由于病因不同,度过病情危重阶段而幸存的患者的情况也都各不相同。预后往往较差。死亡率和发病率取决于发病的病因、宿主的免疫状态、病变的解剖位置和受累程度、并发症的进展情况、以及开始治疗的时间。在美国,死亡率为 6%至 9%,[4]Vora NM, Holman RC, Mehal JM, et al. Burden of encephalitis-associated hospitalizations in the United States, 1998-2010. Neurology. 2014;82:443-451.http://www.ncbi.nlm.nih.gov/pubmed/24384647?tool=bestpractice.com[6]George BP, Schneider EB, Venkatesan A. Encephalitis hospitalization rates and inpatient mortality in the United States, 2000-2010. PloS One. 2014;9:e104169.http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0104169http://www.ncbi.nlm.nih.gov/pubmed/25192177?tool=bestpractice.com[72]Singh TD, Fugate JE, Rabinstein AA. The spectrum of acute encephalitis: causes, management, and predictors of outcome. Neurology. 2015;84:359-366.http://www.ncbi.nlm.nih.gov/pubmed/25540320?tool=bestpractice.com英国为 12%。[73]Granerod J, Tam CC, Crowcroft NS, et al. Challenge of the unknown: a systematic review of acute encephalitis in non-outbreak situations. Neurology. 2010;75:924-932.http://www.ncbi.nlm.nih.gov/pubmed/20820004?tool=bestpractice.com年龄> 65 岁、免疫功能受损(HIV 或服用免疫抑制药物)、使用机械通气、有昏迷、急性血小板减少症、脑脊液中性粒细胞计数升高、脑水肿和癫痫持续状态的患者的治疗效果不佳。[72]Singh TD, Fugate JE, Rabinstein AA. The spectrum of acute encephalitis: causes, management, and predictors of outcome. Neurology. 2015;84:359-366.http://www.ncbi.nlm.nih.gov/pubmed/25540320?tool=bestpractice.com[74]Thakur KT, Motta M, Asemota AO, et al. Predictors of outcome in acute encephalitis. Neurology. 2013;81:793-800.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3908458/http://www.ncbi.nlm.nih.gov/pubmed/23892708?tool=bestpractice.com
是否会出现远期后遗症取决于年龄、脑炎病因、临床症状的严重程度。[41]Chaudhuri A, Kennedy PG. Diagnosis and treatment of viral encephalitis. Postgrad Med J. 2002;78:575-583.http://pmj.bmj.com/content/78/924/575.longhttp://www.ncbi.nlm.nih.gov/pubmed/12415078?tool=bestpractice.com超过半数的幸存者会出现重度残疾。儿童患者中,长期发病率高达三分之二。包括疲劳、认知障碍、注意力缺陷障碍、语言障碍、运动障碍、共济失调、癫痫发作和人格改变。[75]Michaeli O, Kassis I, Shachor-Meyouhas Y, et al. Long-term motor and cognitive outcome of acute encephalitis. Pediatrics. 2014;133:e546-e552.http://pediatrics.aappublications.org/content/133/3/e546.longhttp://www.ncbi.nlm.nih.gov/pubmed/24534397?tool=bestpractice.com[76]McJunkin JE, Khan R, de los Reyes EC, et al. Treatment of severe La Crosse encephalitis with intravenous ribavirin following diagnosis by brain biopsy. Pediatrics. 1997;99:261-267.http://www.ncbi.nlm.nih.gov/pubmed/9024460?tool=bestpractice.com[77]Fowler A, Stödberg T, Eriksson M, et al. Childhood encephalitis in Sweden: etiology, clinical presentation and outcome. Eur J Paediatr Neurol. 2008;12:484-490.http://www.ncbi.nlm.nih.gov/pubmed/18313340?tool=bestpractice.com[78]Elbers JM, Bitnun A, Richardson SE, et al. A 12-year prospective study of childhood herpes simplex encephalitis: is there a broader spectrum of disease? Pediatrics. 2007;119:e399-e407.http://www.ncbi.nlm.nih.gov/pubmed/17272602?tool=bestpractice.com疾病仅累及小脑的儿童或患有呼吸道合胞病毒性脑炎的儿童往往预后较好。
脑炎后 5 年内癫痫的发病率为 10%,20 年内为 20%。[79]Annegers JF, Hauser WA, Beghi E, et al. The risk of unprovoked seizures after encephalitis and meningitis. Neurology. 1988;38:1407-1410.http://www.ncbi.nlm.nih.gov/pubmed/3412588?tool=bestpractice.com住院期间癫痫发作和脑 MRI 异常是脑炎后癫痫的最强预测因子。脑炎的病因、局灶性神经功能缺损和发作期间脑电图异常不会影响脑炎后癫痫的发展。[80]Singh TD, Fugate JE, Hocker SE, et al. Postencephalitic epilepsy: clinical characteristics and predictors. Epilepsia. 2015;56:133-138.http://onlinelibrary.wiley.com/doi/10.1111/epi.12879/fullhttp://www.ncbi.nlm.nih.gov/pubmed/25523929?tool=bestpractice.com
对于单纯疱疹病毒性脑炎而言,年龄大、意识水平下降和阿昔洛韦治疗延迟或缺失都与高死亡率有关。弥漫性脑水肿和顽固性癫痫发作是其他的不良预后指标。即使如此,幸存者常伴神经功能丧失性后遗症,如(短期)记忆障碍、性格和行为改变、精神问题和嗅觉丧失。[81]McGrath N, Anderson NE, Croxson MC, et al. Herpes simplex encephalitis treated with acyclovir: diagnosis and long term outcome. J Neurol Neurosurg Psychiatry. 1997;63:321-326.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2169720/pdf/v063p00321.pdfhttp://www.ncbi.nlm.nih.gov/pubmed/9328248?tool=bestpractice.com严重的行为和性格改变包括克鲁尔-布西症候群,多见于阿昔洛韦广泛使用前,现在已不再常见。