Needle electromyography in carpal tunnel syndrome: is it valuable or predictable?

Wafaa S El-Emary,Marwa M Hassan

doi:10.4103/1110-161x.177426

Wafaa S El-Emary, Marwa M Hassan

Open Access

https://doi.org/10.4103/1110-161x.177426

Copy DOI

Abstract

Needle electromyography (EMG) examination is not crucial in establishing the diagnosis of carpal tunnel syndrome (CTS). However, the presence of axonal loss in needle EMG helps clinicians determine a treatment strategy such as surgery. The aim of this study was to investigate whether needle EMG in CTS patients is essentially needed or could be predicted using other nerve conduction study (NCS) parameters. This study included 100 patients with clinical and NCS-proven CTS, as well as 50 age-matched and sex-matched controls. All individuals were evaluated using electrodiagnostic techniques, including median distal latency, compound muscle action potential (CMAP), forearm motor nerve conduction velocity, median peak latency, sensory nerve action potentials, and sensory nerve conduction velocity. All CTS patients underwent EMG examination of the abductor pollicis brevis muscle, and the presence or absence of spontaneous EMG activity was recorded. Comparison of the NCS parameters between CTS patients with and without spontaneous EMG activity revealed that the main determinant parameters for spontaneous activity were CMAPs, sensory nerve action potentials, and forearm motor nerve conduction velocities. However, logistic regression analysis showed that CMAP was the most powerful predictor of the presence of spontaneous activity (P = 0.000, odds ratio = 12.154). It can be concluded that median nerve CMAP amplitudes are the most powerful predictors of the occurrence of spontaneous EMG activity. However, EMG examination is still valuable in some CTS patients and NCS cannot completely replace needle EMG examination in these patients.

Highlights

Carpal tunnel syndrome (CTS) is the most commonly studied focal neuropathy [1,2]
Needle EMG can detect the presence of membrane instability by recording denervation potentials, such as fibrillation potentials and positive sharp waves, and altered motor unit morphology
With severe CTS, electrodiagnostic evidence of axonal loss of motor nerves and subsequent motor unit reorganization can be seen in the abductor pollicis brevis (APB) muscle [1]

Summary

Introduction

Carpal tunnel syndrome (CTS) is the most commonly studied focal neuropathy [1,2]. It accounts for 90% of all entrapment neuropathies [3,4]. Nerve conduction studies (NCS) are more valuable compared with needle electromyography (EMG) in the diagnosis of CTS, because the underlying pathophysiology is mainly focal demyelination [1]. In CTS, both axonal degeneration and conduction block (CB) can cause weakness, in addition to electrophysiological findings such as impaired voluntary recruitment of motor units as well as low amplitude (even absent) compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) [5,6]. The decision whether or not to perform needle EMG in patients with CTS is not agreed upon universally [9,11,12]

Objectives

Methods

Results

Conclusion