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J Child Neurol. 2015 Sep;30(10):1300-6. doi: 10.1177/0883073814559646. Epub 2015 Jan 30.

Use of Clinical and Electrical Myotonia to Differentiate Childhood Myopathies.

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Department of Neurology, Mayo Clinic, Rochester, MN, USA Department of Neurology, Boston Children's Hospital, Boston, MA, USA.
Department of Neurology, Mayo Clinic, Rochester, MN, USA


We retrospectively reviewed 2030 childhood electromyograms performed over an 11-year period (2004-2014). Twenty children (1%) with myotonic discharges were identified and placed into 2 groups. Group A (electrical and clinical myotonia) comprised 9 children (8 with myotonia congenita and 1 with paramyotonia congenita); all of them had diffuse myotonic discharges without clinical weakness or elevated creatine kinase. Group B (electrical myotonia without clinical myotonia) comprised 11 children (4 with inflammatory myopathy; 3, congenital myopathy, 3, muscular dystrophy; and 1, congenital muscular dystrophy). Clinical weakness was demonstrated in all of them and elevated creatine kinase in 6; all had a myopathic electromyogram and scattered myotonic discharges. We conclude that myotonic discharges are a rare but characteristic spontaneous discharge identified during electrodiagnostic studies in children. The presence of electrical and clinical myotonia provides helpful clues to differentiate between various muscle disorders in children.


children; electromyography; muscle disorders; myotonia; myotonic discharges

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