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Comparison of the electrophysiological characteristics of tight filum terminale and tethered cord syndrome

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Abstract

Purpose

This study aims to characterize tight filum terminale (TFT) in motor evoked potential (MEP) testing by comparing TFT patients with both tethered cord syndrome (TCS) patients and healthy subjects.

Methods

Fifty TFT patients, 18 TCS patients, and 35 healthy volunteers participated in this study. We recorded MEPs following transcranial magnetic stimulation from the bilateral abductor hallucis muscles as well as compound muscle action potentials and F-waves evoked by electrical stimulation of the tibial nerve from the bilateral abductor pollicis brevis muscles. The peripheral conduction time (PCT) was calculated from the latency of the compound action potential and F-wave. Furthermore, the central motor conduction time (CMCT) was calculated by subtracting PCT from MEP latency.

Results

TFT and TCS patients had a significantly longer MEP latency than healthy subjects. PCT in TFT patients was significantly longer than those in TCS patients or healthy subjects. Using the cutoff values for PCT, we were able to diagnose patients with TFT patients with a sensitivity of 72.0% and a specificity of 91.4%.

Conclusion

Prolonged PCT in the MEP test may be a useful indicator for TFT and suggests that MEP may be used as an adjunct diagnostic tool for TFT.

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Acknowledgements

We would like to thank Editage (www.editage.com) for English language editing.

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan

    Naosuke Kamei, Toshio Nakamae, Taiki Morisako, Takahiro Harada, Toshiaki Maruyama & Nobuo Adachi

  2. Department of Orthopaedic Surgery, Nihon University, Tokyo, Japan

    Kazuyoshi Nakanishi

Authors
  1. Naosuke Kamei
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  2. Toshio Nakamae
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  3. Kazuyoshi Nakanishi
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  4. Taiki Morisako
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  6. Toshiaki Maruyama
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  7. Nobuo Adachi
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Correspondence to Naosuke Kamei.

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Conflict of interest

The authors declare no conflicts of interest. No funds were received in support of this work.

Ethical approval

This study was conducted in accordance with the ethical standards of our institutional and national research committees and the 1964 Declaration of Helsinki and its subsequent amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.

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Comments

Kamei et al. have investigated the value of clinical neurophysiological testing in patients with tethered cord syndrome (TCS) and tight filum terminale (TFT). Their main finding is that peripheral conduction time (PCT) was prolonged only in TFT but not in TCS patients and, therefore, may represent a neurophysiological adjunctive diagnostic aid to diagnose a TFT. This is an interesting study that could potentially contribute to clarify neurophysiological charachteristics of various dysraphisms. Yet, one of the main limitations of this study is that all TCS patients had a conus tip at the level of the sacrum, and therefore they are not representative of TCS population, where the conus can be tethered at any level between L2/L3 and the sacrum. As such, the PCT in another group of TCS patients may be longer and not significantly different from that in the TFT group. It also remains disputable why PCT should be selectively prolonged only in TFT and not in TCS patients. Further studies are needed to confirm the intriguing results of Kamei et al.

Francesco Sala

Verona, Italy

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Kamei, N., Nakamae, T., Nakanishi, K. et al. Comparison of the electrophysiological characteristics of tight filum terminale and tethered cord syndrome. Acta Neurochir 164, 2235–2242 (2022). https://doi.org/10.1007/s00701-022-05298-4

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  • DOI: https://doi.org/10.1007/s00701-022-05298-4

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