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Kouyoumdjian JA, Estephan EDP. Electrophysiological evaluation of the neuromuscular junction: a brief review. ARQUIVOS DE NEURO-PSIQUIATRIA 2023; 81:1040-1052. [PMID: 38157872 PMCID: PMC10756823 DOI: 10.1055/s-0043-1777749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 11/17/2023] [Indexed: 01/03/2024]
Abstract
The nerve terminal and muscle membrane compose the neuromuscular junction. After opening the voltage-gated calcium channels, action potentials from the motor axons provoke a cascade for the acetylcholine release from synaptic vesicles to the synaptic cleft, where it binds to its receptor at the muscle membrane for depolarization. Low amplitude compound muscle action potential typically presents in presynaptic disorders, increasing by more than 100% after a 10-second effort in the Lambert-Eaton myasthenic syndrome and less in botulism. Needle electromyography may show myopathic motor unit action potentials and morphological instability ("jiggle") due to impulse blocking. Low-frequency repetitive nerve stimulation (RNS) is helpful in postsynaptic disorders, such as myasthenia gravis and most congenital myasthenic syndromes, where the number of functioning acetylcholine receptors is reduced. Low-frequency RNS with a decrement >10% is abnormal when comparing the 4th to the first compound muscle action potential amplitude. High-frequency RNS is helpful in presynaptic disorders like Lambert-Eaton myasthenic syndrome, botulism, and some rare congenital myasthenic syndromes. The high-frequency RNS releases more calcium, increasing the acetylcholine with a compound muscle action potential increment. Concentric needle records apparent single-fiber action potentials (spikes). A voluntary activation measures the jitter between spikes from two endplates. An electrical activation measures the jitter of one spike (one endplate). The jitter is the most sensitive test for detecting a neuromuscular junction dysfunction. Most neuromuscular junction disorders are responsive to treatment.
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Affiliation(s)
- João Aris Kouyoumdjian
- Faculdade de Medicina de São José do Rio Preto, Departamento de Ciências Neurológicas, Psiquiatria e Psicologia Médica, São José do Rio Preto SP, Brazil.
| | - Eduardo de Paula Estephan
- Faculdade de Medicina de São José do Rio Preto, Departamento de Ciências Neurológicas, Psiquiatria e Psicologia Médica, São José do Rio Preto SP, Brazil.
- Universidade de São Paulo, Departamento de Neurologia, São Paulo SP, Brazil.
- Faculdade de Medicina Santa Marcelina, São Paulo SP, Brazil.
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Kouyoumdjian JA, Graca CR. Concentric needle jitter: Reference values in stimulated Tibialis Anterior muscle. Front Neurol 2022; 13:957174. [PMID: 35937059 PMCID: PMC9355656 DOI: 10.3389/fneur.2022.957174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Accepted: 06/23/2022] [Indexed: 12/04/2022] Open
Abstract
Calculating the reference values for jitter parameters utilizing a disposable concentric needle have been already done for the most often tested muscles. Jitter, expressed as the mean consecutive difference (MCD), was measured in the Tibialis Anterior (TA), not routinely tested muscle. Jitter measurement was taken using the intramuscular microaxonal stimulation technique in 32 healthy subjects. The mean MCD and the mean MCD of the 27th value from the 32 subjects had a normal distribution and were 19.79 ± 2.72 μs and 26.88 ± 3.56 μs, respectively. The suggested limit for the mean MCD is ≥ 26 μs and for the individual values is > 34 μs.
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Affiliation(s)
- João Aris Kouyoumdjian
- Neuromuscular Investigation Laboratory, Department of Neurological Sciences, Psychiatry and Medical Psychology, State Medical School (FAMERP), São Paulo, Brazil
| | - Carla Renata Graca
- Neuromuscular Investigation Laboratory, Department of Neurological Sciences, Psychiatry and Medical Psychology, State Medical School (FAMERP), São Paulo, Brazil
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Sanders DB, Kouyoumdjian JA, Stålberg EV. Single fiber electromyography and measuring jitter with concentric needle electrodes. Muscle Nerve 2022; 66:118-130. [PMID: 35694863 DOI: 10.1002/mus.27573] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 05/06/2022] [Indexed: 11/07/2022]
Abstract
This monograph contains descriptions of the single fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNEs). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional electromyography should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.
