Muscle ultrasound measurements and functional muscle parameters in non-dystrophic myotonias suggest structural muscle changes

Abstract Patients with non-dystrophic myotonias, including chloride (myotonia congenita) and sodium channelopathies (paramyotonia congenita/potassium aggravated myotonias), may show muscular hypertrophy in combination with some histopathological abnormalities. However, the extent of muscle changes has never been assessed objectively in a large group genetically confirmed patients. This study quantitatively determines echo intensities, thicknesses, ranges-of-motion and force of four skeletal muscles in 63 genetically confirmed patients. The main findings revealed elevated echo intensities in all muscles except the rectus femoris (+1.3–2.2 SD, p p r  = −0.43; p r  = −0.47; p r  = −0.40; p  = 0.001, and tibial anterior: r  = −0.27; p  = 0.04) and correlated positively to age ( r  = 0.22; p  = 0.05). The echo intensity of the forearm flexors was inversely correlated to their muscles’ force ( r  = −0.30; p  = 0.02). Together, these data suggest that non-dystrophic myotonias may lead to structural muscle changes.