Abstract
A 74-year-old gentleman was admitted to the regional neurosciences center with encephalopathy, myokymia, and dysautonomia. Chest imaging had previously identified an incidental mass in the anterior mediastinum, consistent with a primary thymic tumor. Antivoltage-gated potassium channel (anti-VGKC) antibodies were positive (titer 1273 pmol/L) and he was hypokalemic. Electromyogram and nerve conduction studies were in keeping with peripheral nerve hyperexcitability syndrome, and an electroencephalogram was consistent with encephalopathy. A diagnosis of Morvan syndrome was made, for which he was initially treated with high-dose steroids, followed by a 5-day course of intravenous immunoglobulin (IVIG) therapy. He also underwent thymectomy, followed by a postexcision flare of his symptoms requiring intensive care management. Further steroids, plasmapheresis, and IVIG achieved stabilization of his clinical condition, enabling transfer for inpatient neurorehabilitation. He was commenced on azathioprine and a prolonged oral steroid taper. A subsequent presumed incipient relapse responded well to further IVIG treatment. This case report documents a thymoma-associated presentation of anti-VGKC-positive Morvan syndrome supplemented by patient and carer narrative and video, both of which provide valuable further insights into this rare disorder. There are a limited number of publications surrounding this rare condition available in the English literature. This, combined with the heterogenous presentation, association with underlying malignancy, response to treatment, and prognosis, provides a diagnostic challenge. However, the association with anti-VGKC antibody-associated complexes and 2 recent case series have provided some scope for both accurate diagnosis and management.