To compare PET brain scan results of patients with and without AIE to determine specificity and sensitivity of various scan findings.

Diagnosis of autoimmune encephalitis (AIE) relies on meeting specific criteria. This includes abnormalities identified on MRI, EEG and CSF analysis. Unfortunately, many of these paraclinical tests lack specificity and sensitivity. More recently, there is interest in positron emission tomography (PET) brain scans to aid in diagnosis; however, their utility is debated, and there is no consensus regarding which findings are most suggestive of AIE.

Patients with PET brain scans completed in Edmonton for the question of AIE between 2013 and 2023 were obtained through database search. PET activity in various brain regions were quantified using specialized software. Patients meeting clinical AIE criteria were identified via retrospective chart review. Specificity and sensitivity of PET scan findings were calculated. T-test for independent samples was used to determine correlations between PET scan findings and clinical syndromes.

A total of 118 patient scans were reviewed. This included 31 patients meeting criteria for possible (11), probable (5), or definite AIE (15). AIE subtypes included NMDA (6), limbic (6), seronegative (3), paraneoplastic (4), and unknown/other (12). Neither temporal lobe nor cerebellum metabolism was significantly different between those with or without AIE (p>0.05). Specificity of temporal lobe hypermetabolism, hypometabolism, and cerebellum hypermetabolism for AIE was 84%, 71%, and 76% respectively. Sensitivity was 29%, 16%, and 26% respectively.

PET scan findings, including temporal lobe and cerebellum metabolism, have specificity ranging from 71% - 84% and sensitivity ranging from 16% - 26%, which isn’t dissimilar from other paraclinical tests used in the diagnosis of AIE. Further information regarding clinical factors that impact sensitivity and specificity are needed to assist in determining the utility of PET brain scans in the diagnosis of AIE.