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Concentric and single fiber needle electrodes yield comparable jitter results in myasthenia gravis

Authors

  • Maria E. Farrugia DPhil, MD,

    Corresponding author
    1. Neurology Department, Institute of Neurological Sciences, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, United Kingdom
    • Neurology Department, Institute of Neurological Sciences, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, United Kingdom
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  • Andrew I. Weir MSc, MBChB,

    1. Clinical Neurophysiology Department, Institute of Neurological Sciences, Southern General Hospital, Glasgow G51 4TF, United Kingdom
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  • Marie Cleary PhD,

    1. Orthoptic Department, Gartnavel General Hospital, Glasgow G12 0YN, United Kingdom
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  • Sarah Cooper MD,

    1. Neurology Department, Institute of Neurological Sciences, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, United Kingdom
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  • Richard Metcalfe MD,

    1. Neurology Department, Institute of Neurological Sciences, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, United Kingdom
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  • Arup Mallik BSc, MBChB

    1. Clinical Neurophysiology Department, Institute of Neurological Sciences, Southern General Hospital, Glasgow G51 4TF, United Kingdom
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Abstract

The single fiber needle electrode (SFNE), which is designed to isolate single muscle fiber action potentials, has played an important role in the diagnosis of myasthenia gravis (MG). However, the concentric needle electrode (CNE) has been recently adopted by some workers to study neuromuscular instability in MG, and reference data have also been obtained in healthy subjects. In this study we wanted to establish whether data acquired using the SFNE is comparable to that obtained using the CNE when studying patients with MG. We established reference data for our laboratory using the CNE for orbicularis oculi (OO) and extensor digitorum communis (EDC). We compared data from 24 MG patients using both SFNE and CNE and found no significant differences in mean jitter values for either muscles. We correlated the neurophysiological data obtained by either electrode with various clinical assessments, the ice pack test, OO and EDC strength measurement, and MGFA classification of disease, and we found no significant relation. We compared discomfort scores for the two needle electrodes for each muscle and found that the discomfort scores for CNE are significantly lower (P = 0.0004). We conclude that the CNE is a useful alternative electrode for studying single fiber potentials, but more reference data from normal control subjects is desirable. Muscle Nerve, 2008

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