However, among these cases described in Japan, there is a subgroup of severe but often reversible encephalitis that predominantly affects young women, called juvenile acute nonherpetic encephalitis

However, among these cases described in Japan, there is a subgroup of severe but often reversible encephalitis that predominantly affects young women, called juvenile acute nonherpetic encephalitis. acyclovir patient was deteriorated; thus, a paraneoplastic syndrome was suspected. Chest CT showed a right paratracheal lymph node mass, while a biopsy revealed neuroendocrine lung cancer. Auto antibodies to Hu were also detected. The patient was treated with steroids and chemotherapy. Six months later, he had complete tumour remission and marked neurological improvement.Discussion. PLE can rarely invade acutely, being indistinguishable from herpetic encephalitis. Inclusion of PLE in the differential diagnosis of acute SMAP-2 (DT-1154) encephalitis is of great clinical significance. == 1. Introduction == Limbic encephalitis (LE) is a rather rare disorder that mainly affects limbic structures and is characterized by mood-personality changes, sleep disturbances, seizures, hallucinations, and short-term memory loss that can progress to dementia. In most patients with typical LE, the diagnosis is suggested by the clinical presentation, combined with EEG findings (epileptic activity in one or both temporal lobes and focal or generalized slow activity), MRI (hyperintense signals in the medial portion of one or both temporal lobes), and the indicated CSF inflammatory changes. Although nonparaneoplastic and paraneoplastic limbic encephalitis (PLE) have similar clinical features, identification of the paraneoplastic cause commonly depends on finding the tumour, the paraneoplastic antibodies, or both [1]. PLE results from production of a neuronal protein by a tumour, which precipitates an immune-mediated reaction (humoral and T-cell mediated) against both the tumour and the central nervous system itself. There are two types of PLE, one with antibodies to intracellular antigens such as Hu, Ma2, CRMP5, and amphiphysin, that is considered to be T-cell mediated, and LE with antibodies to cell-membrane antigens such as LGI1, CASPR2, NMDA, AMPA, and GABA. These antibodies are more likely directly involved in pathogenesis; thus, these forms of LE are more responsive to immune-based treatment. Although they are usually non-paraneoplastic, there is a variable percentage of an associating tumour [1]. PLE complicates several types of cancer, mainly small-cell lung carcinoma, testicular germ-cell neoplasms, breast cancer, thymoma, Hodgkin’s lymphoma, or teratoma. PLE typically follows a subacute or chronic clinical course, with progression of symptoms within weeks to months [13]. Herein, we report a patient with PLE, initially presenting as acute herpetic encephalitis. == 2. Case Presentation == A 56-year-old male was admitted for evaluation of headache, fever (up to 38C), and acute confusional LEPR state since two days. His past medical history was remarkable for arterial hypertension on perindopril 4 mg od and heavy smoking (40 cig/day). There were no neurologically affected family members. On neurological examination he was alert but confused with a Mini Mental Status Examination (MMSE) score of 15/30 (orientation to time 1/5, orientation to place 1/5, registration 3/3, attention and calculation 1/5, recall 0/3, language and complex commands 8/8, and construction 1/1). There were no meningeal or pyramidal signs, cranial nerves were intact and there was no evidence of sensory dysfunction. Brain CT was normal, while CSF analysis revealed marked pleocytosis (170 cells/mm3; lymphocytes: 90%), increased protein (120 mg/dL) and normal glucose (71 mg/dL, serum: 110 mg/dL). EEG showed diffuse slow activity with paroxysmal slow wave bursts. Brain MRI revealed bilateral enhancing T2 hyperintense lesions in medial temporal lobes (Figures1(a)and1(b)). A working diagnosis of acute herpetic SMAP-2 (DT-1154) encephalitis was rendered and patient was treated with intravenous acyclovir and levetiracetam. Routine laboratory assays were normal. Serological tests and CSF polymerase chain reaction for infectious pathogens (HSV1/2, VZV, CMV, HHV-6, and Treponema pallidum) were negative. On the third day of his hospitalization, the patient developed aphasia, agitation, and irritability, accompanied by two generalized tonic-clonic seizures that were treated with valproic acid. Six days later, he became afebrile but his cognitive function continued to decline, despite treatment with intravenous acyclovir. A new lumbar puncture was performed that revealed normal cell count and protein, with positive oligoclonal bands. A paraneoplastic syndrome was suspected; thus, chest-abdomen CT and full gastrointestinal endoscopy were performed. Chest CT showed a right paratracheal lymph node mass that was confirmed with chest MRI (Figure 2). In addition, serological tests for onconeuronal SMAP-2 (DT-1154) antibodies revealed autoantibodies to Hu. Thoracic surgeon consultation recommended a thoracotomy, where a biopsy demonstrated a large cell neuroendocrine carcinoma..