Dual anti-LGI1/CASPR2 antibody-positive Morvan’s syndrome with B2 thymoma achieving complete remission after thymectomy: a case report

Morvan’s syndrome is a rare autoimmune disorder defined by peripheral nerve hyperexcitability, autonomic dysfunction, and central nervous system involvement. While its association with thymoma and antibodies against LGI1 and CASPR2 is established, dual antibody positivity is uncommon and poses distinct diagnostic and therapeutic challenges. A 73-year-old Han Chinese man presented with a 15-day history of muscle twitching, profuse sweating, insomnia, and visual hallucinations. Electromyography confirmed neuromyotonia. Serum testing returned positive for both anti-LGI1 (titer 1:10) and anti-CASPR2 (titer 1:32) antibodies. Contrast-enhanced chest CT identified an anterior mediastinal mass, which was completely resected and confirmed as a World Health Organization type B2 thymoma on histology. While intravenous immunoglobulin yielded only partial improvement, complete neurological remission was observed within 4 weeks following thymectomy. Antibodies remained detectable at the 12-month follow-up, but the patient has remained relapse-free without further immunotherapy. This case provides three key learning points: firstly, it underscores the critical importance of systematic thymoma screening in Morvan’s syndrome; secondly, it demonstrates that durable clinical remission can be achieved without seroconversion, guiding post-operative monitoring; and thirdly, it suggests that in dual antibody-positive patients with an incomplete response to immunotherapy, early thymectomy may be considered as a potential therapeutic option.