Objective:

To report a rare case of thymoma-associated Morvan’s syndrome developing years after myasthenia gravis, highlighting that overlapping symptoms can delay diagnosis, and emphasizing the importance of comprehensive antibody evaluation and electrophysiologic studies to uncover additional paraneoplastic disorders.

Background:

Morvan’s syndrome (MoS) is a rare autoimmune disorder, characterized by peripheral nerve hyperexcitability, autonomic dysfunction and neuropsychiatric manifestations such as insomnia and hallucinations. The condition is most frequently associated with antibodies against contactin-associated protein-like 2 (CASPR2), and has a strong paraneoplastic association with thymoma. Thymic tumors can induce a spectrum of autoimmune responses, among which myasthenia gravis (MG) is the most common. The coexistence of MoS and MG reflects the shared thymoma-driven immune dysregulation, but is distinctly uncommon. When MoS develops years after established MG, early manifestations like twitching, fatigue, or insomnia may be misattributed to drug effects or myasthenic symptoms making diagnosis challenging. 

Design/Methods:

A 35-year-old man with thymoma-associated acetylcholine receptor antibody-positive MG diagnosed three years earlier and managed with mycophenolate mofetil, presented with three months of progressively worsening back pain, diffuse pruritus, muscle twitching, severe insomnia, and visual hallucinations. Examination showed diffuse muscle rippling, fasciculations, and weakness without fatigability. Autonomic dysfunction was evident with persistent severe hypertension, hyponatremia and recurrent hyperhidrosis. Electromyography revealed continuous neuromyotonic discharges and paraneoplastic antibody testing was positive for CASPR2 and negative for LGI1. These findings supported the diagnosis of thymoma-associated Morvan’s syndrome. The patient was treated with high dose intravenous methylprednisolone followed by a five-day course of intravenous immunoglobulin, with marked symptomatic improvement.

Results:

N/A

Conclusions:

This case demonstrates that thymoma may precipitate multiple autoimmune syndromes beyond myasthenia gravis, reminding clinicians that new neuromuscular or autonomic symptoms warrant reevaluation for paraneoplastic syndromes where early recognition and immunotherapy can significantly improve outcomes and quality of life.