FDG ‐ PET Associations With Disease Severity and Outcomes in NMDA ‐Receptor IgG Autoimmune Encephalitis

BACKGROUND: Patients with N-methyl-D-aspartate (NMDA) receptor-immunoglobulin G (IgG) autoimmune encephalitis (NMDAR-IgG AE) demonstrate occipital lobe hypometabolism on baseline brain fluorodeoxyglucose-positron emission tomography (bFDG-PET). The goal of this study was to determine whether there is an association between bFDG-PET findings, disease severity, and clinical outcomes in these patients. METHODS: This retrospective analysis included adult patients with NMDAR-IgG AE who underwent bFDG-PET within 3 months of symptom onset. Qualitative and quantitative assessments of bFDG-PET findings were performed. Spearman's correlation analysis was used to evaluate potential associations between bFDG-PET findings and clinical severity at diagnosis and at 1 year using modified Rankin Scale (mRS) and Clinical Assessment Scale for Autoimmune Encephalitis (CASE) scores. RESULTS: Sixteen patients (13 women, 3 men; median age, 29.0 years) were included in the analysis. The median time between symptom onset and bFDG-PET was 5 weeks (interquartile range: 3-8). All patients received immunosuppressive therapy. Qualitative and quantitative assessments demonstrated the highest correlation between occipital lobe hypometabolism and clinical severity at diagnosis (Quantitative: mRS: -0.65 [95% confidence interval (CI): -0.87, -0.22]; CASE: -0.68 [95% CI: -0.88, -0.28]). At 1 year (n = 12), quantitative baseline occipital lobe hypometabolism was correlated with higher mRS scores (-0.71 [95% CI: -0.91, -0.23]). CONCLUSIONS: In patients with NMDAR-IgG AE, occipital lobe hypometabolism on baseline bFDG-PET is correlated with mRS and CASE scores at the time of diagnosis and mRS scores 1 year later, suggesting that bFDG-PET findings correlate with disease severity and longitudinal outcomes. However, studies with larger patient populations are needed to confirm these findings.