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A quantitative measure of handgrip myotonia in non‐dystrophic myotonia
Author(s) -
Statland Jeffrey M.,
Bundy Brian N.,
Wang Yunxia,
Trivedi Jaya R.,
Raja Rayan Dipa,
Herbelin Laura,
Donlan Merideth,
McLin Rhonda,
Eichinger Katy J.,
Findlater Karen,
Dewar Liz,
Pandya Shree,
Martens William B.,
Venance Shan L.,
Matthews Emma,
Amato Anthony A.,
Hanna Michael G.,
Griggs Robert C.,
Barohn Richard J.
Publication year - 2012
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.23402
Subject(s) - myotonia , medicine , relaxation (psychology) , myotonic dystrophy , endocrinology
Abstract Introduction: Non‐dystrophic myotonia (NDM) is characterized by myotonia without muscle wasting. A standardized quantitative myotonia assessment (QMA) is important for clinical trials. Methods: Myotonia was assessed in 91 individuals enrolled in a natural history study using a commercially available computerized handgrip myometer and automated software. Average peak force and 90% to 5% relaxation times were compared with historical normal controls studied with identical methods. Results: Thirty subjects had chloride channel mutations, 31 had sodium channel mutations, 6 had DM2 mutations, and 24 had no identified mutation. Chloride channel mutations were associated with prolonged first handgrip relaxation times and warm‐up on subsequent handgrips. Sodium channel mutations were associated with prolonged first handgrip relaxation times and paradoxical myotonia or warm‐up, depending on underlying mutations. DM2 subjects had normal relaxation times but decreased peak force. Sample size estimates are provided for clinical trial planning. Conclusion: QMA is an automated, non‐invasive technique for evaluating myotonia in NDM. Muscle Nerve 46: 482–489, 2012