Limbic encephalitis with anti‐GAD antibodies and Thomsen myotonia: a casual or causal association?

The association between hereditary myotonic disorders and epilepsy is seldom described in the literature. To date, few reports have dealt with dystrophic myotonias, whereas a single case demonstrating an association between sporadic congenital myotonia and epilepsy was recently reported in a patient carrying a de novo mutation of the CLCN1 gene. Additional evidence for a role of CLCN1 in the pathogenesis of epilepsy is derived from large‐scale exome analysis of ion channel variants and expression studies. Here, we describe the first case of association between familial Thomsen myotonia and epilepsy. All the affected members of a two‐generation family presented myotonia and disclosed a pathogenic mutation in CLCN1 . In addition, one individual experienced epileptic seizures due to limbic encephalitis (LE) with anti‐GAD antibodies. The occurrence of the two diseases in this patient could be a chance association, however, CLCN1 mutation, as a susceptibility factor for epilepsy through dysfunction of GABA a inhibitory signalling, cannot be ruled out as a possible influence.