Abstract | OBJECTIVE: To improve the accuracy of genotype prediction and guide genetic testing in patients with muscle channelopathies we applied and refined specialized electrophysiological exercise test parameters. METHODS: We studied 56 genetically confirmed patients and 65 controls using needle electromyography, the long exercise test, and short exercise tests at room temperature, after cooling, and rewarming. RESULTS: Concordant amplitude-and-area decrements were more reliable than amplitude-only measurements when interpreting patterns of change during the short exercise tests. Concordant amplitude-and-area pattern I and pattern II decrements of >20% were 100% specific for paramyotonia congenita and myotonia congenita, respectively. When decrements at room temperature and after cooling were <20%, a repeat short exercise test after rewarming was useful in patients with myotonia congenita. Area measurements and rewarming distinguished true temperature sensitivity from amplitude reduction due to cold-induced slowing of muscle fiber conduction. In patients with negative short exercise tests, symptomatic eye closure myotonia predicted sodium channel myotonia over myotonia congenita. Distinctive "tornado-shaped" neuromyotonia-like discharges may be seen in patients with paramyotonia congenita. In the long exercise test, area decrements from pre-exercise baseline were more sensitive than amplitude decrements-from-maximum-compound muscle action potential (CMAP) in patients with Andersen-Tawil syndrome. Possible ethnic differences in the normative data of the long exercise test argue for the use of appropriate ethnically-matched controls. INTERPRETATION: Concordant CMAP amplitude-and-area decrements of >20% allow more reliable interpretation of the short exercise tests and aid accurate DNA-based diagnosis. In patients with negative exercise tests, specific clinical features are helpful in differentiating sodium from chloride channel myotonia. A modified algorithm is suggested.
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Authors | S Veronica Tan, Emma Matthews, Melissa Barber, James A Burge, Sanjeev Rajakulendran, Doreen Fialho, Richa Sud, Andrea Haworth, Martin Koltzenburg, Michael G Hanna |
Journal | Annals of neurology
(Ann Neurol)
Vol. 69
Issue 2
Pg. 328-40
(Feb 2011)
ISSN: 1531-8249 [Electronic] United States |
PMID | 21387378
(Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
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Copyright | Copyright © 2011 American Neurological Association. |
Topics |
- Adolescent
- Adult
- Aged
- Channelopathies
(diagnosis, genetics)
- Electromyography
- Exercise Test
- Female
- Humans
- Male
- Middle Aged
- Muscle Weakness
(diagnosis, genetics)
- Muscle, Skeletal
(pathology)
- Myotonic Disorders
(diagnosis, genetics)
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