of Medicine University of Oslo Oslo Norway

10. Joe F. Jabre

    Tufts University

    Affiliation as printed

    Department of Public Health and Community Medicine Tufts University School of Medicine Boston Massachusetts USA

11. Petter Moe Omland

    Norwegian University of Science and Technology · St Olav's University Hospital

    Affiliation as printed

    Department of Neurology and Clinical Neurophysiology St. Olavs Hospital Trondheim Norway

    Department of Neuromedicine and Movement Science, Faculty of Medicine and Health Sciences Norwegian University of Science and Technology Trondheim Norway

    Department of Radiology and Nuclear Medicine St. Olavs Hospital, Trondheim University Hospital Trondheim Norway

    NorHEAD—Norwegian Centre for Headache Research NTNU Trondheim Norway