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Affiliation(s)
- Donald B Sanders
- Department of Neurology, Duke University Medical Center, Durham, North Carolina, USA
| | - João A Kouyoumdjian
- Department of Neurological Sciences, State Medical School (FAMERP), São Paulo, Brazil
| | - Erik V Stålberg
- Department of Clinical Neurophysiology, Academic Hospital, Uppsala, Sweden
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Sanders DB, Kouyoumdjian JA, Stålberg EV. Single fiber EMG and measuring jitter with concentric needle electrodes. Muscle Nerve 2022. [PMID: 35652573 DOI: 10.1002/mus.27572] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 05/05/2022] [Indexed: 11/08/2022]
Abstract
This monograph contains descriptions of the single-fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNE). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional EMG should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.
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Affiliation(s)
- Donald B Sanders
- Department of Neurology, Duke University Medical Center, Durham, North Carolina, USA
| | - João A Kouyoumdjian
- Department of Neurological Sciences, State Medical School (FAMERP), São Paulo, Brazil
| | - Erik V Stålberg
- Department of Clinical Neurophysiology, Academic Hospital, Uppsala, Sweden
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Kouyoumdjian JA, Paiva GP, Stålberg E. Concentric Needle Jitter in 97 Myasthenia Gravis Patients. Front Neurol 2020; 11:600680. [PMID: 33281737 PMCID: PMC7691317 DOI: 10.3389/fneur.2020.600680] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 10/13/2020] [Indexed: 11/24/2022] Open
Abstract
Objectives: To estimate the jitter parameters (single-fiber electromyography) in myasthenia gravis patients mostly by electrical activation in Frontalis, Orbicularis Oculi, and Extensor Digitorum muscles using a concentric needle electrode. Methods: Between 2009 and 2019, a total of 97 myasthenia gravis patients, 52 male, and mean age 54 years were included. Results: Any abnormal jitter parameter in individual muscles was 90.5% (Frontalis), 88.5% (Orbicularis Oculi), and 86.6% (Extensor Digitorum). Any jitter parameter combining Orbicularis Oculi and Frontalis muscle was abnormal in 100% for the ocular, and in 92.9% for the generalized myasthenia gravis. The most abnormal muscle was Orbicularis Oculi for the generalized, and Frontalis for the ocular myasthenia gravis. The decrement was abnormal in 78.4%, 85.9% for the generalized, and 25% for the ocular myasthenia gravis. The mean jitter ranged from 14.2 to 86 μs (mean 33.3 μs) for the ocular myasthenia gravis and from 14.4 to 220.4 μs (mean 66.3 μs) for the generalized myasthenia gravis. The antibody titers tested positive in 86.6%, 91.8% for the generalized, and 50% for the ocular myasthenia gravis. Thymectomy was done in 48.5%, thymoma was found in 19.6%, and myasthenic crisis occurred by 21.6%. Conclusion: The jitter parameters achieved a 100% abnormality in ocular myasthenia gravis if both the Orbicularis Oculi and Frontalis muscles were tested. There was a high jitter abnormality in generalized myasthenia gravis cases with one muscle tested, with about a 2% increase in sensitivity when a second is added. Concentric needle electrode jitter had high sensitivity similar to the single fiber electrode (93.8%), followed by antibody titers (86.6%), and abnormal decrement (78.4%).
