Morvan Syndrome Converted from Isaacs' Syndrome after Thymectomy with Positivity for Both Anti-LGI1 and Anti-CASPR2 Antibodies

Anti-voltage-gated potassium channel complex antibodies-mediated disorder includes Isaacs'' syndrome, which is characterized by neuromyotonia, and Morvan syndrome, which is characterized by neuromyotonia, encephalopathy and autonomic dysfunction. We herein report a patient with Morvan syndrome that converted from Isaacs'' syndrome after thymectomy. The patient first presented with myospasm in all extremities and positivity for both anti-leucine-rich glioma inactivated 1 (LGI1) and anti-contactin-associated protein like 2 (CASPR2) antibodies and subsequently developed encephalopathy after thymectomy, which was successfully improved by immunotherapy. This is the first case of Morvan syndrome wherein thymectomy worsened Isaacs'' syndrome, suggesting that immunotherapy should be considered for Isaacs'' syndrome accompanied by positivity for both anti-LGI1 and anti-CASPR2 antibodies to prevent worsening to Morvan syndrome.