Abstract: Objective  To study the imaging features of ¹⁸F-deoxyglucose (FDG) positron emission tomography（PET）/computed tomography（CT） in the head of patients with anti-leucine-rich glioma-inactivated 1 （LGI1） antibody autoimmune encephalitis (AE), and to evaluate the value of PET/CT in the early diagnosis of anti-LGI1 antibody AE. Methods  The data of 43 patients with LGI1-AE diagnosed in the Department of Neurology, Beijing Tiantan Hospital,  Capital Medical University from October 2014 to November 2020 were retrospectively analyzed, including 24 patients in acute phase (56%), 19 patients in chronic phase (44%), and AE patients whose anti-LGI1 autoimmune antibodies were positive in cerebrospinal fluid or/and serum. The imaging and clinical features of ¹⁸F-FDG PET/CT were analyzed. Results  ¹⁸F-FDG PET imaging showed that 40 LGI1-AE patients (93%) had obvious metabolic abnormalities, while only 26 patients (60%) had abnormal magnetic resonance imaging (MRI) signals (P < 0.05). The abnormal metabolism of ¹⁸F-FDG PET is reversible after treatment, and the metabolism of 18F-FDG PET in most patients is almost normal after discharge. The hypermetabolic regions of patients with LGI1-AE are located in the basal ganglia (BG) and medial temporal lobe (MTL). Hypermetabolism in the BG was observed in 33 patients (77%), and hypermetabolism in the MTL was observed in 72% of the patients. A total of 22 patients (51%) showed facial arm dystonia seizures (FBDS), whereas rest showed non-FBDS symptoms (49%). Hypermetabolism in the BG was detected only in 7 patients with FBDS (7/21), while that  detected in only 2 patients without FBDS (2/19) (33% vs 10%). Conclusion  ¹⁸F-FDG PET imaging was more sensitive in the early diagnosis of LGI1-AE. Most of the patients with FBDS showed hypermetabolism isolated in the BG, suggesting  the potential involvement of the BG.

Key words: anti-leucine-rich glioma-inactivated 1（ LGI1）antibody,  , encephalitis, autoimmune disease, 18F-deoxyglucose（18F-FDG）, positron emission tomography（PET）