Referenced in: none

Automatically associated channels: Kir2.3

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

Authors: Jeffrey M Statland, Brian N Bundy, Yunxia Wang, Jaya R Trivedi, Dipa Raja Rayan, Laura Herbelin, Merideth Donlan, Rhonda McLin, Katy J Eichinger, Karen Findlater, Liz Dewar, Shree Pandya, William B Martens, Shannon L Venance, Emma Matthews, Anthony A Amato, Michael G Hanna, Robert C Griggs, Richard J Barohn,

Journal, date & volume: Muscle Nerve, 2012 Oct , 46, 482-9

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/22987687

Abstract
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.