Myelin basic protein expression in thymoma after methylprednisolone administration for multiple sclerosis

The relationship between thymic epithelial tumour and demyelinating disease (DD) is unknown and surgical resection has not been optimized. A 39‐year‐old woman was administrated methylprednisolone for newly diagnosed multiple sclerosis. A thymic tumour was found in the antero‐superior mediastinum via computed tomography of the chest. Video‐assisted thoracoscopic thymectomy was performed. Histologically, the tumour was diagnosed as Type AB thymoma. Immunohistochemical staining showed positive myelin basic protein (MBP) in the cytosol of spindle cells in the tumour specimen. Germinal centres or lymphocytes infiltration were not noted. Ectopic MBP presentation in thymoma might be correlated with DD.