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.