Comparative efficacy of repetitive nerve stimulation, exercise, and cold in differentiating myotonic disorders

• Published in: Muscle & nerve Vol. 36; no. 5; pp. 643 - 650
• Main Authors: Michel, Patrik, Sternberg, Damien, Jeannet, Pierre-Yves, Dunand, Murielle, Thonney, Francine, Kress, Wolfram, Fontaine, Bertrand, Fournier, Emmanuel, Kuntzer, Thierry
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.11.2007; Wiley
• Subjects: Action Potentials - genetics; Action Potentials - physiology; Action Potentials - radiation effects; Adult; Biological and medical sciences; Chloride Channels - genetics; cold; Cold Temperature; Development. Senescence. Regeneration. Transplantation; Diseases of striated muscles. Neuromuscular diseases; DNA Mutational Analysis; Dose-Response Relationship, Radiation; Electric Stimulation - methods; Electromyography - methods; Exercise; Female; Fundamental and applied biological sciences. Psychology; Humans; Male; Medical sciences; Middle Aged; muscle channelopathies; Muscle, Skeletal - physiopathology; Muscle, Skeletal - radiation effects; Mutation - physiology; mutations; myotonia; Myotonic Disorders - classification; Myotonic Disorders - diagnosis; Myotonic Disorders - genetics; Myotonic Disorders - physiopathology; Neurology; Reaction Time - genetics; Reaction Time - radiation effects; repetitive nerve stimulation; Statistics, Nonparametric; temperature; Vertebrates: nervous system and sense organs; Human; Neuromuscular diseases; Nervous system diseases; Temperature; Cooling; Myotonia; Electrophysiology; Paramyotonia; Action potential; cold; muscle channelopathies; Sodium chloride; repetitive nerve stimulation; Genetic disease; Rest; mutations; Myotonic dystrophy; Repetitive stimulus; Muscle; Mutation
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/mus.20856

The decremental response of the compound muscle action potential (CMAP) to provocative tests is not characterized in genetically verified myotonic disorders. We therefore studied the relationship between decremental responses and mutation type in 10 patients with recessive myotonia congenita (rMC), two with paramyotonia congenita (PMC), nine with myotonic dystrophy type 1 (DM1), four with DM2, and 14 healthy people. CMAPs were measured at rest, just after a short exercise test (SET), and during short, 5‐ and 10‐HZ, repetitive nerve stimulation (RNS) trains at 32°C and at 20°C. The degree of decrement was not related to the severity of clinical myotonia. Controls and PMC patients had similar responses when warm, but with cooling PMC patients had a persistent decrement of CMAPs. In the rMC patients the decremental responses were related to the type of mutation of the CLCN1 gene, as a decrement was encountered in the T268M, R894X, IVS17+1 G>T, K248X, and 2149 del G, but not with the IVS1+3 A>T, F167L, or dominant A313T mutations. In DM1 patients there was no relationship between decrement and CTG repeats. The degree of partial inexcitability in myotonic muscle membrane therefore depends on the mutation type rather than degree of clinical myotonia. RNS at 10 HZ is more sensitive than SET for demonstrating abnormalities in rMC patients when warm; differences are less marked when cold, which is useful to diagnose PMC. Provocative tests are therefore useful in myotonias to demonstrate muscle inexcitability, which depends on the chloride or sodium channelopathy. Muscle Nerve, 2007