Morvan syndrome in a patient with progressing metastatic thymoma and myasthenia gravis

Morvan syndrome (MoS) is a rare paraneoplastic syndrome that is predominantly characterised by autonomic dysfunction, peripheral nerve hyperexcitability and altered mental status. Cases in literature often describe pre-existing autoimmune diagnoses in patients with MoS, alluding to its association with systemic immune dysregulation.We report a woman presenting with hypersomnolence and fluctuating mental status consistent with MoS who had been previously diagnosed with metastatic thymoma, acetylcholine receptor-positive myasthenia gravis and multiple other chronic medical conditions. The report emphasises the importance of prompt recognition of symptoms and accurate diagnosis in rare diseases, allowing for timely initiation of the appropriate immunotherapy that ultimately led to rapid and significant clinical improvement.