The boundary between gray and white matter is unclear. 58 years. Of the 23 cases with complete clinical data, their main manifestations were epileptic seizures (65%), mental and behavioral abnormalities (52%), and cognitive impairment (48%). 7 (30.4%) cases had tumors: 5 small cell lung cancer (SCLC), 1 rectum adenocarcinoma (moderately differentiated) and 1 esophageal squamous cell carcinoma. MRI showed 5 (22%) cases had T2 FLAIR increased signals in cortex but with different regions affected. One of the two patients scanned for PET-CT showed hypermetabolism in the left temporal lobe region. The disease course ranged from 5 days to 3 years. 2 patients (one had esophageal AZ1 carcinoma) without immunotherapy and 3 patients (one had SCLC) that did not response to immunotherapy died soon after diagnosis. 18 patients improved after immunotherapy while 3 (all had SCLC) died after relapses. The PDGFRA prevalence of epileptic seizures and malignancies was significantly lower in the survival group than in the deceased group at 18-months follow-up, the same as the admission mRs score. Serum fibrinogen, cerebrospinal fluid immunoglobulin G quotient, and 24-hour intrathecal synthesis rate were significantly lower in the survival groups as well. == Conclusions == Cortex T2 FLAIR abnormalities were only observed in a small proportion of anti-GABABR encephalitis patients with heterogeneous MRI phenotypes. High mRS score at admission, epileptic seizures and the presence of a tumor indicated a poor prognosis, while the underlying mechanism of the later two factors should be investigated further. Keywords:anti-GABABR encephalitis, clinical characteristics, MRI, prognosis, small cell lung cancer == 1. Introduction == Autoimmune encephalitis is usually mediated by autoantibodies against different neuronal surface proteins and ion channels in the brain. Since the discovery of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis (1), many other autoantibodies targeting antigens in the brain have been identified (2,3). Anti-gamma-aminobutyric acid type B receptor (Anti-GABABR) encephalitis was first described by Lancaster et al. in 2010 2010 in patients with predominant limbic symptoms including seizures, mental and behavioral abnormalities, and memory loss, in the presence [mostly small-cell lung cancer (SCLC)] or absence of a tumor (4). GABABR antibodies were also found in patients with ataxia, opsoclonus-myoclonus syndrome (OMS), status epilepticus, or rapidly progressive dementia indicating that diverse clinical phenotypes may be related to this antibody (5,6). The presence of anti-GABABR AZ1 in cerebrospinal fluid (CSF) and/or serum, mostly detected by fixed cell-based assay that make use AZ1 of HEK cells over-expressing GABABR1 and GABABR2 subunits, is the key factor for diagnosis. Other assays can also confirm positive identification of anti-GABABR, such as live cell-based assay, rat brain immunohistochemistry, and/or cultured primary neurons (1,4,7). The sensitivity of the CSF for anti-GABABR identification was reported to be higher than serum, whereas low levels of anti-GABABR antibodies could also be identified in CSF or serum samples from patients with other diseases, which means that the interpretation of low- antibody levels is complex (4,5,7). Notably, a study reported the CSF titers to be higher in 5 out of 6 patients than serum, which indicated a high prevalence of intrathecal synthesis in this studied group (8). Moreover, several reports have suggested the co-existence of other auto-antibodies along with anti-GABABR. These autoantibodies include those against GAD, VGCC, CRMP5, and SOX1 (912). There have been several clinical reports of anti-GABABR encephalitis in recent years; most of them, however, focused on the demographical features of the patients with inconsistent manifestations (47,13,14). In the initial report from Lancaster et al., 2010, 15 cases were reported with anti-GABABR; all presented with seizures and other symptoms related to the limbic system. 7 of them had tumors (5 had SCLC) and other autoantibodies. Hftberger et al. reported another 20 cases in 2013, 17 of which had seizures and 19 of them developed limbic encephalitis (LE). Fifty percent of the cases had SCLC. Notably, 3 of them (6%) showed other symptoms including ataxia, OMS, and status epilepticus. Van Coevorden-Hameete, et al. reported 32 cases with anti-GABABR, 66% of the patients had tumors, mostly SCLC. The most prominent symptoms of this cohort were behavioral abnormalities (97%), and seizures (90%). Strikingly, 4 of the 32 cases (12.5%) had rapidly progressive dementia. Thus, the clinical phenotypes of anti-GABABR encephalitis are rather diverse though predominantly presenting as limbic encephalitis, associated with SCLC. Studies from China reported comparable conclusions as mentioned above,.
