A case of paraneoplastic limbic encephalitis caused by mature cystic teratoma

Paraneoplastic Limbic Encephalitis (PLE) is a kind of limbic encephalitis caused by remote effects of tumors. It is caused by immune reaction to antigens common in tumors and nerve tissue. We report a case which was suspected to be limbic encephalitis and in which the clinical symptoms improved after operation. The patient was a 69-year-old woman, G0P0, who suffered from depression and weight loss. She presented to the psychiatry department in another hospital and was then referred to the neurology department in our hospital because of acute cognitive dysfunction and higher brain dysfunction. Brain MRI showed mild ischemic changes without space-occupying lesion or cerebrovascular disease. Cerebrospinal fluid examination showed no evidence of infectious encephalitis. At this point, immune encephalitis was suspected and whole- body computer tomographic (CT) scan was performed. On CT scan, an ovarian cyst was found on the right side, so she was diagnosed with clinical paraneoplastic limbic encephalitis. After consultation with the gynecology department, we examined her serum N- Methyl-D-Aspartate (NMDA) receptor antibody and performed bilateral laparoscopic adnexectomy. Pathological examination suggested mature cystic teratoma in the right ovary and fibroma in the left ovary, however, the serum NMDA receptor antibody was negative. After the operation, her cognitive function and higher brain function improved immediately on postoperative day one. After six months, she became independent in everyday life. We, therefore, diagnosed this case as clinically paraneoplastic limbic encephalitis. In conclusion, when limbic encephalitis is suspected, the possibility of paraneoplastic limbic encephalitis should be considered and whole-body CT is strongly recommended. Surgical resection should be considered when ovarian cyst is found, even if NMDA receptor antibody is negative.