Hypometabolism of the left middle/medial frontal lobe on FDG‐PET in anti–NMDA receptor encephalitis: Comparison with MRI and EEG findings

OBJECTIVES: To investigate changes in brain‐glucose metabolism in anti‐N‐methyl‐D‐aspartate receptor (NMDAR) encephalitis, and compare results with MRI and electroencephalography (EEG) findings at different disease stages. METHODS: The clinical data of 18 patients (median age, 35 years; 11 men) were retrospectively collected. Patients were divided into groups based on the time of symptom onset to examination, (≤1 month, >1 but ≤3 months, >3 months). Two‐sample t‐test results were compared with age and sex‐paired healthy controls using statistical parametric mapping and verified using a NeuroQ software normal database with a discriminating z‐score of 2. RESULTS: Abnormal patterns on FDG‐PET differed over time (T = 3.21–8.74, Z = 2.68–4.23, p < 0.005). Regional analysis showed hypometabolic left middle or medial frontal cortex in 4/5, 5/7, and 5/6 patients, respectively. Time‐subgroup analysis revealed hypermetabolic supertemporal cortex in 4/5, 5/7, and 2/6, patients, respectively. MRI and EEG abnormalities in any region and stage occurred in 10/18 and 10/16 patients, respectively. MRI and EEG time‐subgroup analysis showed abnormalities in 5/9, 4/5, and 1/4, and 1/3, 6/7, and 3/6 patients, respectively. Abnormal temporal lobes were detected most frequently in MRI analyses and occurred in 3/10 patients. CONCLUSIONS: Decreased left middle/medial frontal metabolism could be common to all stages. Metabolism in other regions, MRI, and EEG results were associated with the progression of anti‐NMDAR encephalitis. The sensitivity rate of FDG‐PET was superior to that of MRI and EEG.