Unexpected Intermediate Nerve Conduction Velocity Findings in Charcot-Marie-Tooth Syndromes Classified as Demyelinated or Axonal in a Pediatric Population

Abstract

Introduction Among the hereditary motor and sensory neuropathies (HMSN), demyelinating forms are the best characterized, with a clear predominance of CMT1A. The axonal and intermediate forms are less described. The aim of this study is to report the genetic diagnosis of Charcot-Marie-Tooth (CMT) according to the nerve conduction velocity (NCV) findings in a pediatric population.

Methods We retrospectively described a population of HMSN children with a confirmed genetic diagnosis of demyelinated, intermediate, or axonal forms. We compared the results of the genetic analyses with those of motor NCV in median nerve according to whether they were below 25 m/s (demyelinating group); between 25 and 45 m/s (intermediate group), or above 45 m/s (axonal group).

Results Among the 143 children with an HMSN, 107 had a genetic diagnosis of which 61 had an electromyogram. On NCV findings: seven (11%) pertain to the axonal group, 20 (32%) to the intermediate group, and 34 (55%) to the demyelinating group. When NCV was above 45 m/s, CMT2A was the predominant genetic diagnosis (70%) when NCV were below 25 m/s, CMT1A was the predominant genetic diagnosis (71%). Intermediate NCV findings group was the more heterogeneous with seven genetic CMT subgroups (60% CMT1A, CMT1B, CMT1X, CMT2A, CMT2N, CMT4G).

Conclusion Taking NCV values between 25 and 45 m/s to define an intermediate group of CMT in children leads to the inclusion of non-typically “intermediate”, especially CMT1A. We emphasize the broad spectrum of NCV in CMT1A that justified the systematic search of PMP22 duplication/deletion screening before next generation sequencing panel.

Keywords

Charcot-Marie Tooth - hereditary motor and sensory neuropathies - intermediate CMT - axonal CMT - children

Ethical Publication Statement

We declare that we have read the journal's position relating to ethical publication issues and confirm that this report is consistent with those guidelines.

Author's Contribution

E.B. wrote the first draft of the manuscript, tables, and figure. C.C., U.W.L., and F.R. followed patients included in this study. They all made critical amendments and essential feedback to this manuscript. C.M. and P.L. performed genetic analysis. R.J.-m. and P.C. performed and discussed electroneuromyographic analysis. P.C. made essential feedback to the manuscript. All authors have approved the final article.

Publication History

Received: 17 September 2021

Accepted: 13 January 2022

Article published online:
16 March 2022

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