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

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 < 0.0001), and hypertrophy in the arms (+0.5–0.9 SD, p < 0.01). Muscle echo intensities were inversely correlated to the corresponding ranges-of-motion (biceps brachii: r = −0.43; p < 0.001, forearm flexors: r = −0.47; p < 0.001, rectus femoris: 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.