Difference between revisions of "5° Clinical case: Spontaneous Electromyographic Activity"

Zieliński et al.<ref>Grzegorz Zieliński, Aleksandra Byś, Jacek Szkutnik, Piotr Majcher, Michał Ginszt. Electromyographic Patterns of Masticatory Muscles in Relation to Active Myofascial Trigger Points of the Upper Trapezius and Temporomandibular Disorders. Diagnostics (Basel) 2021 Apr; 11(4): 580.  Published online 2021 Mar 24. doi: 10.3390/diagnostics11040580 PMCID: PMC8063936</ref> noted that changes in electromyographic patterns of masticatory muscles may be associated with the presence of pain due to active myofascial trigger points (MTrPs)<ref>Fernández-de-Las-Peñas C., Galán-Del-Río F., Alonso-Blanco C., Jiménez-García R., Arendt-Nielsen L., Svensson P. Referred Pain from Muscle Trigger Points in the Masticatory and Neck-Shoulder Musculature in Women with Temporomandibular Disoders. J. Pain. 2010;11:1295–1304. doi: 10.1016/j. jpain.2010.03.005.</ref><ref>Peck C., Murray G., Gerzina T. How Does Pain Affect Jaw Muscle Activity? The Integrated Pain Adaptation Model. Aust. Dent. J. 2008;53:201–207. doi: 10.1111/j.1834-7819.2008.00050.x.</ref><ref>Pietropaoli D., Ortu E., Giannoni M., Cattaneo R., Mummolo A., Monaco A. Alterations in Surface Electromyography Are Associated with Subjective Masticatory Muscle Pain. Pain Res. Manag. 2019;2019:6256179. doi: 10.1155/2019/6256179. </ref><ref>Manfredini D., Cocilovo F., Favero L., Ferronato G., Tonello S., Guarda-Nardini L. Surface Electromyography of Jaw Muscles and Kinesiographic Recordings: Diagnostic Accuracy for Myofascial Pain. J. Oral Rehabil. 2011;38:791–799. doi: 10.1111/j.1365-2842.2011.02218.x. </ref><ref>Simons D.G., Travell J.G., Simons L.S. Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. 2nd ed. Williams & Wilkins; Baltimore, MD, USA: 1999.</ref> and furthermore, during electromyography examination, significantly higher values of activity at rest within the anterior temporalis muscle were observed among MTrPs and TMDs patients compared to healthy individuals. The authors conclude that this altered pattern may be related to the presence of active MTrPs in the trapezius muscle, which, as a result of a referred pain mechanism, alters the activity of the anterior temporal (TA)   

Furthermore, the same author<ref>Grzegorz Zieliński, Aleksandra Byś, Michał Ginszt, Michał Baszczowski, Jacek Szkutnik, Piotr Majcher, Piotr Gawda. Depression and Resting Masticatory Muscle Activity. J Clin Med. 2020 Apr; 9(4): 1097.  Published online 2020 Apr 12. doi: 10.3390/jcm9041097</ref> has reviewed numerous clinical studies demonstrating that depression has a substantial effect on the stomatognathic system, including the activity of the masticatory muscles, which can lead to temporomandibular disorders. Furthermore, an increase in the bioelectrical activity of the masseter muscles was observed in subjects with depressive symptoms.<ref>Stocka A., Sierpinska T., Kuc J., Golebiewska M. Relationship between depression and masticatory muscles function in a group of adolescents. Cranio. 2018;36:390–395. doi: 10.1080/08869634.2017.1364030.</ref> Therefore, the aim of the study by Zieliński et al. was to determine the influence of depression quantified through the axis II protocol of RDC/TMD on the resting bioelectrical activity of the masseter and temporalis muscles. The conclusion was that moderate depression determined on the basis of the RDC/TMDs II axis questionnaire is not related to the resting activity of the selected masticatory muscles and that further research should be continued on a larger group of respondents in order to establish the relationship between psychological factors and bioelectrical parameters of masticatory muscles.  

In one subject, the insertion activity appears as high-frequency positive and negative spikes in a single group and are typically a representation of muscle fiber damage or mechanical stimulation due to needle penetration into the muscle. In our patient this activity occurred with a duration of 80 mS and was referable to a normal picture. Also note the phenomenon of plaque activity. If a needle electrode is held stationary at one point in the muscle, normal muscles at rest show absolutely no electrical activity except in the region of the neuromuscular endplate. These consist of two components: low amplitude (on the order of 10-50 μV) and low duration (1-2 msec) which to the loudspeaker EMG resemble the sound of sea shells on the ear. In our case (fig.1A) the total absence of plaque activity in the right masseter can be explained by the recording performed with surface electrodes which partially reduce the energy of the signal but the activity recorded on the left masseter, again with surface, has a width of<math>\approxeq100\mu V</math> . For the same reasoning, this activity should not be considered as plate activity since, as can be seen in fig. 1B, recording of the left masseter performed with a coaxial electrode, the amplitude is <math>\approxeq 400\mu V</math>. Sometimes plaque potential spikes are indistinguishable in waveform from fibrillation potentials which also show initial negativity when recorded near the plaque. Another curious element is the similarity of the discharge model between the discharges of the neuromuscular spindles and of the plate potentials, so much so that some authors<ref>Partanen JV, Nousiainen U. : End-plate spikes in the electromyography are fusimotor unit potentials. Neurology 1983; 33:039-1043, </ref> hypothesized that these potentials could originate from the intrafusal muscle fibers. The discussion and the electrophysiological meaning to be given to the electrical activity observable in fig. 1B.

In the first 2 weeks after denervation, the sensitivity of a muscle fiber to acetylcholine (ACh) increases up to 100-fold. This phenomenon known as “denervation hypersensitivity” may explain the spontaneous firing of denervated muscle fibers in response to minute ACh quanta.<ref>Axelsson J, Thesleff S.: A study of super-sensitivity of denervated mammalian skeletal muscles. J Physiol (Lond) 1957:149;178-193</ref> The fact that the infusion of curare blocks the receptors of the neuromuscular plate but does not abolish the spontaneous discharge, that the denervation of the frog muscle can lead to an increased sensitivity to ACh but not generate spontaneous activity. <ref>Miledi R.: The acetylcholine sensitivity of frog musclefibres after complete or partial denervation. J Physiol (Lond) 1960:151;1-23 </ref>. These studies have suggested an alternative hypothesis that of slow changes in membrane potentials of metabolic origin which can periodically reach a critical level and evoke propagated spikes.<ref>Thesleff S: Fibrillation in denervated mammalian skeletal muscle. In Cukp WL e Ochoa J (eds): Abnormal Nerves and Muscle as Impulse Genertors. Oxford University Press. Oxford 1982, pp 678-694</ref>