WL Lau, CH Ko, HHC Lee, CM Mak

Abstract

Non-dystrophic myotonia (NDMs) is a group of heterogenous skeletal muscle channelopathies. This entity is rare but potentially treatable. We reported two children with NDMs, namely myotonia congenita and paramyotonia congenita. The first child presented with abnormal gait with difficulty to initiate movement. The second child had stiffness and gait abnormality precipitated by cold weather. Needle electromyography demonstrated myotonic discharges in both cases. Diagnosis was confirmed by identifying mutations in CLCN1 and SCN4A genes respectively. The first patient had favourable response to treatment with mexiletine. The second child had mild symptoms controlled with pro re nata carbamazepine.