Diagnostic Value of¹⁸F-FDG PET/CT Versus MRI in the Setting of Antibody-Specific Autoimmune Encephalitis

Abstract

Diagnosis of autoimmune encephalitis presents some challenges in the clinical setting because of varied clinical presentations and delay in obtaining antibody panel results. We examined the role of neuroimaging in the setting of autoimmune encephalitides, comparing the utility of 18 F-FDG PET/CT versus conventional brain imaging with MRI. Methods: A retrospective study was performed assessing the positivity rate of MRI versus 18 F-FDG PET/CT during the initial workup of 23 patients proven to have antibody-positive autoimmune encephalitis. 18 F-FDG PET/CT studies were analyzed both qualitatively and semiquantitatively. Areas of cortical lobar hypo (hyper)-metabolism in the cerebrum that were 2 SDx from the mean were recorded as abnormal. Results: On visual inspection, all patients were identified as having an abnormal pattern of 18 F-FDG uptake. In semiquantitative analysis, at least 1 region of interest with metabolic change was identified in 22 of 23 (95.6%) patients using a discriminating z score of 2. Overall, 18 F-FDG PET/ CT was more often abnormal during the diagnostic period than MRI (10/23, 43% of patients). The predominant finding on brain 18 F-FDG PET/CT imaging was lobar hypometabolism, being observed in 21 of 23 (91.3%) patients. Hypometabolism was most commonly observed in the parietal lobe followed by the occipital lobe. An entire subset of antibody-positive patients, anti-N-methyl-D-aspartate receptor (5 patients), had normal MRI results and abnormal 18 F-FDG PET/CT findings whereas the other subsets demonstrated a greater heterogeneity. Conclusion: Brain 18 F-FDG PET/CT may play a significant role in the initial evaluation of patients with clinically suspected antibody-mediated autoimmune encephalitis. Given that it is more often abnormal when compared with MRI in the acute setting, this molecular imaging technique may be better positioned as an early biomarker of disease so that treatment may be initiated earlier, resulting in improved patient outcomes.

Different FDG‐PET metabolic patterns of anti‐AMPAR and anti‐NMDAR encephalitis: Case report and literature review

“…As illustrated in Figures and , genetic expression patterns were similar between AMPAR and NMDAR; the protein densities of AMPAR and NMDAR were both high in the temporal and parietal multimodal association areas, but the densities were more frontal‐dominant for AMPAR and more occipital‐dominant for NMDAR. The high occipital density of NMDAR echoes the occipital hypometabolism in our patient and other case series (Leypoldt et al, ; Probasco et al, ; Solnes et al, ; Yuan et al, ).…”

“…In autoimmune encephalitis, the cortical hypometabolism may or may not be combined with hypermetabolic foci (Fisher, Patel, Lai, & Schulz, ). Z ‐score and 3D‐SSP visualization help clinical physicians explain patients' cognitive dysfunction in correlation with regions of glucose hypometabolism and are applicable to clinical use (Solnes et al, ). The receptor maps of gene expression and protein density helped us understand the topographical distribution and correlations with FDG‐PET hypometabolism regions.…”

FDG-PET and MRI in the Evolution of New-Onset Refractory Status Epilepticus

“…Others have reported increased sensitivity of FDG-PET versus MR imaging during the initial evaluation. 29,33,34 Our findings mirrored this: Fifty percent of MR imaging scans initially had abnormal findings compared with 100% of FDG-PET scans. With time, an increasing proportion of MRIs showed some abnormal findings.…”

Clinical approach to the diagnosis of autoimmune encephalitis in the pediatric patient

“…1 Small retrospective adult AE studies have proposed that functional PET and SPECT studies may demonstrate brain dysfunction, but experience is limited in pediatric AE. 35,36 A normal EEG is unusual in children with AE during active disease, although prolonged EEG may be needed for improved sensitivity. Therefore, focal or generalized seizures, epileptiform discharges, and encephalopathic changes, such as diffuse or focal slowing, may help to distinguish AE from primary psychiatric disorders or PANS.…”