Autoimmune and infectious encephalitis: development of a discriminative tool for early diagnosis and initiation of therapy.

Background: Encephalitis originates from diverse autoimmune and infectious etiologies. Diagnostic challenges arise due to the spectrum of presentation and the frequent absence of specific biomarkers. This study aimed to comprehensively characterize and differentiate autoimmune encephalitis (AE) from infectious encephalitis (IE) in adults, and disentangle clinical, paraclinical, and therapeutic differences.

Methods: A cohort study spanning 10 years was conducted across three Austrian tertiary care hospitals. Inclusion criteria comprised adults with probable or definite encephalitis. Demographics, clinical features, technical findings, treatment modalities, and outcomes were collected from the electronic patient files. A follow-up was performed via telephone interviews and clinical visits.

Results: Of 149 patients, 17% had AE, 73% IE, and 10% encephalitis of unknown etiology. Significant differences between AE and IE included the prevalence of acute symptomatic seizures (AE: 85% vs. IE: 20%, p < 0.001), fever (8% vs. 72%, p < 0.001), headache (15% vs. 61%, p < 0.001), and focal neurological deficits (56% vs. 23%, p = 0.004), respectively. Paraclinical differences comprised lower CSF pleocytosis in AE compared to IE (median 6 cells/µl vs. 125 cells/µl, p < 0.001). Epileptic discharges on EEG and MRI lesions were more prevalent in AE than IE (50% vs. 14%, p < 0.001; 50% vs. 28%, p = 0.037). The modified Rankin Scale scores at discharge and last follow-up (median duration 2304 days, IQR 1433-3274) indicated favorable outcomes in both groups.

Conclusion: This comprehensive analysis provides insights into the epidemiology, clinical, paraclinical, and therapeutic aspects and the outcomes of AE and IE in adults. We developed a diagnostic tool that facilitates early differentiation between AE and IE, aiding in timely therapeutic decision-making.