Intraepineurial fat quantification and cross-sectional area analysis of the sciatic nerve using MRI in Charcot-Marie-Tooth disease type 1A patients

Hyun Su Kim,Soo Hyun Nam,Hojeong Won,Min Jae Cha,Byung-Ok Choi,Seonwoo Kim,Young Cheol Yoon,Ji Hyun Lee,Hye Mi Kwon

doi:10.1038/s41598-021-00819-0

Abstract

The objectives of this study were to assess the fat fraction (FF) and cross-sectional area (CSA) of the sciatic nerve in Charcot-Marie-Tooth disease type 1A (CMT1A) patients using Dixon-based proton density fat quantification MRI and to elucidate its potential association with clinical parameters. Thigh MRIs of 18 CMT1A patients and 18 age- and sex-matched volunteers enrolled for a previous study were reviewed. Analyses for FF and CSA of the sciatic nerve were performed at three levels (proximal to distal). CSA and FF were compared between the two groups and among the different levels within each group. The relationship between the MRI parameters and clinical data were assessed in the CMT1A patients. The CMT1A patients showed significantly higher FF at level 3 (p = 0.0217) and significantly larger CSA at all three levels compared with the control participants (p < 0.0001). Comparisons among levels showed significantly higher FF for levels 2 and 3 than for level 1 and significantly larger CSA for level 2 compared with level 1 in CMT1A patients. CSA at level 3 correlated positively with the CMT neuropathy score version 2 (CMTNSv2). In conclusion, the sciatic nerve FF of CMT1A patients was significantly higher on level 3 compared with both the controls and the measurements taken on more proximal levels, suggesting the possibility of increased intraepineurial fat within the sciatic nerves of CMT1A patients, with a possible distal tendency. Sciatic nerve CSA at level 3 correlated significantly and positively with CMTNSv2, suggesting its potential value as an imaging marker for clinical severity.

Highlights

Abbreviations CMT Charcot-Marie-Tooth disease PMP Peripheral myelin protein cross-sectional area (CSA) Cross-sectional area magnetic resonance imaging (MRI) Magnetic resonance imaging fat fraction (FF) Fat fraction region of interest (ROI) Region of interest CMTNSv2 CMT neuropathy score version 2 compound muscle action potentials (CMAPs) Compound muscle action potential nerve conduction velocities (NCVs) Nerve conduction velocity sensory nerve action potentials (SNAPs) Sensory nerve action potential IQR Interquartile range
We found significantly higher FF values for the sciatic nerve at level 3, the most distal of the measured levels, in the patient group compared with the control group
Comparisons among FFs measured at different levels within the CMT type 1A (CMT1A) patient group showed that levels 2 and 3 had significantly higher values than level 1

Summary

Introduction

Abbreviations CMT Charcot-Marie-Tooth disease PMP Peripheral myelin protein CSA Cross-sectional area MRI Magnetic resonance imaging FF Fat fraction ROI Region of interest CMTNSv2 CMT neuropathy score version 2 CMAP Compound muscle action potential NCV Nerve conduction velocity SNAP Sensory nerve action potential IQR Interquartile range. Studies using a rat model of CMT1A have reported that Schwann cells in this disease exhibit reduced transcription of the genes required for myelin lipid biosynthesis[11,12,13,14]. A few studies using magnetic resonance imaging (MRI) have suggested that an increase in interfascicular fat content within peripheral nerves could occur in CMT p atients[16,17]. The study of Ratner et al opened the possibility of applying this imaging technique to peripheral nerve structures[25] They found Dixon-based MRI to be a reliable tool for measuring FF, mostly representing interfascicular fat, in the sciatic nerves of normal subjects. Measuring intraepineurial FF using Dixon-based MRI in neuromuscular disorders such as CMT has not been reported to our knowledge

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