Decrease in the cortex/striatum metabolic ratio on [18F]-FDG PET: a biomarker of autoimmune encephalitis

Abstract

Purpose: The aim of this 18 F-FDG PET study was to determine the diagnostic value of the cortex/striatum metabolic ratio in a large cohort of patients suffering from autoimmune encephalitis (AE) and to search for correlations with the course of the disease. Methods:We retrospectively collected clinical and paraclinical data of patients with AE, including brain 18 F-FDG PET/CT. Whole-brain statistical analysis was performed using SPM8 software after activity parametrization to the striatum in comparison to healthy subjects. The discriminative performance of this metabolic ratio was evaluated in patients with AE using receiver operating characteristic curves against 44 healthy subjects and a control group of 688 patients with MCI. Relationship between cortex/striatum metabolic ratios and clinical/paraclinical data was assessed using univariate and multivariate analysis.Results: Fifty-six patients with AE were included. In comparison to healthy subjects, voxel-based statistical analysis identified one large cluster (p-cluster<0.05, FWE corrected) of widespread decreased cortex/striatum ratio in patients with AE. The mean metabolic ratio was significantly lower for AE patients (1.16 ± 0.13) than for healthy subjects (1.39 ± 0.08; p < 0.001) and than for MCI patients (1.32 ± 0.11; p < 0.001). A ratio threshold of 1.23 allowed to detect AE patients with a sensitivity of 71 %, and a specificity of 82% against MCI patients and 98% against healthy subjects. A lower cortex/striatum metabolic ratio had a trend towards shorter delay before 18 F-FDG PET/CT (p = 0.07) in multivariate analysis. Conclusion:The decrease in the cortex/striatal metabolic ratio has a good early diagnostic performance for the differentiation of AE patients from controls.

International consensus recommendations for management of new onset refractory status epilepticus including febrile infection‐related epilepsy syndrome: Statements and supporting evidence

“…As emerging data have demonstrated specific brain PET patterns in some NORSE etiologies (e.g. autoimmune encephalitis), 62 the indications for PET, in particular in the postacute phase, may increase in the future. Malignancy screening (computed tomography [CT] of chest, pelvis, and abdomen) should be performed in a majority of patients with cryptogenic NORSE/FIRES (M = 9, MA = 9, MP = 7.5, LA = 77.1%, LD = 4.2%).Malignancy screening should be considered in the diagnostic workup in all patients with cryptogenic NORSE but is of particular importance in adults, as the prevalence of paraneoplastic etiologies is substantially lower in children 7 Malignancy screening should include whole body PET when other testing, including CT of chest, pelvis, and abdomen, remains negative (M = 8, MA = 8, MP = 7, LA = 89.2%, LD = 2.7%).In a recent review on NORSE that included 197 publications, whole body PET was performed in 4.6% of patients 7 .…”

“…As emerging data have demonstrated specific brain PET patterns in some NORSE etiologies (e.g. autoimmune encephalitis), 62 the indications for PET, in particular in the postacute phase, may increase in the future. Malignancy screening (computed tomography [CT] of chest, pelvis, and abdomen) should be performed in a majority of patients with cryptogenic NORSE/FIRES (M = 9, MA = 9, MP = 7.5, LA = 77.1%, LD = 4.2%).…”

“…As emerging data have demonstrated specific brain PET patterns in some NORSE etiologies (e.g. autoimmune encephalitis), 62 the indications for PET, in particular in the postacute phase, may increase in the future.…”

Positron emission tomography in autoimmune encephalitis: Clinical implications and future directions

“…The result showed that the ratio of patients with AE was significantly lower than that of patients with mild cognitive impairment and healthy controls. 42 FDG-PET scan has also revealed striatal hypermetabolism assessed qualitatively and semi-quantitatively, with normal uptake in the cortex and cerebellum in a case of VGKCC limbic encephalitis. 43 Putaminal standardized uptake value ratios (SUVRs) normalized to global brain (P), thalamus (P/Th), and midbrain (P/Mi) were also used to evaluate for diagnostic accuracy.…”

“…Another study regarded cortex/striatum ratio in the voxel‐based analysis of FDG‐PET as a biomarker to uncover metabolism changes. The result showed that the ratio of patients with AE was significantly lower than that of patients with mild cognitive impairment and healthy controls 42 . FDG‐PET scan has also revealed striatal hypermetabolism assessed qualitatively and semi‐quantitatively, with normal uptake in the cortex and cerebellum in a case of VGKCC limbic encephalitis 43 .…”