[A case of paraneoplastic limbic encephalitis associated with neck neuroendocrine carcinoma]

A 69-year-old man presented with a history of personality change for several years. He was admitted to our hospital due to partial seizure. A cerebrospinal fluid test and an electroencephalogram showed no specific abnormalities, but brain magnetic resonance imaging revealed abnormal findings in the right temporal pole, bilateral amygdala to hippocampus, and insular cortex. He was diagnosed with limbic encephalitis accompanied by partial seizure, and received infusion of an antiepileptic agent and acyclovir. Additional examinations for malignancy and autoimmune disease were performed, and neck CT and MRI revealed a neck tumor. Neck lymph node biopsy suggested lymph node metastasis of a neuroendocrine neoplasm derived from other organs. He did not want aggressive treatment involving surgical resection and chemotherapy, and thus, conservative treatment was chosen by an otorhinolaryngologist and immunotherapy was not used. After discharge, the neck tumor grew gradually. To manage the focal mass effect, chemotherapy and surgical resection followed by chemoradiotherapy were performed by the otorhinolaryngologist on days 244 and 325 of the disease course, respectively. Histology of resected tissues disclosed neck neuroendocrine carcinoma derived from a submandibular gland. His personality change improved temporarily after surgical resection, but then worsened again with regrowth of the tumor. He died on day 723. After death, a blood test revealed the presence of anti-amphiphysin antibody. This case suggests that neck neuroendocrine carcinoma can induce paraneoplastic limbic encephalitis, and in such cases, early surgical resection of the neck tumor with suspected lymph node metastasis is necessary both to control symptoms associated with encephalitis and to exclude carcinoma derived from the neck itself.