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Muscle Nerve. 2012 Oct;46(4):482-9. doi: 10.1002/mus.23402.

A quantitative measure of handgrip myotonia in non-dystrophic myotonia.

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  • 1Department of Neurology, University of Rochester Medical Center, Rochester, New York, USA.



Non-dystrophic myotonia (NDM) is characterized by myotonia without muscle wasting. A standardized quantitative myotonia assessment (QMA) is important for clinical trials.


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.


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.


QMA is an automated, non-invasive technique for evaluating myotonia in NDM.

Copyright © 2012 Wiley Periodicals, Inc.

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