ImportanceRapid and accurate diagnosis of autoimmune encephalitis encourages prompt initiation of immunotherapy toward improved patient outcomes. However, clinical features alone may not sufficiently narrow the differential diagnosis, and awaiting autoantibody results can delay immunotherapy.ObjectiveTo identify simple magnetic resonance imaging (MRI) characteristics that accurately distinguish 2 common forms of autoimmune encephalitis, LGI1- and CASPR2-antibody encephalitis (LGI1/CASPR2-Ab-E), from 2 major differential diagnoses, viral encephalitis (VE) and Creutzfeldt-Jakob disease (CJD).Design, Setting, and ParticipantsThis cross-sectional study involved a retrospective, blinded analysis of the first available brain MRIs (taken 2000-2022) from 192 patients at Oxford University Hospitals in the UK and Mayo Clinic in the US. These patients had LGI1/CASPR2-Ab-E, VE, or CJD as evaluated by 2 neuroradiologists (discovery cohort; n = 87); findings were validated in an independent cohort by 3 neurologists (n = 105). Groups were statistically compared with contingency tables. Data were analyzed in 2023.Main Outcomes and MeasuresMRI findings including T2 or fluid-attenuated inversion recovery (FLAIR) hyperintensities, swelling or volume loss, presence of gadolinium contrast enhancement, and diffusion-weighted imaging changes. Correlations with clinical features.ResultsAmong 192 participants with MRIs reviewed, 71 were female (37%) and 121 were male (63%); the median age was 66 years (range, 19-92 years). By comparison with VE and CJD, in LGI1/CASPR2-Ab-E, T2 and/or FLAIR hyperintensities were less likely to extend outside the temporal lobe (3/42 patients [7%] vs 17/18 patients [94%] with VE; P < .001, and 3/4 patients [75%] with CJD; P = .005), less frequently exhibited swelling (12/55 [22%] with LGI1/CASPR2-Ab-E vs 13/22 [59%] with VE; P = .003), and showed no diffusion restriction (0 patients vs 16/22 [73%] with VE and 8/10 [80%] with CJD; both P < .001) and rare contrast enhancement (1/20 [5%] vs 7/17 [41%] with VE; P = .01). These findings were validated in an independent cohort and generated an area under the curve of 0.97, sensitivity of 90%, and specificity of 95% among cases with T2/FLAIR hyperintensity in the hippocampus and/or amygdala.Conclusions and RelevanceIn this study, T2 and/or FLAIR hyperintensities confined to the temporal lobes, without diffusion restriction or contrast enhancement, robustly distinguished LGI1/CASPR2-Ab-E from key differential diagnoses. These observations should assist clinical decision-making toward expediting immunotherapy. Their generalizability to other forms of autoimmune encephalitis and VE should be examined in future studies.

中文翻译：

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LGI1抗体和CASPR2抗体脑炎的磁共振成像特征

重要性快速准确地诊断自身免疫性脑炎有助于立即启动免疫治疗，以改善患者的预后。然而，仅凭临床特征可能不足以缩小鉴别诊断范围，等待自身抗体结果可能会延迟免疫治疗。 目的 确定简单的磁共振成像 (MRI) 特征，以准确区分 2 种常见形式的自身免疫性脑炎：LGI1 和 CASPR2 抗体脑炎 (LGI1) /CASPR2-Ab-E），来自 2 个主要鉴别诊断，病毒性脑炎 (VE) 和克雅氏病 (CJD)。设计、设置和参与者这项横断面研究涉及对第一个可用的脑 MRI 的回顾性、盲法分析（2000 年至 2022 年拍摄）来自英国牛津大学医院和美国梅奥诊所的 192 名患者。经 2 名神经放射科医生评估，这些患者患有 LGI1/CASPR2-Ab-E、VE 或 CJD（发现队列；n = 87）；研究结果在独立队列中由 3 名神经科医生 (n = 105) 进行了验证。各组与列联表进行统计比较。数据于 2023 年进行分析。 主要结果和测量 MRI 结果包括 T2 或液体衰减反转恢复 (FLAIR) 高信号、肿胀或体积损失、钆对比增强的存在以及扩散加权成像变化。与临床特征的相关性。结果在 192 名接受 MRI 检查的参与者中，71 名女性（37%）和 121 名男性（63%）；中位年龄为 66 岁（范围为 19-92 岁）。与 VE 和 CJD 相比，在 LGI1/CASPR2-Ab-E 中，T2 和/或 FLAIR 高信号不太可能延伸到颞叶外（3/42 例患者 [7%] vs 17/18 例患者 [94%]） VE；磷< .001，以及 3/4 [75%] 患有克雅氏病的患者；磷= .005），较少出现肿胀（LGI1/CASPR2-Ab-E 组为 12/55 [22%]，VE 组为 13/22 [59%]；磷= .003），并且没有显示扩散限制（0 名患者 vs VE 患者 16/22 [73%]，CJD 患者 8/10 [80%]；两者磷< .001）和罕见的对比度增强（VE 时为 1/20 [5%] vs 7/17 [41%]；磷= .01)。这些结果在一个独立队列中得到了验证，在海马和/或杏仁核 T2/FLAIR 高信号病例中，曲线下面积为 0.97，敏感性为 90%，特异性为 95%。结论和相关性在本研究中，T2和/或局限于颞叶的 FLAIR 高信号，没有扩散限制或对比度增强，可以将 LGI1/CASPR2-Ab-E 与关键鉴别诊断有力地区分开来。这些观察结果应有助于加快免疫治疗的临床决策。在未来的研究中应检查它们对其他形式的自身免疫性脑炎和 VE 的普遍性。