A case of autoantibody-negative autoimmune encephalitis associated with mature ovarian teratoma, successfully treated with early ovariectomy

An 18-year-old woman was admitted to our hospital with altered consciousness and urinary retention. Brain MRI revealed FLAIR hyperintensity along the brainstem surface. Paraneoplastic encephalitis was suspected due to the presence of an ovarian teratoma, and an ovariectomy was performed on the day of admission. Both steroid pulse therapy and high-dose intravenous immunoglobulin therapy were initiated, leading to an improvement in her clinical symptoms and MRI findings. All tested autoantibodies were negative. There have been no reports on the optimal timing of ovariectomy in cases of autoimmune encephalitis associated with ovarian teratoma, except in anti-N-methyl-D-aspartate receptor encephalitis. However, early tumor resection may be desirable for antigen removal, even in cases of autoimmune encephalitis without anti-N-methyl-D-aspartate receptor antibody.