Chapter 28 Clinical electrophysiologic tests and genotype correlations in muscle channelopathies

Abstract

Publisher Summary This chapter discusses the clinical electrophysiologic tests used in muscle channelopathies. In clinical neurophysiology, myotonic discharges may occur with or without clinical myotonia and are qualitatively the same regardless of the involved channels. Myotonic discharges take two forms, depending on the spatial relationship between the recording area and the discharging muscle fibers. A combined study utilizing electromyography, 10 Hz repetitive nerve stimulation, short exercise test with cooling, and prolonged exercise test may differentiate Na+ channelopathies from Cl– channelopathies. The prolonged exercise test is the most sensitive and useful electrophysiologic test in periodic paralysis (PP). Patients exhibit cardiac dysrhythmias reminiscent of the long QT syndrome, ranging from the nonsymptomatic prolongation of the QT interval to cardiac arrest. Hence, electrocardiographic abnormalities in association with periodic paralysis may be predictive of this syndrome. Thus, a combined study of electromyography and prolonged exercise test may differentiate Na+ channelopathies and Ca++ channelopathies in PP.