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Affiliation(s)
- João Aris Kouyoumdjian
- Laboratório Investigação Neuromuscular, Faculdade Estadual Medicina São José do Rio Preto, São Paulo, Brazil
| | - Gabriel Pina Paiva
- Laboratório Investigação Neuromuscular, Faculdade Estadual Medicina São José do Rio Preto, São Paulo, Brazil
| | - Erik Stålberg
- Department of Clinical Neurophysiology, Institute of Neurosciences, Uppsala University, Uppsala, Sweden
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Musa AMM, Ahmed AEM. Reference Jitter Values for Concentric Needle Electrode of Orbicularis Oculi and Frontalis Muscles Using Voluntary Activation Method in Sudanese Population. Sci Rep 2020; 10:1031. [PMID: 31974444 PMCID: PMC6978519 DOI: 10.1038/s41598-020-58037-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Accepted: 01/09/2020] [Indexed: 11/18/2022] Open
Abstract
Single fibre electromyography is the most sensitive neurophysiological test for the diagnosis of neuromuscular junction disorders, particularly myasthenia gravis. The study aimed at establishing concentric needle (CN) normal jitter values for voluntarily activated orbicularis-oculi (V-OOc) & Frontalis (V-FRO) muscles in Sudanese population. 57 healthy volunteers (20 males & 37 females) were included in the study (mean Age 43.6 ± 14.2 years, range 18–70 years). V-OOc and V-FRO were tested in the same individual using CN. Jitter values were expressed as the mean consecutive difference (MCD) of 30 potential pairs in microseconds. The mean jitter, mean individual fibre pairs jitter & mean outliers jitter values with (upper 95% Confidence Limit-CL) for [OOc] were [26.9 ± 3.3 (31.97), 26.1 ± 8.9 (41.8) & 38.5 ± 5.7 (49.0) µs] & for [FRO] were [27.1 ± 3.0 (31.32), 26.4 ± 9.4 (42.9) & 39.9 ± 5 (49.2) µs] respectively. The suggested practical upper limits for mean jitter & for outliers were (32, 49 µs) for OOc & (31, 49 µs) for FRO. Our CN-jitter values were within the range of the few published studies. The study was unique in that it established and compared between CN reference jitter values of two voluntarily activated facial muscles (V-OOc & V-FRO) in the same individual in large number of healthy subjects.
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Affiliation(s)
- Afraa M M Musa
- Department of Physiology, Faculty of Medicine, University of Khartoum, El Qasr Street, Khartoum, P.O. BOX 102, Sudan.
| | - Ammar E M Ahmed
- Department of Physiology, Faculty of Medicine, University of Khartoum, El Qasr Street, Khartoum, P.O. BOX 102, Sudan
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Pitfalls and errors in measuring jitter. Clin Neurophysiol 2017; 128:2233-2241. [DOI: 10.1016/j.clinph.2017.09.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 08/24/2017] [Accepted: 09/10/2017] [Indexed: 11/23/2022]
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Kamarajah SK, Sadalage G, Palmer J, Carley H, Maddison P, Sivaguru A. Ocular presentation of myasthenia gravis: A natural history cohort. Muscle Nerve 2017; 57:622-627. [PMID: 28881457 DOI: 10.1002/mus.25971] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2017] [Indexed: 11/07/2022]
Abstract
INTRODUCTION There are limited data on the natural history of untreated myasthenia gravis (MG) with ocular presentation. METHODS We analyzed 93 patients from symptom onset who presented to the Birmingham Midlands Eye Centre (BMEC) between January 2004 and July 2015. We used multiple stepwise logistic regression to identify predictive factors of generalization and Kaplan-Meier analysis on time to generalization. RESULTS Forty-six percent of patients developed generalized symptoms during the study period. Median time to generalization was 7 months. Time to generalization was earlier in patients seropositive for acetylcholine receptor (AChR) antibody (median 5 months vs. 21 months, P < 0.0001) and bilateral ptosis at onset (P = 0.015). Multivariate analysis identified AChR seropositivity [hazard ratio (HR) 5.03; 95% confidence interval (CI) 1.48-17.14; P = 0.001] and disease onset < 50 years (HR 3.58; 95% CI 1.18-10.90; P = 0.035) as risk factors for generalization. DISCUSSION As patients were steroid-naive before generalization, our cohort approximated the natural history of the condition. Muscle Nerve 57: 622-627, 2018.
