18F-DPA714 PET in MRI-negative autoimmune encephalitis: a supportive approach to aiding neuroinflammation identification, disease severity correlation, and treatment response prediction.

PURPOSE OF THE REPORT: Conventional magnetic resonance imaging (MRI) has limitations in detecting abnormalities in autoimmune encephalitis (AIE). This retrospective study evaluated the utility of 18F-DPA714 PET, a potential neuroinflammation biomarker, in MRI-negative AIE patients.

MATERIALS AND

METHODS

60 MRI-negative possible AIE patients (mean age 31.68 ± 11.05 years; 60% male) and ten age-matched healthy controls underwent 18F-DPA714 PET. Only high-affinity translocator protein (TSPO) binders were included. Clinical severity scores (mRS, CASE) were collected. Abnormal PET uptake was defined voxel-wise, using a threshold of the mean SUVR + 2SDs derived from the HCs. 34 patients had follow-up PET/MRI post-immunotherapy.

RESULTS

Among the 60 MRI-negative AIE patients, 39 (65%) exhibited abnormally elevated 1⁸F-DPA714 uptake, with the highest positivity rate in the occipital lobes. Uptake patterns corresponded to specific symptoms, such as mesial temporal involvement in cognitive impairment. Quantitatively, baseline PET activity (SUVRmax, SUVRmean) was significantly correlated with baseline clinical severity (mRS, CASE). At follow-up, PET activity remained significantly correlated with mRS and CASE scores, and reductions in PET activity paralleled clinical improvement. Additionally, higher baseline PET activity was associated with greater subsequent brain volume loss.

CONCLUSION

18F-DPA714 PET detected neuroinflammation in a substantial proportion of MRI-negative AIE patients, with quantitative uptake correlating with disease severity. Longitudinal findings suggest that post-treatment decreases in 18F-DPA714 uptake may be associated with reduced subsequent brain volume loss. These results support the potential role of 18F-DPA714 PET/MR as an adjunctive imaging method for disease assessment in MRI-negative AIE.