Long-term survival (≥2 years) in subacute sclerosing panencephalitis: a systematic review of prolonged survivors

Purpose: Subacute sclerosing panencephalitis (SSPE) is a progressive and often fatal disorder with highly variable survival. This systematic review aimed to characterize long-term survival (≥2 years), remission, and stabilization, and identify determinants of favorable outcomes. Methods: A systematic review was conducted according to PRISMA 2020 guidelines. Studies including confirmed SSPE cases were considered eligible for inclusion. Individual patient analysis was restricted to cases with ≥2 years of follow-up. Data were extracted at the patient and cohort levels. Results: Analysis of 77 patients demonstrated that survival beyond 2 years is achievable but variable. Survival distribution showed 44.2% surviving 2 to <5 years, 28.6% surviving 5 to <10 years, and 27.3% surviving ≥10 years. Although 62.3% initially achieved remission or stabilization, 31.2% later developed progression, severe disability, or death. Reported factors associated with prolonged survival included treatment responsiveness (62.3%), slow disease progression (24.7%), and relapsing-remitting or biphasic patterns (20.8%). Additional contributors were host-related factors (18.2%), adult-onset disease (10.4%), early diagnosis, and electroencephalographic improvement. Across 31 cohort studies, overall survival remained poor. Survival beyond 2 years was inconsistently reported and varied widely. Remission or stabilization was observed in some studies, but disease progression remained the predominant outcome. Mortality ranged from low to very high across cohorts. Reported factors associated with improved survival included slower disease progression, older age at onset, earlier stage at diagnosis, and use of therapies such as inosine pranobex and interferon. Conclusion: SSPE survival outcomes show marked heterogeneity. Although prolonged survival occurs in some, most patients have poor outcomes, emphasizing the importance of early diagnosis and the need for effective therapies.