Type B3胸腺腫を合併した抗gamma aminobutyric acid （GABA）A受容体抗体陽性再発性脳炎の1例

A 87-year-old female presented with subacute progression of cognitive decline. Fluid-attenuated inversion recovery images of brain MRI showed multifocal high-intensity lesions. Thoracic CT image revealed the presence of thymoma, and serum autoantibody screening showed positivity for anti-gamma aminobutyric acid (GABA)A receptor antibody. Histopathological analysis confirmed type B3 thymoma after thymectomy. The patient received both plasmapheresis and intravenous methylprednisolone therapy, and showed remarkable amelioration of clinical symptoms and MRI abnormal high intensity. However, after 2 month from the clinical recovery, the patient showed recurrence of brain lesions and intravenous methylprednisolone monotherapy was performed. Continuation of oral steroid therapy was required to maintain the quienscent state of inflammation within the central nervous system. Anti-GABAA receptor antibody is a recently discovered novel autoantibody associated with autoimmue encephalitis. Due to the limited number of literature reported, clinical course and therapeutic response of GABAA receptor antibody encephalitis remains elusive. Here we reported a rare case of GABAA receptor antibody encephalitis with type B3 thymoma. Clinical, radiological and therapeutic courses described in our report highlight the importance of immunotherapy for treatment of the disease.