Dislocation and disappearance of muscle motor points in needle electromyography

Kovrazhkina E.A., Levitsky G.N., Kazakov D.O., Gaidash M.I.

1) Federal Center for Brain and Neurotechnology FMBA of Russia, Moscow, Russia; 2) “Gleb Levitsky Clinic” with a Private Center for Amyotrophic Lateral Sclerosis, Moscow, Russia; 3) Veltischev Research Clinical Institute of Pediatrics, Moscow, Russia; 4) Pirogov Russian National Research Medical University, Moscow, Russia; 5) Central Clinical Hospital with a Polyclinic of the Presidential Administration of the Russian Federation, Moscow, Russia

Background: Dislocation or disappearance of a motor point (MP) is the detection of MP in a location different from that indicated in the anatomical atlas or the inability to detect it with the maximum possible muscle tension.
Objective: Assessment of the prevalence and specificity of the phenomenon of MP dislocation/disappearance.
Materials and methods: Needle electromyography was performed on 120 muscles in patients with peripheral nervous system diseases with neurogenic denervation and with anxiety disorders without neurological symptoms. The depth of muscle paresis, spontaneous activity, parameters of motor unit potentials, and the nature of MP dislocation when detected were assessed. Magnetic resonance imaging (MRI) of the muscles was performed in 2 patients with MP dislocations. Additionally, 10 neurophysiologists were interviewed regarding the frequency of detection of the phenomenon.
Results: The phenomena of MP dislocation and disappearance were detected in 4.2% of the examined muscles; in 2 patients – with amyotrophic lateral sclerosis in the lateral gastrocnemius muscles, in 2 – with adult spinal muscular atrophy (SMA) in the common extensor of the fingers and the medial gastrocnemius muscle, respectively, in 1 – with anxiety disorder. MRI of the muscles in the patient with SMA showed a more pronounced signal change in the muscle with dislocation, in the patient with anxiety disorder – a normal MR signal in the affected muscle. Dislocated points in all cases were located proximally and lateral to the place of their «atlas» location. In sensorimotor axonal polyneuropathy and Parsonage-Turner syndrome, dislocation and disappearance of MP were not detected. Of the 10 surveyed neurophysiologists, 2 encountered the phenomenon of dislocation in the gastrocnemius muscles.
Conclusion: The phenomenon of MP dislocation/disappearance is rare in electromyographic practice. The phenomenon in neurological diseases is probably based on a change in the anatomical relationships of denervated muscles. Also, the disappearance of MP can be detected in patients with mental disorders when they interfere with the methodically correct conduct of the study.

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About the Authors

Elena A. Kovrazhkina, Cand. Sci. (Med.), Neurologist, Functional Diagnostics Specialist, doctor at the Functional Diagnostics Department, Federal Center for Brain and Neurotechnology of the Federal Medical and Biological Agency of Russia, Moscow, Russia
Gleb N. Levitsky, Cand. Sci. (Med.), Neurologist, Functional Diagnostics Specialist, General Director of the Gleb Levitsky Clinic with a Private Center for Amyotrophic Lateral Sclerosis, International Emissary for ALS Patients’ Rights, Moscow, Russia; alsrus@gmail.com (corresponding author)
Dmitry O. Kazakov, Radiologist, Research Clinical Institute of Pediatrics named after Acad. Yu.E. Veltischev; Pirogov Russian National Research Medical University, Moscow, Russia
Maksim I. Gaidash, Neurologist, Central Clinical Hospital with Outpatient Clinic of the Administrative Directorate of the President of the Russian Federation, Moscow, Russia

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