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Affiliation(s)
- Sivesh K Kamarajah
- College of Medical and Dental Sciences, University of Birmingham, Vincent Drive, Birmingham, B15 2TT, UK
| | - Girija Sadalage
- Division of Neurology, University of Nottingham, Nottingham University Hospitals NHS Trust, Queens Medical Centre, Nottingham, UK
| | - Jonathan Palmer
- Sandwell and West Birmingham Hospitals NHS Trust, Birmingham, UK
| | - Helena Carley
- Sandwell and West Birmingham Hospitals NHS Trust, Birmingham, UK
| | - Paul Maddison
- Division of Neurology, University of Nottingham, Nottingham University Hospitals NHS Trust, Queens Medical Centre, Nottingham, UK
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Patel A, Gosk M, Pitt M. The effect of different low-frequency filters on concentric needle jitter in stimulated orbicularis oculi. Muscle Nerve 2016; 54:317-9. [DOI: 10.1002/mus.25178] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/05/2016] [Indexed: 11/10/2022]
Affiliation(s)
- Anjla Patel
- Department of Clinical Neurophysiology; Great Ormond Street Hospital For Children NHS Foundation Trust; Great Ormond Street London WC1N 3JH UK
- Department of Clinical Neurophysiology; Luton and Dunstable Hospital NHS Foundation Trust; Lewsey Road Luton LU4 0DZ UK
| | - Magdalena Gosk
- Department of Clinical Neurophysiology; Great Ormond Street Hospital For Children NHS Foundation Trust; Great Ormond Street London WC1N 3JH UK
- Department of Paediatrics; Gottfried von Preyer'sches Kinderspital; Vienna Austria
| | - Matthew Pitt
- Department of Clinical Neurophysiology; Great Ormond Street Hospital For Children NHS Foundation Trust; Great Ormond Street London WC1N 3JH UK
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Stålberg E, Sanders DB, Ali S, Cooray G, Leonardis L, Löseth S, Machado F, Maldonado A, Martinez-Aparicio C, Sandberg A, Smith B, Widenfalk J, Aris Kouyoumdjian J. Reference values for jitter recorded by concentric needle electrodes in healthy controls: A multicenter study. Muscle Nerve 2015; 53:351-62. [DOI: 10.1002/mus.24750] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 06/19/2015] [Accepted: 06/24/2015] [Indexed: 11/07/2022]
Affiliation(s)
- Erik Stålberg
- Department of Neuroscience; Clinical Neurophysiology, Uppsala University; Uppsala Sweden
| | - Donald B. Sanders
- Department of Neurology; Duke University Medical Center; Durham North Carolina USA
| | - Sajjad Ali
- Department of Clinical Neurophysiology; Queen Elizabeth Hospital Birmingham, University Hospitals Birmingham NHS Foundation Trust; Birmingham UK
| | - Gerald Cooray
- Clinical Neurophysiology, Karolinska University Hospital; Stockholm Sweden
- The Wellcome Trust for Neuroimaging, University College of London; London UK
| | - Lea Leonardis
- Institute of Clinical Neurophysiology, University Medical Center Ljubljana; Ljubljana Slovenia
| | - Sissel Löseth
- Department of Clinical Medicine; The Artic University of Norway; Tromsø Norway
- Department of Clinical Neurophysiology; University Hospital of North Norway; Tromsø Norway
| | - Flavia Machado
- Department of Neurology and Neurosurgery; Medical School, Universidade de São Paulo; São Paulo Brazil
- Fleury Medicina e Saúde; São Paulo Brazil
| | - Antonio Maldonado
- San Rafael University Hospital; Granada Spain
- Department of Clinical Neurophysiology; Ibermutuamur; Granada Spain
| | - Carmen Martinez-Aparicio
- Department of Clinical Neurophysiology; Vithas Virgen del Mar Hospital; Almeria Spain
- Doctoral Program in Clinical Medicine and Public Health; University of Granada; Granada Spain
| | - Arne Sandberg
- Department of Neuroscience; Clinical Neurophysiology, Uppsala University; Uppsala Sweden
| | - Benn Smith
- Department of Neurology, Mayo Clinic College of Medicine; Scottsdale Arizona USA
| | - Johan Widenfalk
- Department of Neuroscience; Clinical Neurophysiology, Uppsala University; Uppsala Sweden
- Department of Neuroscience; Karolinska Institutet; Stockholm Sweden
| | - João Aris Kouyoumdjian
- Neuromuscular Investigation Laboratory; Faculdade Medicina São José do Rio Preto; São Paulo Brazil
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Jitter analysis with concentric needle electrodes in the extensor digitorum communis for the diagnosis of myasthenia gravis: a pilot study. Chin Med J (Engl) 2014. [DOI: 10.1097/00029330-201409200-00003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Reference values in concentric needle electrode studies. Clin Neurophysiol 2013; 124:1255-6. [DOI: 10.1016/j.clinph.2012.09.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2012] [Revised: 09/22/2012] [Accepted: 09/25/2012] [Indexed: 11/20/2022]
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Abstract
Because of certain restrictions in medical praxis, reusable materials are only allowed in some countries. This also applies to electrodes for electromyography; the special single-fiber electromyography electrode must be replaced. This article gives some details of the possibilities of using an alternative-a small concentric needle electrode. Practical hints, reference values, and the application in diagnostic work for myasthenia gravis are summarized.
