[18F]fluorodeprenyl-D2 PET can detect and monitor astrogliosis in anti-LGI1-IgG autoimmune encephalitis

To explore whether detecting local astrogliosis using [18F]fluorodeprenyl-D2 ([18F]F-DED) positron-emission-tomography (PET) uncovers and monitors inflammatory lesions in patients with anti-leucine-rich glioma-inactivated 1 antibody (LGI1-ab) associated autoimmune encephalitis (AE). Dynamic [18F]F-DED PET scans (0–60 min post-injection) were obtained from a cohort of 15 LGI1-AE patients, 9 of whom were re-examined during the disease course, and from 15 controls. PET quantification was performed by kinetic modelling with an image derived input function and calculation of simplified standardized uptake values (SUV). [18F]F-DED SUVr (referenced to the straight gyrus) were analyzed for LGl1-AE target regions, compared between baseline and follow-up PET scans, used to investigate asymmetry of the mesial temporal lobe (MTL), and correlated to routine clinical data. Simplified [18F]F-DED PET quantification of the 30–60 min time-frame showed excellent agreement with kinetic modelling of the full dynamic imaging protocol. In LGI1-AE patients, [18F]F-DED SUVr values were significantly increased by 16% in the MTL (p = .002) and by 12% in the cerebellum (p = .014). [18F]F-DED signals in the MTL significantly declined during the course of the disease (mean follow-up time: 15 months, p = .006). MTL asymmetry (> 5%) of [18F]F-DED SUVr was present in 8/15 of LGI1-AE patients compared to 1/15 controls (p < .001) and showed marked decline between baseline and follow-up in LGI1-AE patients. This pilot study shows that [18F]F-DED PET is a promising tool to monitor regional astrogliosis in LGI1-AE patients and may provide a direct read-out of this important aspect of inflammatory disease activity.