Myotonia is often a painful and disabling symptom which can interfere with daily motor function resulting in significant morbidity. Since
myotonic disorders are rare it has generally proved difficult to obtain class I level evidence for anti-myotonic
drug efficacy by performing randomized placebo controlled trials. Current treatment guidance is therefore largely based on anecdotal reports and physician experience. Despite the genetic channel heterogeneity of the
myotonic disorders the
sodium channel antagonists have become the main focus of pharmacological interest.
Mexiletine is currently regarded as the first choice
sodium channel blocker based on a recent placebo controlled randomized trial. However, some patients do not respond to
mexiletine or have significant side effects limiting its use. There is a clinical need to develop additional antimyotonic agents. The study of Desaphy et al. is therefore important and provides in vitro evidence that a number of existing drugs with
sodium channel blocking capability could potentially be repurposed as anti-myotonic drugs. Translation of these potentially important in vitro findings into clinical practice requires carefully designed randomized controlled trials. Here we discuss Desaphy's findings in the wider context of attempts to develop additional
therapies for patients with clinically significant
myotonia.