Treatment of Myotonia - Lamotrigine Versus Namuscla

In this clinical study, the aim is to investigate whether there is a difference in treatment of myotonia using two drugs. A difference there can justify the significantly higher cost when treated by Namuscla versus Lamotrigine.According to the current corona pandemic, the investigators designed an app to use for data collection in the study. The app also ensures that patients who live far from the clinic more easily can participate.

Inclusion Criteria:Capable adult women and men (age ≥ 18 years).Diagnosed with Myotonia Congenita (Becker and Thomsen type), Paramyotonia Congenita, or Hyperkalemic periodic paralysis.Myotonia under treatment or which significantly limits the daily activities (MBS> 2).Exclusion Criteria:Allergy to lamotrigine, mexiletine, or the inactive ingredients in trial medication.Disease, which is affected by trial medication such as heart disease (ischemia and arrhythmia), epilepsy, and significant renal or hepatic failure.Treatment that, in the opinion of the project manager, can affect the study result - medication with significant interactions with trial medication.In case of smoking, start or cessation during the study.Pregnant or breastfeeding during the study period. Fertile women with a positive pregnancy test at the time of entry into the trial, or who do not use safe contraception during the project period.