Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies

Summary

Here we present a protocol using nerve conduction studies and ultrasound to screen potential axonal degeneration associated with carpal tunnel syndrome. The criteria for differentiation are established. Compared to conventional approaches, this method is noninvasive, convenient, and efficient, with an overall satisfactory accuracy, sensitivity, and specificity.

Abstract

Axonal degeneration, indicative of surgical decompression, may coexist in carpal tunnel syndrome (CTS) as the disease progresses. However, the current diagnostic and severity gradation system cannot clearly indicate its coexistence, resulting in confusion of appropriate treatment prescription. There are also constraints in conventional methods for differentiation as well. This study aims at introducing an innovative, efficient, and quick screening protocol to differentiate axonal degeneration associated with CTS, using ultrasound and nerve conduction studies (NCS). It starts by using NCS to perform orthodromic stimulation at the wrist, to obtain the sensory conduction of the median and the ulnar nerves respectively. Meanwhile, the motor conduction of the median nerve is collected by stimulating the palm, wrist, and elbow, followed by the stimulation of the ulnar nerve at the wrist, below and above the elbow. Then, an ultrasound assessment is performed, using a linear array transducer, with cross-sectional area (CSA) and perimeter (P) at the wrist and at the one-third distal forearm calipered. Ratios (R-CSA, R-P) and changes from wrist to one-third distal forearm (ΔCSA and ΔP) are calculated according to a standard format. Potential axonal degeneration coexisting in CTS will be screened according to the criteria of NCS and cut-off values of ultrasound measurements established in a previous study. In terms of its noninvasiveness, low cost, convenience, and efficiency, it is easy to apply ultrasound complimentarily in clinical practice to prescreen patients with potential coexisting axonal degeneration. Nevertheless, the ultrasonographic imaging cannot directly reflect axonal degeneration. It still relies on conventional but invasive methods such as electromyography (EMG) and biopsy for confirmation if needed.

Introduction

CTS is pathologically a disorder with segmental demyelination, whereas secondary axonal degeneration, which is indicative of surgical decompression, may coexist as the disease progresses¹. However, the current diagnostic and severity gradation scale (from mild to very severe grade) for CTS cannot clearly indicate any coexistence of axonal degeneration, resulting in confusion when choosing the appropriate treatment. Conventional methods for confirming axonal degeneration, such as needle EMG and nerve biopsy, can be sensitive and accurate, but they are both restricted in the clinical practice due to their invasiveness²

Protocol

All the procedures have been approved by the University of Hong Kong/Hospital authorities Hong Kong West Institutional Review Board (HKU/HA HKW IRB, Ref. Number: UW17-129).

This protocol is applicable to patients who demonstrated clinical symptoms such as numbness, tingling, or pain over the median nerve-innervated area of the hand, with a positive outcome in Tinel's sign and Phalen's test. Those subjects with comorbidities, such as diabetes mellitus, cancer, rheumatoid arthritis, and .......

Discussion

It is challenging to set up a universal standard for the measurement of NCS due to the influence of demographic and physical factors such as age, gender, ethnicities, and body weight, etc.¹⁴. Regarding SNAP amplitude, there is a difference between the orthodromic (the direction of currency runs proximally toward the body) and antidromic (the direction of currency runs distally away from the body) technique, as the SNAP amplitude measured by the orthodromic method is smaller than the .......

Materials

Name	Company	Catalog Number	Comments
Nicolet Viking EDX	Nicolet	RY111820G
MyLab Twice	ESAOTE	101620000