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Affiliation(s)
- Erik Stålberg
- Department of Clinical Neurophysiology, Uppsala University, Sweden.
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Kouyoumdjian JA, Stålberg E. Stimulated jitter with concentric needle in 42 myasthenia gravis patients. ARQUIVOS DE NEURO-PSIQUIATRIA 2013; 71:237-43. [DOI: 10.1590/0004-282x20130008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 10/26/2012] [Indexed: 11/22/2022]
Abstract
Objective: To estimate jitter parameters in myasthenia gravis in stimulated frontalis and extensor digitorum muscles using the concentric needle electrode. Methods: Forty-two confirmed myasthenia gravis patients, being 22 males (aged 45.6±17.2 years-old) were studied. Jitter was expressed as the mean consecutive difference (MCD). Results: MCD in extensor digitorum was 61.6 µs (abnormal in 85.7%) and in frontalis 57.3 µs (abnormal in 88.1%). Outliers represented 90.5% for extensor digitorum and 88.1% for frontalis. At least one jitter parameter was abnormal in 90.5% of the combined studies. Acetylcholine receptor antibody was abnormal in 85.7% of the cases. Conclusions: Stimulated jitter recordings measured from muscles using concentric needle electrode can be used for myasthenia gravis diagnosis with high sensitivity. Extensive normative studies are still lacking and, therefore, borderline findings should be judged with great caution.
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Affiliation(s)
- João Aris Kouyoumdjian
- Faculdade de Medicina de São José do Rio Preto (FAMERP); Neuromuscular Investigation Laboratory, Brazil
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Kouyoumdjian JA, Stålberg EV. Concentric needle jitter on voluntary activated frontalis in 20 healthy subjects. Muscle Nerve 2013; 47:440-2. [DOI: 10.1002/mus.23710] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/22/2012] [Indexed: 11/11/2022]
Affiliation(s)
- João A. Kouyoumdjian
- Faculdade de Medicina de São José do Rio Preto (FAMERP); Department of Neurological Sciences; Rua Luiz Antônio da Silveira 1661 15025-020 São José do Rio Preto São Paulo Brazil
| | - Erik V. Stålberg
- Department of Clinical Neurophysiology; University Hospital; Institute of Neuroscience Uppsala University; Uppsala Sweden
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Affiliation(s)
- Donald B. Sanders
- Neuromuscular Section; Division of Neurology; Duke University Medical Center; Durham North Carolina 27710 USA
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Abstract
This article reviews the use of electrodiagnostic testing in disorders of neuromuscular transmission and discusses the differences between various presynaptic and postsynaptic disorders. Attention is paid to quality control issues that influence the sensitivity of repetitive nerve stimulation and single fiber electromyography. Electrodiagnostic testing, when used as an extension of the clinician's history and physical examination, will provide appropriate direction in establishing the diagnosis.
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Affiliation(s)
- James F Howard
- Neuromuscular Disorders Section, Department of Neurology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7025, USA.
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