¹⁸F-FDG PET/CT metabolic patterns and clinical parameters correlate with disease severity in autoimmune encephalitis

To investigate the correlation of ¹⁸F-FDG PET/CT metabolic patterns and clinical parameters with disease severity in patients with autoimmune encephalitis (AE).

We retrospectively analyzed 35 AE patients who underwent ¹⁸F-FDG PET/CT at the Second Affiliated Hospital of Soochow University between March 2021 and December 2023. Clinical and auxiliary examination data were collected and analyzed using the t-test, Mann-Whitney U test, Fisher's exact test, and Spearman correlation. Metabolic patterns on PET/CT were assessed both visually and using Cortex ID software across severity groups.

Among the 35 AE patients (21 males, 14 females), 16 were classified as mild and 19 as moderate-to-severe. Compared to the mild group, the moderate-to-severe group exhibited significantly elevated neutrophil percentages and neutrophil-to-lymphocyte ratio (NLR), alongside reduced lymphocyte percentages, lymphocyte counts, and serum calcium ion levels (Z = -2.75 to 2.30; all p < 0.05). ¹⁸F-FDG PET/CT demonstrated a higher abnormality detection rate than brain MRI (p < 0.05). The most common imaging finding was hypometabolism in the brain parenchyma, predominantly involving the parietal and occipital lobes. Furthermore, CASE scores demonstrated a negative correlation with Z-scores in the right medial frontal lobe, right superior parietal lobe, and bilateral lateral occipital lobes (r = -0.456 to -0.567; all p < 0.05).

In addition to clinical symptoms, specific cerebrospinal fluid and serum biomarkers may help evaluate AE severity. ¹⁸F-FDG PET/CT demonstrates a higher abnormality detection rate than brain MRI, and we preliminarily observed a correlation between regional hypometabolism and clinical severity scores.