Does Needle EMG Interfere with MR Neurography or Myography Interpretation?

By Michael Rubin, MD

Professor of Clinical Neurology, Weill Cornell Medical College

SYNOPSIS: In this carefully designed prospective clinical study, needle electromyography did not have any significant effect on the interpretation of magnetic resonance (MR) neurography or MR myography or alter the diagnosis.

SOURCE: Sondermann S, Boppel T, Fieseler K, et al. Needle electromyography does not meaningfully impact findings in MR-neurography/-myography. Muscle Nerve 2024;69:409-415.

Magnetic resonance neurography (MRN) connotes high-resolution MR imaging (MRI) of peripheral nerves, using a combination of MR techniques to evaluate nerve pathology. MR myography (MRM), MRI of muscle, extends the information provided by MRN regarding nerve morphology to evaluate neuropathic changes in muscle. An increase in the short tau inversion recovery (STIR) signal correlates with nerve lesion severity on electromyography (EMG), which results in denervation edema assumed to be the consequence of water diffusion from intracellular to extracellular spaces. Might needle EMG, which can result in hematoma formation in up to 29% of cases, interfere with MRN/MRM interpretation by causing focal bleeding or edema along the needle track?

Between February 2019 and December 2020, inpatients undergoing routine needle EMG of the tibialis anterior muscle at the University Medical Center Schleswig-Holstein, Lübeck, Germany, were enrolled in this prospective longitudinal study where MRN/MRM was performed before and two to six hours after EMG, with a follow-up MRN/MRM performed on day 2 or 3 if the patient remained hospitalized. Inclusion criteria required ages between 20 and 80 years and a clinically warranted EMG, with the single exclusionary criterion being contraindications for MRI.

Patients received MRN/MRM scans in the supine position using a 3T scanner, with the coil centered distal to the knee, one-third of the way between the knee and ankle, using MR-SPOT packets to mark each of the four to five concentric needle insertions. Needle insertions varied in depth and position, with data collected for the presence of spontaneous activity and quantitative motor unit analysis. Images were interpreted independently by three neuroradiologists, with a consensus obtained for divergent readings, and statistical analysis comprised the paired t-tests with P < 0.05 considered significant.

Among seven men and three women (median age 71.6 years) who underwent pre- and post-EMG MRI, four of whom also had follow-up MRI, oral anticoagulants or aspirin were taken by three and two patients, respectively. Subcutaneous low-molecular-weight heparin was administered for deep vein thrombosis prophylaxis to all patients not receiving oral anticoagulants. Two patients had spontaneous activity and six patients had changes in motor unit potential parameters. Focal edema was found in nine patients at the labeled positions on the post-EMG MRI, with up to three lesions observed per muscle, and micro-hematomas were seen in five of the 10. All lesions were small and circumscribed, with none causing any generalized change in muscle signal intensity.

Of four patients who underwent day 2-3 follow-up MRI, three patients who had edematous lesions on the post-EMG MRI now had diminished edema. All neuroradiologists agreed that the needle lesions did not impair interpretation of any general denervation edema that was present. MRN/MRM detects focal edema or hematomas caused by recent needle EMG, but their presence does not impair MRI interpretation.

COMMENTARY

Comprising 40% of body mass and containing 50% to 75% of all body proteins, skeletal muscle is the largest organ system in the body. The ability to comprehensively assess skeletal muscle health in vivo and establish biomarkers would be very helpful in evaluating muscle disease, muscle injury, and muscle pain. To date, these modalities include EMG, ultrasound, MRI, computed tomography, dual-energy X-ray absorptiometry, and isokinetic dynamometry. Ultrasound has the advantage, in that it may be used in a dynamic manner, allowing study of muscle during contraction and exercise. Tensiomyography assesses muscle contractile properties, including
muscle displacement, contraction time, and muscle relaxation time, which reflect muscle stiffness, contractile speed, and muscle fiber recruitment patterns. Since this provides objective and quantitative data that can be tracked over sequential studies, tensiomyography has become popular in sports science, rehabilitation, and research settings, offering real-time, reliable data on muscle function.¹ Continued technical advances in assessing skeletal muscle health will provide insights into these topics in health and disease.

REFERENCE

1. Beausejour JP, Knowles KS, Wilson AT, et al. Innovations in the assessment of skeletal muscle health: A glimpse into the future. Int J Sports Med 2024; Feb 24. doi: 10.1055/a-2242-3226. [Online ahead of print].