To report a case of CASPR2-antibody associated Morvan syndrome manifesting after thymectomy of a malignant thymoma, in the absence of thymoma recurrence, and in association with a pancreatic neuroendocrine tumor. To our knowledge, this is the first case report of such an association.

CASPR2-antibody associated Morvan Syndrome is known to cause profound peripheral, autonomic, and central nervous system dysfunction, but remains poorly recognized by clinicians. It can be associated with underlying tumors, most commonly thymomas. Early recognition and prompt treatment is important given the debilitating nature of the disease and its response to tumor removal and/or immunotherapy. 

We present the case of a 53-year-old man with subacute onset of severe, debilitating hyperhidrosis, neuropathic pain, cramps, insomnia, and weight loss approximately 1 year after being diagnosed with acetylcholine receptor antibody positive ocular myasthenia gravis in the setting of a malignant, invasive thymoma. He underwent thymectomy and radiation therapy with remission of thymoma and all ocular symptoms for approximately 1 year before developing symptoms of Morvan Syndrome. Work up revealed positive serum and CSF CASPR2-IgG and positive serum LGI1-IgG antibodies. Electromyography revealed fasciculations and myokymia. Work up was negative for thymoma recurrence, but did reveal a pancreatic lesion that was later biopsy-proven to be a pancreatic neuroendocrine tumor. Treatment with intravenous immunoglobulin and plasmapheresis failed to result in any clinical improvement. He was ultimately treated with Rituximab with complete symptomatic resolution.

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Typically, the development of Morvan syndrome leads to the diagnosis of thymoma that is subsequently treated with thymectomy. This case illustrates that it can occur after thymectomy in the absence of thymoma recurrence. It also emphasizes the importance of a broad work up of underlying tumors, given there have not been reports of Morvan syndrome in the setting of a pancreatic neuroendocrine tumor.