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February 01, 2022; 98 (5) Resident & Fellow Section

Teaching Video NeuroImage: Myokymia on Muscle Ultrasound in Radiation-Induced Brachial Plexopathy

Michaël T.J. Peeters, Nadia A. Sutedja, Martinus P.G. Broen
First published October 29, 2021, DOI: https://doi.org/10.1212/WNL.0000000000013019
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A 65-year-old women presented with right arm weakness and paresthesia. She had undergone radiotherapy for a supraclavicular metastasized lung cancer 8 years ago. Examination revealed weakness, wasting, and wavelike involuntary contractions in the right deltoid, triceps, and dorsal interossei muscles. EMG confirmed a brachial plexopathy with additional myokymic discharges. Spontaneous semirhythmic contractions with a rotatory or to-and-fro component were seen on muscle ultrasound, compatible with myokymia (Video 1).

Video 1

Clinical, EMG, and ultrasound findings compatible with myokymia. Part I: Examination reveals involuntary, wavelike contractions of the right deltoid muscle. Part II: EMG demonstrated grouped repetitive spontaneous discharges within the same motor unit with a sound resembling marching soldiers. Part III: ultrasound shows semirhythmic contractions with a rotatory component. These findings are characteristic for myokymia.Download Supplementary Video 1 via http://dx.doi.org/10.1212/013019_Video_1

Myokymic discharges indicate radiation-induced plexopathy rather than tumor recurrence or other plexopathy forms, probably because myokymia arises from radiation-induced membrane instability and ectopic neural activity. Muscle ultrasound is a promising noninvasive tool for its detection, complementary to EMG.1,2

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The authors report no targeted funding.

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The authors report no disclosures relevant to the manuscript. Go to Neurology.org/N for full disclosures.

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References

  1. 1.↵
    1. Harper CM Jr.,
    2. Thomas JE,
    3. Cascino TL,
    4. Litchy WJ
    . Distinction between neoplastic and radiation-induced brachial plexopathy, with emphasis on the role of EMG. Neurology. 1989;39(4):502-506.
    OpenUrlAbstract/FREE Full Text
  2. 2.↵
    1. Pelosi L,
    2. Galley I
    . Radiation induced subclinical brachial myokymia captured on muscle ultrasound. Clin Neurophysiol. 2020;131(5):1166-1167.
    OpenUrl

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