[A case of limbic encephalitis with small cell lung carcinoma in which the cognitive function improved and redeteriorated during tumor therapy].

We report the findings regarding a 70-year-old man with paraneoplastic limbic encephalitis. He presented with a chief complaint of inability to recall any events. He had been well until one month before admission, and then he abruptly began to show progressive amnesia. At admission, the patient's score on the Revised Hasegawa Dementia Scale (HDS-R) showed a decline to 13/30, thus indicating the existence of severe disorientation and an impaired memory. The brain CT and EEG showed no specific abnormalities and an analysis of cerebrospinal fluid showed only a mild increase in the total protein level. A chest X-ray film revealed a mass in the right hilum, while a histological analysis of the biopsied specimen finally established a diagnosis of small cell lung carcinoma. The FDG-PET and the enhanced brain MRI showed a single small metastatic lesion in the cerebellum. After the 1st course of chemotherapy and whole brain radiation, cognitive function, especially the short-term memory, remarkably improved and the HDS-R score increased to 21/30. However, the tumor again increased in size during the 3(rd) and 4(th) courses of chemotherapy. Interestingly, cognitive function also worsened again and the score of HDS-R declined to 15/30, 20 weeks after the start of chemotherapy. Limbic encephalitis can be associated with malignant tumors, such as small cell lung carcinoma, and some reported cases have shown a cognitive improvement after tumor therapy. In our case, we also observed a reworsening of the cognitive function in association with the acquired chemoresistence.